SciForums.com > Science > Physics & Math > The Relativity of Simultaneity PDA View Full Version : The Relativity of Simultaneity Post ReplyCreate New ThreadPages : [1] 2 3 4 5 6 7 Motor Daddy05-12-10, 08:14 AMhttp://www.bartleby.com/173/9.html Einstein says: "Just when the flashes 1 of lightning occur, this point M' naturally coincides with the point M, but it moves towards the right in the diagram with the velocity v of the train." "Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightning flash B took place earlier than the lightning flash A." I contend there is no relativity of simultaneity, that the strikes occurred simultaneously, and that the observer on the embankment and the observer on the train will agree on when the strikes occurred. There is however a distinction between the simultaneity of the strikes, and when the light from the strikes impacts the observers. I realize the light will hit the train observer at different times, as the train is in motion. Therefore, the observer on the train will be hit by the light from the front of the train before the light from the back of the train reaches him. That is a result of the light from the rear of the train having to travel a greater distance until it impacts the train observer. The light from points A and B hits the embankment observer simultaneously, as the strikes occurred at both points when the train and embankment points coincided, and he was at the midpoint. The light from each strike traveled the same speed and the same distance to reach the observer. The conclusion from that is that the embankment observer could not have had a velocity, he was at a true zero velocity. The perceived "relativity of simultaneity" in this example is due to the train observer's failure to acknowledge his own velocity, as is clearly shown with the directional arrow in the example. That incorrect assumption leads him to his false claim that the strikes must have occurred at different times. edit: The board will not allow me to post the URL to Einstein's example. The example can be found in chapter 9 of Einstein's- Relativity The Special and General Theory. Pete05-12-10, 08:30 AMHi Motor Daddy, The whole point of relativity is that the laws of physics still work if we consider the train to be stationary and the ground to be moving past. Bouncing a ball on the moving train feels exactly the same as bouncing a ball on the ground. Galileo figured this out 400 years ago, and why he got in trouble with the Church - he said that the Earth could be spinning, and moving around the Sun, and you wouldn't feel it. The Pope didn't like that idea, and made him shut up about it. Now, for Einstein's relativity things get trickier. We add in the surprising truth that a particular speed of light is one of the laws of physics that are the same regardless of what you consider to be stationary. This very surprising fact has been carefully tested and found to be true. So. If the person on the embankment measures the speed of the light from the lightning flashes as they goes past, they will measure 300,000km/s. And if the person on the train measures the speed of the same flashes of light, they will also measure 300,000km/s. So, the person on the train measures the flashes to have come from the same distance at the same speed, and concludes that they must have taken the same time in transit. So, since they arrived at different times, they must also have been emitted at different times. Try this video: http://www.youtube.com/watch?v=KYWM2oZgi4E Motor Daddy05-12-10, 08:45 AMHi Motor Daddy, The whole point of relativity is that the laws of physics still work if we consider the train to be stationary and the ground to be moving past. Bouncing a ball on the moving train feels exactly the same as bouncing a ball on the ground. The embankment could not have had a velocity, as the strikes occurred when the train's and the embankment's points coincided, and the embankment observer was at the midpoint, and the light reached him at exactly the same time. If the embankment would have been in motion, and the train considered stationary, the lights would have struck the embankment observer at different times, but they didn't. Now, for Einstein's relativity things get trickier. We add in the surprising truth that a particular speed of light is one of the laws of physics that are the same regardless of what you consider to be stationary. This very surprising fact has been carefully tested and found to be true. Light travels independently of all frames, which is why the velocity of the light source is irrelevant. But, the velocity of the "receiver" of the light is VERY important, as a light traveling towards an object with a zero velocity has to travel a shorter distance than if the light were traveling towards an object with a velocity moving away from the light. The light has to travel a greater distance to reach the object. So. If the person on the embankment measures the speed of the light from the lightning flashes as they goes past, they will measure 300,000km/s. And if the person on the train measures the speed of the same flashes of light, they will also measure 300,000km/s. That is because the speed of light is independent of frames. So, the person on the train measures the flashes to have come from the same distance at the same speed, and concludes that they must have taken the same time in transit. So, since they arrived at different times, they must also have been emitted at different times. But again, the person on the train fails to realize that the light traveled a greater distance to reach his midpoint, as he was "hastening to the right." The observer thinks that the light traveled the same distance to reach him, which is false. Pete05-12-10, 08:52 AMThe embankment could not have had a velocity, as the strikes occurred when the train's and the embankment's points coincided, and the embankment observer was at the midpoint, and the light reached him at exactly the same time. If the embankment would have been in motion, and the train considered stationary, the lights would have struck the embankment observer at different times, but they didn't. The strikes only occur when the train's and the embankment's points coincided if we consider the embankment stationary. If we consider the train to be stationary (and Galileo says we can), then we find that the front strike occurred before the train and embankment coincided, and the rear strike occurred afterward. So, we can consider the train to be stationary, and still have the light flashes still meet the embankment observer at the same time. So yes, the embankment could indeed have had a velocity. That is because the speed of light is independent of frames. Don't you see that if the strikes are simultaneous in the train frame, then the train observer must measure a higher speed for the light coming from the front? According to the train observer, both flashes go the same distance - half the length of the train. If the front flash travels that distance in a shorter time, then it must have been going faster. You know, that book by Einstein really isn't the best way to learn this stuff. It's a hundred years old, the language is archaic, and there have been a thousand better explanations written since then. It's not surprising that people find it hard to follow. Motor Daddy05-12-10, 09:03 AMWrong again, MD. Remember, the strikes only occurred when the train's and the embankment's points coincided if we consider the embankment stationary. If we consider the train to be stationary (and Galileo says we can), then we find that the front strike occurred before the train and embankment coincided, and the rear strike occurred afterward. According to the train observer, the light flashes still meet the embankment observer at the same time. So yes, the embankment could indeed have had a velocity. The strikes occurred as the points lined up, at that instantaneous point in time. Choosing to say that it was the embankment with a velocity and the train that was stationary doesn't change the fact the points were aligned when the strikes occurred. You could synchronize 4 clocks, place them on the two points at the train and two point on the embankment. When the clocks are struck they stop, to show what time it was when they were struck. ALL the clocks will read the same, as they were all struck simultaneously. Agreed, the observer on the train will (falsely) conclude that the strikes must have occurred at different times, as the light struck him at different times, but that is when the light strikes him, not when the lightening strikes occurred, which the clocks show simultaneously. Motor Daddy05-12-10, 09:06 AMDon't you see that if the strikes are simultaneous in the train frame, then the train observer must measure a higher speed for the light coming from the front? According to the train observer, both flashes go the same distance - half the length of the train. If the front flash travels that distance in a shorter time, then it must have been going faster. You know, that book by Einstein really isn't the best way to learn this stuff. It's a hundred years old, the language is archaic, and there have been a thousand better explanations written since then. It's not surprising that people find it hard to follow. The observer on the train needs to know how far the light traveled, and how much time it took to travel that distance. The observer on the train must understand that the light from the rear had to travel a greater distance to reach him than the light from the front did. The speed of light is the same for both, but the distance and time travel of the two lights were different. Pete05-12-10, 09:08 AMThe strikes occurred as the points lined up, at that instantaneous point in time. Choosing to say that it was the embankment with a velocity and the train that was stationary doesn't change the fact the points were aligned when the strikes occurred. It seems that you're assuming that simultaneity can't be relative before we begin. Why? I thought that's what you were trying to prove? How can you prove that the strikes were simultaneous by assuming that the strikes were simultaneous? You could synchronize 4 clocks, place them on the two points at the train and two point on the embankment. Can't be done if simultaneity is relative. You're simply assuming that simultaneity is absolute. Motor Daddy05-12-10, 09:13 AMIt seems that you're assuming that simultaneity can't be relative before we begin. Why? I thought that's what you were trying to prove? I'm showing there is no "relativity of simultaneity." How can you prove that the strikes were simultaneous by assuming that the strikes were simultaneous? The example clearly says the points were lined up when the strikeS occurred. There was only one point in time when that could have happened, not two points in time. Can't be done if simultaneity is relative. You're simply assuming that simultaneity is absolute. Not assuming, showing why it is absolute. Pete05-12-10, 09:14 AMThe observer on the train needs to know how far the light traveled, and how much time it took to travel that distance. The observer on the train must understand that the light from the rear had to travel a greater distance to reach him than the light from the front did. The speed of light is the same for both, but the distance and time travel of the two lights were different. Not so. In the train's reference frame, the light flashes both travel the same distance. They both start at one end of the train, and meet in the middle. You said before that "the speed of light is independent of frames". Well, this is what a "frame" is. Using the train reference frame means using rulers at rest on the train to define distance, and clocks at rest on the train to define time. For example: Place a ruler at rest on the train so that lightning strikes at one end of the ruler, and the observer is at the other end of the ruler. The length of the ruler is the distance travelled by the light flash in that reference frame. Pete05-12-10, 09:17 AMI'm showing there is no "relativity of simultaneity." The example clearly says the points were lined up when the strikeS occurred. There was only one point in time when that could have happened, not two points in time. Not assuming, showing why it is absolute. You said: The strikes occurred as the points lined up, at that instantaneous point in time. Choosing to say that it was the embankment with a velocity and the train that was stationary doesn't change the fact the points were aligned when the strikes occurred. i.e. You're simple declaring that the strikes occurred at the same time, in all reference frames. Declaring something to be true is not the same as showing it or proving it. Are you also known as _Jack? Motor Daddy05-12-10, 09:25 AMNot so. In the train's reference frame, the light flashes both travel the same distance. They both start at one end of the train, and meet in the middle. The strikes occurred when the points were lined up. The points lined up once, not twice. Both strikes occurred at that time, which means simultaneously. The light impacted the train observer at different times from the front and rear. Light always travels at the same speed, independently of the frame. If the train observer were to have had a true zero velocity to consider himself "stationary", the lights would have impacted him at the same times, but they didn't. That means the observer had a velocity, which is clearly noted in the diagram with the arrow, and Einstein's own words. You said before that "the speed of light is independent of frames". Well, this is what a "frame" is. It is using rulers at rest on the train to define distance. Place a ruler at rest on the train so that lightning strikes at one end of the ruler, and the observer is at the other end of the ruler. The length of the ruler is the distance traveled by the light flash in that reference frame. It is independent of frames, ie, the distance light travels is independent of the distance between the points of a single frame. Just because the observer sits midpoint of a frame doesn't mean light traveled the same distance to reach him. If the frame has a velocity the light has to travel a DIFFERENT distance, not the distance the observer in that frame measures. Motor Daddy05-12-10, 09:26 AMAre you also known as _Jack? No. Pete05-12-10, 09:31 AMBored already. Sorry MD, perhaps we'll talk again one day. In the meantime, think about why declaring a statement doesn't help you to prove it. And if you want to talk about reference frames, you should first learn what that means. Have fun! Motor Daddy05-12-10, 09:34 AMBored already. Sorry MD, perhaps we'll talk again one day. In the meantime, think about why declaring a statement doesn't help you to prove it. And if you want to talk about reference frames, you should first learn what that means. Have fun! How could you be bored? This is exciting stuff. Do you agree the light from each strike traveled different distances to reach him than what the train observer measured at his midpoint of his own frame? AlphaNumeric05-12-10, 10:56 AMHow could you be bored?Because you're not the first person to come on here and claim to have demonstrated relativity is flawed using algebra on the level expected in a beginners SR textbook. Your problems and arguments are not new and previously have been retorted and explained away by people here and in the relativity research community as a whole. This is exciting stuff.Depends your point of view. If you have only just come across relativity and all these weird experiments involving trains and flash lights and light cones then it might seem exciting and novel, even if you disagree with it. For those who have known relativity for years, if not decades, the said experiments and results are old news. More often than not a relativity nay-sayer is new to relativity and is still too entrenched in their Newtonian intuition and thinks that their comments and criticisms are novel or insightful or deep or advanced. Almost invariably they are none of those and the nay-sayer fails to realise just how little they have read and understood of relativity. If you aren't just a sock puppet of Jack_ then I suggest you look at threads he's started. He's the canonical example of what I've just said, someone with little or no knowledge, naive about his level of understanding (especially compared to professional researchers in relativity) and utterly unwilling to accept that perhaps he doesn't understand something he's only just read about. If you've made an honest attempt to learn some relativity and you're stuck on a few specific things then I'm sure people will be happy to help. If you're denouncing relativity because you haven't looked at it much and what you have looked at you've not bothered to think about then please don't let the door hit you on the way out. Motor Daddy05-12-10, 11:12 AMOne more fact to consider. If the observer on the train were to have two synchronized clocks at his midpoint position, and then place one clock on each end of the train, and return to his midpoint position, when he looks at the clocks, they will not read the same thing. That is because the train has a velocity, and the light from the clocks has to travel different distances to reach him. Different distances take light a different amount of time to travel. The clocks remained synchronized, but the observer refuses to believe it, until he verifies it when he retrieves both clocks and they show they are synchronized. That phenomena is due to the fact that the observer has a velocity. If the embankment observer does the same experiment with two of his own clocks, that phenomena will not occur for him. The clocks appear to remain synchronized from his midpoint position, because the embankment observer has a true zero velocity, and the clocks prove it, as the light from each clock travels the same distance to reach the observer. funkstar05-12-10, 11:21 AM...using algebra... I don't see any algebra, here... Janus5805-12-10, 11:45 AMOne more fact to consider. If the observer on the train were to have two synchronized clocks at his midpoint position, and then place one clock on each end of the train, and return to his midpoint position, when he looks at the clocks, they will not read the same thing. That is because the train has a velocity, and the light from the clocks has to travel different distances to reach him. Different distances take light a different amount of time to travel. The clocks remained synchronized, but the observer refuses to believe it, until he verifies it when he retrieves both clocks and they show they are synchronized. That phenomena is due to the fact that the observer has a velocity. If the embankment observer does the same experiment with two of his own clocks, that phenomena will not occur for him. The clocks appear to remain synchronized from his midpoint position, because the embankment observer has a true zero velocity, and the clocks prove it, as the light from each clock travels the same distance to reach the observer. I think we've struck your problem here. One of the postulates of Special Relativity holds that the speed of light is the same for all observers, as measured relative to themselves, regardless of their relative motion. Another way of putting it is that there is no test that the train observer can perform that will tell him whether or not it is the train or the embankment that is moving. He puts those clocks at the ends of the train and he will see them as reading the same time. They are an equal distance from him, and the light coming from both, traveling at the same speed relative to him, take the same amount of time to reach him. And this is why the lightning strikes are not simultaneous for him. He is an equal distance from either end of the train, where the lightning strikes occurred. The light from the strikes travels at the same speed, meaning that the time between each strike occurring and when he sees the light from it is the same. However, he sees the light from each strike at different times, meaning the strikes occurred at different times for him. Motor Daddy05-12-10, 11:57 AMAnother way of putting it is that there is no test that the train observer can perform that will tell him whether or not it is the train or the embankment that is moving. He puts those clocks at the ends of the train and he will see them as reading the same time. They are an equal distance from him, and the light coming from both, traveling at the same speed relative to him, take the same amount of time to reach him. There is no way the train observer will see the synchronized clocks as reading the same from his midpoint position, when the clocks are placed at each end of the train. The light from the clock on the front of the train will hit the observer first, making it appear that that clock is more advanced (in reality, less of a delay) than the rear clock, which is an illusion created because of the light travel time to impact the observer. Light speed is measured by how much distance the light travels, and how much time it takes to travel that distance. Janus5805-12-10, 01:32 PMThere is no way the train observer will see the synchronized clocks as reading the same from his midpoint position, when the clocks are placed at each end of the train. The light from the clock on the front of the train will hit the observer first, making it appear that that clock is more advanced (in reality, less of a delay) than the rear clock, which is an illusion created because of the light travel time to impact the observer. Light speed is measured by how much distance the light travels, and how much time it takes to travel that distance. The ends of the train are equal distances from the train observer. they are not moving with respect to the observer, so the time it takes for light to travel from them to the observer as far as the observer is concerned is the same. You seem to be laboring under the misconception that motion is absolute and that you can say which is moving, the train or embankment, in a way that everyone agrees to. This is not the case. All motion is relative, and anyone can make equal claim to being the one "at rest". This is a cornerstone of Relativity and is the foundation for all of its (experimentally confirmed) predictions. You can try to deny this, but you do so in the face of overwhelming evidence. Motor Daddy05-12-10, 01:50 PMThe ends of the train are equal distances from the train observer. they are not moving with respect to the observer, so the time it takes for light to travel from them to the observer as far as the observer is concerned is the same. Light travels independently of the train, at c. The time it takes the light to travel to the train observer's midpoint position is different for each strike. It is true that the train observer remains at the midpoint of the train, but when opposite ends of the train have light sources, and the lights are simultaneously activated (easily done with two lights and a common switch at the midpoint, activated by the observer), during the time it takes for light to travel the half length of the train, the observer also travels away from one light, and towards the other. That creates a situation that the light from one source has less distance to travel than the light from the other source, until it impacts the observer. You seem to be laboring under the misconception that motion is absolute and that you can say which is moving, the train or embankment, in a way that everyone agrees to. This is not the case. All motion is relative, and anyone can make equal claim to being the one "at rest". I've already showed why synchronized clocks will appear different to the observer on the train, which is a red flag as to the observer's actual velocity, unlike the embankment observer's actual zero velocity. You can not say the train is at rest and that it is actually the embankment that has a velocity (or any other combination of the two), due to the fact that the strikes occurred as the points lined up, and the light from the strikes impacted the embankment observer at the same time, and the train observer at different times. That is not a reversible situation. The points MUST be lined up. I explained the difference with the clock phenomena, which is also a true indicator of a zero velocity. rpenner05-12-10, 03:05 PMInability to comprehend relativity is the inability to put oneself intellectually into the shoes of another and working out the consequences. It seems to me that this belongs on the non-clinical side of a spectrum of sociopathic disorders. http://www.squidoo.com/the-sociopath-next-door Motor Daddy, The embankment is moving from: 1) The train's perspective 2) The detailed perspective of people in the next county 3) The obvious perspective of people in the antipodes. 4) The perspective of the Moon 5) The perspective of Mars 6) The perspective of the Sun 7) The perspective of the center of the Galaxy 8) The perspective of a hypothetical observer who observes no dipole anisotropy in the cosmic microwave background. So billions of people on Earth and nearly any other hypothetical observer attached to a massive object anywhere in the universe believe the embankment to be in a non-rest state of motion. Why do you prefer one observer's absolutely over the other's? Their local experiments do no reveal their state of motion and their situations differ only in degree. Indeed, if you are willing to replace the train and embankment with equal-mass planets counter-rotating and making a close approach, the relationship can be made as arbitrarily symmetrical as desired, and your choice of one observer other the other becomes not only unphysical but specious. Motor Daddy05-12-10, 03:48 PMCan we stick to Einstein's example? Are you saying that the light from the back of the train to the observer travels the same distance as the light from the front of the train to the observer? rpenner05-12-10, 04:24 PMI'm saying different folks will have different evidence-based viewpoints what the distance between events is, and that special relativity not only tells you that all inertial evidence-based viewpoints are equivalently valid but how to transform one viewpoint to another -- to place one observer in the other observer's shoes. Further, it works better as demonstrated by experiments as far back as 1859 than the previous notion of Galilean Relativity. http://www.sciforums.com/showthread.php?p=2039656#post2039656 Motor Daddy05-12-10, 04:38 PMI'm saying different folks will have different evidence-based viewpoints what the distance between events is, and that special relativity not only tells you that all inertial evidence-based viewpoints are equivalently valid but how to transform one viewpoint to another -- to place one observer in the other observer's shoes. Further, it works better as demonstrated by experiments as far back as 1859 than the previous notion of Galilean Relativity. The train observer's viewpoint of the strikes occurring at different times is invalid. That is simply impossible, as the points have to be lined up when the strikes occur, and there is only ONE point in time when they line up. In order for the strikes to have occurred at different times, the points would have to have two different reference points, and that simply isn't the case. The points were lined up when both strikes occurred. That is an indisputable fact for any observer in this universe. Sure, the lights hit the train observer at different times, but that is not when the strikes occurred, that is after the strikes occurred. rpenner05-12-10, 04:59 PMviewpoint ... is invalid. That is simply impossible there is only ONE point in time when they line up. that simply isn't the case. an indisputable fact for any observer in this universe.Nope. You are asserting absolute time but not arguing for it. Neither are you making an evidence-based argument. You may be confused about the content of Einstein's argument. All observers agree that events that happen at the same place and same time happen at the same place and at the same time. (The opposite would be maddening if not madness.) Coordinate-wise, these two things happen at the same coordinates in space an time. By a slight misuse of ordinary language we can refer to any quadruple of space-time coordinates as an "event" even if nothing happens there. But events that one observer sees happen in the same place at different times, another may say happen in different places with a non-zero distance between them for a second observer. (Even Galileo agreed with this.) And since 1859 we have experimental evidence that says two events which happen in different places may legitimately be seen by one observer to happen at the same time may equally as legitimately be seen by another observer to happen at different times. But while neither the distance between two events, \Delta x, nor the time interval between two events, \Delta t is seen the same by all observers, the spacetime interval \left( \Delta x \right)^2 - \left( c \Delta t \right)^2 between the two events is universally agreed upon. (You should be able to do the math that this statement also says all observers agree on the speed of light. ) Janus5805-12-10, 05:26 PMThe train observer's viewpoint of the strikes occurring at different times is invalid. That is simply impossible, as the points have to be lined up when the strikes occur, and there is only ONE point in time when they line up. In order for the strikes to have occurred at different times, the points would have to have two different reference points, and that simply isn't the case. The points were lined up when both strikes occurred. That is an indisputable fact for any observer in this universe. Sure, the lights hit the train observer at different times, but that is not when the strikes occurred, that is after the strikes occurred. All the points line up at one instant only according to an observer at rest with respect to the embankment. There is another effect of Relativity in play here" Length contraction. Anything with a motion relative to your own will be contracted in length along the line of motion. Thus, if the Train were at rest with the embankment, it would be noted that it longer than the distance between the points on the ground where the lightning strikes occurred. While it is moving, it is measured as contracted from the embankment, causing it to fit exactly between the strike points. However, from the train, it is the embankment that is contracted, and the distance between the strike points are closer together than the length of the train. So when the front end of the train reaches the forward strike point, the rear of the train has not yet reached it corresponding strike point yet. The simultaneous line up of all the points is not an indisputable fact for all observers. Janus5805-12-10, 05:52 PMI've already showed why synchronized clocks will appear different to the observer on the train, which is a red flag as to the observer's actual velocity, unlike the embankment observer's actual zero velocity. You can not say the train is at rest and that it is actually the embankment that has a velocity (or any other combination of the two), due to the fact that the strikes occurred as the points lined up, and the light from the strikes impacted the embankment observer at the same time, and the train observer at different times. That is not a reversible situation. The points MUST be lined up. I explained the difference with the clock phenomena, which is also a true indicator of a zero velocity. You haven't shown anything. You are making a claim based on how you believe things would behave. Your argument is basically " Relativity of Simultaneity is wrong because Simultaneity is absolute." Einstein uses a different set of postulates regarding the behavior of light. The concept of the Relativity of Simultaneity is a consequence of those postulates. Put simply, you are saying that the universe behaves in one way, while Relativity say it behaves in another. So, how do we know which is right? By performing an actual physical experiment. For example, we could take two synchronized clocks, but thema at the ends of a fast train and see if an observer sitting in the middle actually reads the same time on both or not. Now this particular experiment might not be easy to pull off, but there are other, easier experiments that can test the same thing. These experiment have been performed with increasing accuracy since the 1800's, and in every case, the result come down on the side of Relativity. So you have a choice: You can stick to your guns even though every piece of actual physical evidence in existence says that you are wrong. Or You can man-up, admit to being wrong, and try to wrap your mind around what it means to live in a Relativistic universe. AlphaNumeric05-12-10, 06:00 PMI don't see any algebra, here... I was speaking more generically, in that when a nay sayer makes his case its in terms of things which are pretty basic, they never phrase their arguments in terms of more advanced mathematics or physics. This suggests that they are either a) unaware there's more to relativity than just doing coordinate transformations, b) that they've only just come across relativity and so haven't advanced that far or c) they don't understand more advanced material, though often they'll claim the opposite. For instance, Jack_ throws around words like 'decidable' yet can't use the word 'proof' properly and all his algebra is 1st year stuff (at best). He claims to understand the posts I make in regards to bundles yet he never uses the much more powerful formalism of bundles to make his case. Why make life harder for yourself if you have the tools at your disposal to strengthen and streamline your argument? Unless, of course, he doesn't understand. If the observer on the train were to have two synchronized clocks at his midpoint position, and then place one clock on each end of the train, and return to his midpoint position, when he looks at the clocks, they will not read the same thing.This is false. As already explained to you such a result is in direct manifest contradiction to one of the postulates of SR and thus SR doesn't predict that the clocks will be different. And its a good job it does because that's in agreement with what experiments say! That phenomena is due to the fact that the observer has a velocity.Velocity with respect to whom? The ground? A plane in the sky? Jupiter? Motion is relative. If the train is on a perfectly smooth track so that it doesn't jiggle about when moving relative to the ground then alone straight horizontal lines of track the person on the train is in an inertial frame. He cannot work out his motion relative to the ground without looking out the window. His claim "I am in an inertial frame" is true and allows him to consider himself at rest. With the clocks being at rest with respect to him then their times will read the same from his point of view. Consider the case where all the windows are blacked out so the person on the train cannot get any information outside of the train's interior. By your logic he can work out his velocity by comparing clock times, that the amount the clock times disagree by allows you to find his speed. But this is not possible as the fact he's in an inertial frame means he's 'blind' to the motion of things outside of the train. He can't tell if the train is stationary or moving relative to the Earth, provided that motion is constant. If a specific speed could be obtained then it would be associated to a preffered frame and even if that were the case there's absolutely no reason to think it would be the ground's rest frame (particularly given the Earth is not in inertial motion, it rotates). There is no way the train observer will see the synchronized clocks as reading the same from his midpoint position, when the clocks are placed at each end of the train.You're wrong, as he's in an inertial frame. If you put two sync'd clocks at opposite corners of the room you're in right now and then sat in the middle you'd see them reading the same times, right? Right. After all you and they are stationary, the ground isn't moving underneath you, right? Wrong. They read the same times because you are stationary relative to them and in that frame you're at the midpoint between them. The motion of the Earth under your feet (or not) is irrelevant. After all, why pick Earth? What about the Moon, you're not stationary relative to the Moon, should the clocks tell you the relative motion between you and the Moon, as you claim it does between the train passenger and the Earth? Its the same setup, 2 clocks, an observer and some container within which they set which is moving relative to something else. Unless you believe the universe has a prefered frame and that frame is some point of ground on the Earth's surface your argument falls apart, independent of whether or not it passes experimental tests. Light travels independently of the train, at c. The time it takes the light to travel to the train observer's midpoint position is different for each strike. It is true that the train observer remains at the midpoint of the train, but when opposite ends of the train have light sources, and the lights are simultaneously activated (easily done with two lights and a common switch at the midpoint, activated by the observer), during the time it takes for light to travel the half length of the train, the observer also travels away from one light, and towards the other. That creates a situation that the light from one source has less distance to travel than the light from the other source, until it impacts the observer. You're describing the system from the point of view o an observer at rest with respect to the ground and made the mistake of thinking that the person on the train sees exactly the same sequence of events in the same time frames, which isn't the case. This is the counter-intuitive nature of special relativity, you've gotten stuck on the first big hurdle I'm afraid. Can we stick to Einstein's example? Sure, but I'd request you actually take the time to read his writings on the matter and then to learn the basics of special relativity because presently I'd say you lack the mathematical tools and conceptual understandings required to get your head around the counter-intuitive nature of the non-Euclidean geometry at play in relativity. As I said previously, look at threads started by the poster Jack_ (if you aren't he) and you'll find this setup has been beaten to death, full Lorentz transform examinations have been done, including diagrams, all in an effort to explain to Jack what we're now going to end up explaining to you. Are you saying that the light from the back of the train to the observer travels the same distance as the light from the front of the train to the observer? You really do need to spend some time finding out what SR is about, how its constructed and how it describes such systems, as you're currently displaying considerable naivety about it. If you don't know what SR actually says and why it says it it's a little unwise to try to argue that its wrong in what it says, particularly when those people you're trying to discuss SR with actually know some SR. That is simply impossible Given that comment we're now moving away from somewhat uninformed naivety to wilful ignorance and arrogance. You have simply utterly failed to understand relativity, either conceptually and quantitatively and given the pseudo-rhetorical question I quoted you saying just above suggests you haven't really made any effort to understand. Am I wrong in this evaluation, have you put in a fair chunk of time in order to try to understand SR? If not then its both silly and arrogant to say "Its obviously wrong, its impossible!" when you know full well you've not got a perfect understanding of the subject matter. That is an indisputable fact for any observer in this universe. And you know this how? Have you done your own experiments to test this premise? If so, what was it and when did you do it? If not then explain why you think you're justified in making what seems to be an unjustified claim. Those people who have done experiments in relation to relativity have found relativity to be vindicated, the issue of simultaneity and motion altering clocks is fundamental in the design of the GPS network, as they are basically clocks which shine light (ie radio signals) at observers from various places in the sky. So please explain why you think you have insight into the universe when you have not actually examined the universe yourself, you're ignoring those people who have and you haven't got much, if any, understanding of the models of said people. I'll suggest to you what I suggested to Jack (among other things), go learn how to construct and understand space-time diagrams in 1+1 dimensional special relativity. The choice in frames then can be expressed as different time slices of a worldline/light cone diagram. It'll make your mistake a bit clearer. Jack_05-12-10, 07:37 PMThe strikes occurred when the points were lined up. The points lined up once, not twice. Both strikes occurred at that time, which means simultaneously. The light impacted the train observer at different times from the front and rear. Light always travels at the same speed, independently of the frame. If the train observer were to have had a true zero velocity to consider himself "stationary", the lights would have impacted him at the same times, but they didn't. That means the observer had a velocity, which is clearly noted in the diagram with the arrow, and Einstein's own words. It is independent of frames, ie, the distance light travels is independent of the distance between the points of a single frame. Just because the observer sits midpoint of a frame doesn't mean light traveled the same distance to reach him. If the frame has a velocity the light has to travel a DIFFERENT distance, not the distance the observer in that frame measures. You are correct, but your proof skills are lacking. Jack_05-12-10, 07:43 PMI was speaking more generically, in that when a nay sayer makes his case its in terms of things which are pretty basic, they never phrase their arguments in terms of more advanced mathematics or physics. This suggests that they are either a) unaware there's more to relativity than just doing coordinate transformations, b) that they've only just come across relativity and so haven't advanced that far or c) they don't understand more advanced material, though often they'll claim the opposite. For instance, Jack_ throws around words like 'decidable' yet can't use the word 'proof' properly and all his algebra is 1st year stuff (at best). He claims to understand the posts I make in regards to bundles yet he never uses the much more powerful formalism of bundles to make his case. Why make life harder for yourself if you have the tools at your disposal to strengthen and streamline your argument? Unless, of course, he doesn't understand. This is false. As already explained to you such a result is in direct manifest contradiction to one of the postulates of SR and thus SR doesn't predict that the clocks will be different. And its a good job it does because that's in agreement with what experiments say! Velocity with respect to whom? The ground? A plane in the sky? Jupiter? Motion is relative. If the train is on a perfectly smooth track so that it doesn't jiggle about when moving relative to the ground then alone straight horizontal lines of track the person on the train is in an inertial frame. He cannot work out his motion relative to the ground without looking out the window. His claim "I am in an inertial frame" is true and allows him to consider himself at rest. With the clocks being at rest with respect to him then their times will read the same from his point of view. Consider the case where all the windows are blacked out so the person on the train cannot get any information outside of the train's interior. By your logic he can work out his velocity by comparing clock times, that the amount the clock times disagree by allows you to find his speed. But this is not possible as the fact he's in an inertial frame means he's 'blind' to the motion of things outside of the train. He can't tell if the train is stationary or moving relative to the Earth, provided that motion is constant. If a specific speed could be obtained then it would be associated to a preffered frame and even if that were the case there's absolutely no reason to think it would be the ground's rest frame (particularly given the Earth is not in inertial motion, it rotates). You're wrong, as he's in an inertial frame. If you put two sync'd clocks at opposite corners of the room you're in right now and then sat in the middle you'd see them reading the same times, right? Right. After all you and they are stationary, the ground isn't moving underneath you, right? Wrong. They read the same times because you are stationary relative to them and in that frame you're at the midpoint between them. The motion of the Earth under your feet (or not) is irrelevant. After all, why pick Earth? What about the Moon, you're not stationary relative to the Moon, should the clocks tell you the relative motion between you and the Moon, as you claim it does between the train passenger and the Earth? Its the same setup, 2 clocks, an observer and some container within which they set which is moving relative to something else. Unless you believe the universe has a prefered frame and that frame is some point of ground on the Earth's surface your argument falls apart, independent of whether or not it passes experimental tests. You're describing the system from the point of view o an observer at rest with respect to the ground and made the mistake of thinking that the person on the train sees exactly the same sequence of events in the same time frames, which isn't the case. This is the counter-intuitive nature of special relativity, you've gotten stuck on the first big hurdle I'm afraid. Sure, but I'd request you actually take the time to read his writings on the matter and then to learn the basics of special relativity because presently I'd say you lack the mathematical tools and conceptual understandings required to get your head around the counter-intuitive nature of the non-Euclidean geometry at play in relativity. As I said previously, look at threads started by the poster Jack_ (if you aren't he) and you'll find this setup has been beaten to death, full Lorentz transform examinations have been done, including diagrams, all in an effort to explain to Jack what we're now going to end up explaining to you. You really do need to spend some time finding out what SR is about, how its constructed and how it describes such systems, as you're currently displaying considerable naivety about it. If you don't know what SR actually says and why it says it it's a little unwise to try to argue that its wrong in what it says, particularly when those people you're trying to discuss SR with actually know some SR. Given that comment we're now moving away from somewhat uninformed naivety to wilful ignorance and arrogance. You have simply utterly failed to understand relativity, either conceptually and quantitatively and given the pseudo-rhetorical question I quoted you saying just above suggests you haven't really made any effort to understand. Am I wrong in this evaluation, have you put in a fair chunk of time in order to try to understand SR? If not then its both silly and arrogant to say "Its obviously wrong, its impossible!" when you know full well you've not got a perfect understanding of the subject matter. And you know this how? Have you done your own experiments to test this premise? If so, what was it and when did you do it? If not then explain why you think you're justified in making what seems to be an unjustified claim. Those people who have done experiments in relation to relativity have found relativity to be vindicated, the issue of simultaneity and motion altering clocks is fundamental in the design of the GPS network, as they are basically clocks which shine light (ie radio signals) at observers from various places in the sky. So please explain why you think you have insight into the universe when you have not actually examined the universe yourself, you're ignoring those people who have and you haven't got much, if any, understanding of the models of said people. I'll suggest to you what I suggested to Jack (among other things), go learn how to construct and understand space-time diagrams in 1+1 dimensional special relativity. The choice in frames then can be expressed as different time slices of a worldline/light cone diagram. It'll make your mistake a bit clearer. You're wrong, as he's in an inertial frame. If you put two sync'd clocks at opposite corners of the room you're in right now and then sat in the middle you'd see them reading the same times, right? Right. After all you and they are stationary, the ground isn't moving underneath you, right? Wrong. They read the same times because you are stationary relative to them and in that frame you're at the midpoint between them. The motion of the Earth under your feet (or not) is irrelevant. After all, why pick Earth? What about the Moon, you're not stationary relative to the Moon, should the clocks tell you the relative motion between you and the Moon, as you claim it does between the train passenger and the Earth? Its the same setup, 2 clocks, an observer and some container within which they set which is moving relative to something else. This is your best post yet to validate the OP's argument. The train observer is sitting with clocks at the flash points and they read the same time since they are in the frame. The embankment observer is sitting with co-located clocks at the flash points and they read the same time. Light is c in all frames and will take the same time to travel equidistances. So, each observer will see the strikes simultaneously as the OP contends and you just proved. Good Job!!! :bravo: Janus5805-12-10, 08:26 PMThis is your best post yet to validate the OP's argument. The train observer is sitting with clocks at the flash points and they read the same time since they are in the frame. The embankment observer is sitting with co-located clocks at the flash points and they read the same time. Light is c in all frames and will take the same time to travel equidistances. So, each observer will see the strikes simultaneously as the OP contends and you just proved. Good Job!!! :bravo: Nope, because in neither frame do the clocks at the end of the train read the same time when each lightning strikes them. The clocks at the ends of the train are synchronized in the train frame, but not in the embankment frame . Jack_05-12-10, 08:38 PMNope, because in neither frame do the clocks at the end of the train read the same time when each lightning strikes them. The clocks at the ends of the train are synchronized in the train frame, but not in the embankment frame . Seems you have having a problem taking a frame as stationary. Let's keep it simple. Both frames sync all their clocks. Do you understand this? We assume that this definition of synchronism is free from contradictions, and possible for any number of points; http://www.fourmilab.ch/etexts/einstein/specrel/www/ Now, the clocks in the train frame as stationary are all synched. The lightning flashes at equidistant points. Exercise: When will the light strike M'? Oh, Let's assume the distance to these synched clocks at light emission are a distance d. Pete05-12-10, 09:25 PMOne more fact to consider. If the observer on the train were to have two synchronized clocks at his midpoint position, and then place one clock on each end of the train, and return to his midpoint position, when he looks at the clocks, they will not read the same thing. Experiments say otherwise, MD - this is a variation on Michelson Morley. You're arguing with reality, dude. You're also arguing with the postulate of light invariance, which you clearly don't understand. Go to youtube and search for "relativity". Consider how you measure the speed of a real train. Do you need to consider the Earth's rotation or orbit? Why not? The invariance of light speed means that you measure the same speed without adjusting for you own movement, just like you can measure the speed of a train while standing on the ground without adjusting for the movement of the ground as the Earth turns and orbits. Pete05-12-10, 09:32 PMWe assume that this definition of synchronism is free from contradictions, and possible for any number of points; http://www.fourmilab.ch/etexts/einstein/specrel/www/ Now, the clocks in the train frame as stationary are all synched. *sigh* Jack, you're repeating long dead arguments. Like a broken record. http://redwing.hutman.net/~mreed/Assets/ferrouscranus.jpg Ferrous Cranus (http://redwing.hutman.net/~mreed/warriorshtm/ferouscranus.htm) Ferrous Cranus is utterly impervious to reason, persuasion and new ideas, and when engaged in battle he will not yield an inch in his position regardless of its hopelessness. Though his thrusts are decisively repulsed, his arguments crushed in every detail and his defenses demolished beyond repair he will remount the same attack again and again with only the slightest variation in tactics. Sometimes out of pure frustration Philosopher will try to explain to him the failed logistics of his situation, or Therapist will attempt to penetrate the psychological origins of his obduracy, but, ever unfathomable, Ferrous Cranus cannot be moved. Motor Daddy05-12-10, 09:56 PMAll the points line up at one instant only according to an observer at rest with respect to the embankment. There is another effect of Relativity in play here" Length contraction. Anything with a motion relative to your own will be contracted in length along the line of motion. Thus, if the Train were at rest with the embankment, it would be noted that it longer than the distance between the points on the ground where the lightning strikes occurred. While it is moving, it is measured as contracted from the embankment, causing it to fit exactly between the strike points. However, from the train, it is the embankment that is contracted, and the distance between the strike points are closer together than the length of the train. So when the front end of the train reaches the forward strike point, the rear of the train has not yet reached it corresponding strike point yet. The simultaneous line up of all the points is not an indisputable fact for all observers. The points in the example coincide with each other as Einstein clearly states. Are you saying Einstein didn't mean to say the points coincide? They do, the diagram shows that fact, and that is what Einstein states. What you are saying with the front of the train's point lining up, and the rear not yet lined up means that the observer either isn't in the middle of the length of the train, or that he is in the middle of that length, and that his midpoint doesn't line up with the embankment observers midpoint, as is also clearly stated in the diagram and text. Read chapter 9 and look at that diagram. Einstein makes perfectly clear the diagram and the wording. Motor Daddy05-12-10, 10:27 PMYou're wrong, as he's in an inertial frame. If you put two sync'd clocks at opposite corners of the room you're in right now and then sat in the middle you'd see them reading the same times, right? Right. After all you and they are stationary, the ground isn't moving underneath you, right? Wrong. They read the same times because you are stationary relative to them and in that frame you're at the midpoint between them. The motion of the Earth under your feet (or not) is irrelevant. After all, why pick Earth? What about the Moon, you're not stationary relative to the Moon, should the clocks tell you the relative motion between you and the Moon, as you claim it does between the train passenger and the Earth? Its the same setup, 2 clocks, an observer and some container within which they set which is moving relative to something else. If I put two synchronized clocks in a room and sit an equal distance apart from each, the only way I will see them as synchronized is if the room has an absolute zero velocity. You don't seem to understand the significance of light traveling independently of frames. Light travels a specific speed, regardless of the motion of any object it is traveling towards or away from. Light's speed is not dependent on another object, or even its own source. Light travels at c, period. If the room the clocks are in has an absolute velocity, even though the clocks are an equal distance from me, as measured in my frame, the light travels different distance to impact me, as I was "hastening" towards one light and moving away from the other light. The light from each clock will hit me at different times unless I have a true zero velocity. Pete05-12-10, 10:37 PMIf I put two synchronized clocks in a room and sit an equal distance apart from each, the only way I will see them as synchronized is if the room has an absolute zero velocity. You don't seem to understand the significance of light traveling independently of frames. MotorDaddy, the constancy of light says exactly the opposite of what you think it does, and experiments agree. The Michelson Morley experiment showed that the speed of light, measured on Earth without allowing for Earth's rotation or orbit, does not change over the course of a year. You're arguing with reality. Pete05-12-10, 10:53 PMThe points in the example coincide with each other as Einstein clearly states. Are you saying Einstein didn't mean to say the points coincide? They do, the diagram shows that fact, and that is what Einstein states. What you are saying with the front of the train's point lining up, and the rear not yet lined up means that the observer either isn't in the middle of the length of the train, or that he is in the middle of that length, and that his midpoint doesn't line up with the embankment observers midpoint, as is also clearly stated in the diagram and text. Read chapter 9 and look at that diagram. Einstein makes perfectly clear the diagram and the wording. Like I said earlier in the thread, that book by Einstein really isn't the best way to learn this stuff. It's a hundred years old, the language is archaic, and there have been a thousand better explanations written since then. It's not surprising that people find it hard to follow. In this particular case, the diagram illustrates a snapshot of the scenario "considered with reference to the railway embankment". It's not supposed to be an absolute picture of reality - that's really the whole point. In Einstein's words, it's "reality (considered with reference to the railway embankment)". So, Einstein said that the points coincide "As judged from the embankment." Not as judged from the train. Einstein could have done better by adding a diagram showing the train's reference frame. There are many better explanations that spell this out. Try here, for example: Relativity (http://einstein.byu.edu/~masong/htmstuff/Relativity2.html). Or here: Discovering the Relativity of Simultaneity (http://www.pitt.edu/~jdnorton/Goodies/rel_of_sim/index.html): http://www.pitt.edu/~jdnorton/Goodies/rel_of_sim/simult_1_anim.gif http://www.pitt.edu/~jdnorton/Goodies/rel_of_sim/Simultaneity_2_anim.gif Motor Daddy05-12-10, 11:07 PMMotorDaddy, the constancy of light says exactly the opposite of what you think it does, and experiments agree. The Michelson Morley experiment showed that the speed of light, measured on Earth without allowing for Earth's rotation or orbit, does not change over the course of a year. You're arguing with reality. The reality is, light has to travel different distances to impact the observer on the train. That is due to the train observer's velocity. It just so happens in Einstein's example that the embankment has a zero velocity, because Einstein set it up that way, unintentionally for sure. The embankment could have had a velocity and the train a velocity, and things would have been different, but that isn't how the example is set up. Light moves in space at c. Objects have relative velocities to the light. If light is at each end of a train, and an observer midway between the lights, the light from each source will travel different distances to reach the midpoint observer if the train has a velocity. The observer can declare all he want to be "inertial", but that only means "not accelerating", which doesn't say anything about his velocity. You can be inertial and have a zero velocity, or be inertial and have a .5c velocity. The velocity is what matters, as that determines how far the light has to travel to impact the observer. The light travel distance and time doesn't lie. Pete05-12-10, 11:18 PMThe reality is, light has to travel different distances to impact the observer on the train. That is due to the train observer's velocity. It just so happens in Einstein's example that the embankment has a zero velocity, because Einstein set it up that way, unintentionally for sure. The embankment could have had a velocity and the train a velocity, and things would have been different, but that isn't how the example is set up. Sorry, MD, you're all wrong. Absolute rest has been out of date since Galileo. Einstein's says that's reality "As judged from the embankment." The actual velocity of the embankment is arbitrary. It's certainly not supposed to be floating in space, unmoved by the Earth's orbit around the Sun, or the Sun's motion through the galaxy, or the galaxy's motion toward Andromeda. Where do you think Einstein says that the embankment is at absolute rest? Look. Here's a 1972 experiment that measured the speed of light in a laboratory (http://prl.aps.org/abstract/PRL/v29/i19/p1346_1) to within 1 m/s. They didn't adjust for the Earth's rotation or orbit. This measurement has been repeated and improved upon. No one has found it necessary to adjust for Earth's motion, yet they all get the same results. What does that tell you? Motor Daddy05-12-10, 11:36 PMSorry, MD, you're all wrong. Absolute rest has been out of date since Galileo. Einstein's says that's reality "As judged from the embankment." The actual velocity of the embankment is arbitrary. It's certainly not supposed to be floating in space, unmoved by the Earth's orbit around the Sun, or the Sun's motion through the galaxy, or the galaxy's motion toward Andromeda. Where do you think Einstein says that the embankment is at absolute rest? Einstein says that just as the points line up the strikes occur. The embankment observer is midway between the points, and the lights reach the embankment observer simultaneously. That can only happen if the observer has a zero velocity, for if he had a velocity, he would have moved closer to one light and away from the other, resulting in one light taking less time than if he were at a true zero velocity, and the other light taking more time than if he were at a zero velocity. Janus5805-12-10, 11:51 PMThe points in the example coincide with each other as Einstein clearly states. Are you saying Einstein didn't mean to say the points coincide? They do, the diagram shows that fact, and that is what Einstein states. What you are saying with the front of the train's point lining up, and the rear not yet lined up means that the observer either isn't in the middle of the length of the train, or that he is in the middle of that length, and that his midpoint doesn't line up with the embankment observers midpoint, as is also clearly stated in the diagram and text. Read chapter 9 and look at that diagram. Einstein makes perfectly clear the diagram and the wording. This is what Einstein says happens: This first animation shows events from the embankment frame: http://home.earthlink.net/~jparvey/sitebuildercontent/sitebuilderpictures/trainsimul1.gif And this animation shows the same events from the train's frame: http://home.earthlink.net/~jparvey/sitebuildercontent/sitebuilderpictures/trainsimul2.gif Note that in both animations, the front of the train and the right red dot coincide when the lightning strikes the dot, and the rear of the train and the left dot coincide when that lightning strikes. Also note that in both frames the light from both strikes reach the embankment observer simultaneously. However, this doesn't mean that both lightning strikes occurred at the same time in the train frame. Pete05-13-10, 12:43 AMEinstein says that just as the points line up the strikes occur. The embankment observer is midway between the points, and the lights reach the embankment observer simultaneously. That can only happen if the observer has a zero velocity, for if he had a velocity, he would have moved closer to one light and away from the other, resulting in one light taking less time than if he were at a true zero velocity, and the other light taking more time than if he were at a zero velocity. Now you're just repeating yourself, MD. Did you think about that experiment? How do you think those guys consistently measured the speed of light without taking the Earth's motion into account? AlphaNumeric05-13-10, 01:27 AMThis is your best post yet to validate the OP's argument.Jack, why do you quote the entire post of mine and then quote again a specific paragraph you want to respond to? Either don't quote the entire post or just quote the relevant bit. You know, like everyone else does! I think even you can grasp the quote function, please try it. So, each observer will see the strikes simultaneously as the OP contends and you just proved. I like how you just jumped from what I said to the conclusion I said precisely the opposite. Obviously you 'proof skills' need improvement, as well as MD's. Maybe the two of you could take a class together. Managed to put your physics where your mouth is and submitted to a journal yet Jack? Though not. Motor Daddy05-13-10, 06:40 AMNote that in both animations, the front of the train and the right red dot coincide when the lightning strikes the dot, and the rear of the train and the left dot coincide when that lightning strikes. Also note that in both frames the light from both strikes reach the embankment observer simultaneously. However, this doesn't mean that both lightning strikes occurred at the same time in the train frame. Albert Einstein (1879–1955). Relativity: The Special and General Theory. 1920. IX. The Relativity of Simultaneity UP to now our considerations have been referred to a particular body of reference, which we have styled a “railway embankment.” We suppose a very long train travelling along the rails with the constant velocity v and in the direction indicated in Fig. 1. People travelling in this train will with advantage use the train as a rigid reference-body (co-ordinate system); they regard all events in reference to the train. Then every event which takes place along the line also takes place at a particular point of the train. Also the definition of simultaneity can be given relative to the train in exactly the same way as with respect to the embankment. As a natural consequence, however, the following question arises: 1 Are two events (e.g. the two strokes of lightning A and B) which are simultaneous with reference to the railway embankment also simultaneous relatively to the train? We shall show directly that the answer must be in the negative. FIG. 1. 2 When we say that the lightning strokes A and B are simultaneous with respect to the embankment, we mean: the rays of light emitted at the places A and B, where the lightning occurs, meet each other at the mid-point M of the length A —> B of the embankment. But the events A and B also correspond to positions A and B on the train. Let M' be the mid-point of the distance A —> B on the travelling train. Just when the flashes 1 of lightning occur, this point M' naturally coincides with the point M, but it moves towards the right in the diagram with the velocity v of the train. If an observer sitting in the position M’ in the train did not possess this velocity, then he would remain permanently at M, and the light rays emitted by the flashes of lightning A and B would reach him simultaneously, i.e. they would meet just where he is situated. Now in reality (considered with reference to the railway embankment) he is hastening towards the beam of light coming from B, whilst he is riding on ahead of the beam of light coming from A. Hence the observer will see the beam of light emitted from B earlier than he will see that emitted from A. Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightning flash B took place earlier than the lightning flash A. We thus arrive at the important result: 3 Events which are simultaneous with reference to the embankment are not simultaneous with respect to the train, and vice versa (relativity of simultaneity). Every reference-body (co-ordinate system) has its own particular time; unless we are told the reference-body to which the statement of time refers, there is no meaning in a statement of the time of an event. 4 Now before the advent of the theory of relativity it had always tacitly been assumed in physics that the statement of time had an absolute significance, i.e. that it is independent of the state of motion of the body of reference. But we have just seen that this assumption is incompatible with the most natural definition of simultaneity; if we discard this assumption, then the conflict between the law of the propagation of light in vacuo and the principle of relativity (developed in Section VII) disappears. 5 We were led to that conflict by the considerations of Section VI, which are now no longer tenable. In that section we concluded that the man in the carriage, who traverses the distance w per second relative to the carriage, traverses the same distance also with respect to the embankment in each second of time. But, according to the foregoing considerations, the time required by a particular occurrence with respect to the carriage must not be considered equal to the duration of the same occurrence as judged from the embankment (as reference-body). Hence it cannot be contended that the man in walking travels the distance w relative to the railway line in a time which is equal to one second as judged from the embankment. 6 Moreover, the considerations of Section VI are based on yet a second assumption, which, in the light of a strict consideration, appears to be arbitrary, although it was always tacitly made even before the introduction of the theory of relativity. 7 Note 1. As judged from the embankment. In your animations the reference points don't line up when the strikes occur. As I said before, this example could be redone with the train observer at the midpoint of the train having a switch that activates two lights, one on each end of the train. When the observer activates the switch, the lights simultaneously emit light, and the lights each hit the observer at different times. The observer will refuse to believe the lights were activated simultaneously, even though there was only one switch and he operated it. That phenomena is due to his velocity and would not occur if he didn't posses that velocity. Also, what do you think the directional arrow represents, and what is the direction in reference to? Motor Daddy05-13-10, 07:17 AMNow you're just repeating yourself, MD. Did you think about that experiment? How do you think those guys consistently measured the speed of light without taking the Earth's motion into account? The speed of light has nothing to do with another object's motion. The speed of light is simply the distance the light travels and the duration of travel, as compared to the standard second. If you measured the light coming from the sun in a spherical way, how big would the light sphere be after 1 second? ~186,000 mile radius? Correct. But what if during that one second the sun traveled? Does that change the diameter of the 1 second light sphere? NO! It only means the sun is no longer in the center of that 1 second light sphere. The sun's motion has nothing to do with the speed of light. Janus5805-13-10, 07:19 AM"Then every event which takes place along the line also takes place at a particular point of the train." If you look carefully at the animations, you will note that when a flash reaches any given point of the embankment, the same point of the train is adjacent to it [i]in both animations. For example, the left flash reaches the rightmost red dot when the train observer reaches that dot in both animations. My animation fulfills this requirement Also the definition of simultaneity can be given relative to the train in exactly the same way as with respect to the embankment." Earlier is the same book he gives the definition of simultaneity that he refers to here. It is this: If you are standing exactly at the midpoint between two events and you see them at the same time, then for you those events are simultaneous. It is this definition that also applies relative to the train. If the train observer is halfway between the ends of the train and see events at the end of the train at the same time ,hen those events are simultaneous for the train observer. 2 If an observer sitting in the position M’ in the train did not possess this velocity, then he would remain permanently at M, and the light rays emitted by the flashes of lightning A and B would reach him simultaneously, i.e. they would meet just where he is situated. Now in reality [color=red](considered with reference to the railway embankment)[\color] Which is repeated with this note at the bottom of the passage: Note 1. As judged from the embankment. Look, I've read this passage. I have the book. You are misinterpreting the meaning of his statements. In your animations the reference points don't line up when the strikes occur. As I said before, this example could be redone with the train observer at the midpoint of the train having a switch that activates two lights, one on each end of the train. When the observer activates the switch, the lights simultaneously emit light, and the lights each hit the observer at different times. The observer will refuse to believe the lights were activated simultaneously, even though there was only one switch and he operated it. That phenomena is due to his velocity and would not occur if he didn't posses that velocity. This your example, the light would come on simultaneously in the train frame and the train observer would see them simultaneously. However they would not come on simultaneously for the observer on the embankment, nor would he see the lights simultaneously. All this version does is change which frame the lights are simultaneous in. Pete05-13-10, 07:30 AMThe speed of light has nothing to do with another object's motion. The speed of light is simply the distance the light travels and the duration of travel, as compared to the standard second. But don't you see? In the lab, the light receiver moves with the Earth between between sending the light and receiving it. The experimenters did not allow for that motion, and yet they still got a consistent measurement. You can't argue with reality, MD. Motor Daddy05-13-10, 07:32 AMEarlier is the same book he gives the definition of simultaneity that he refers to here. It is this: If you are standing exactly at the midpoint between two events and you see them at the same time, then for you those events are simultaneous. It is this definition that also applies relative to the train. If the train observer is halfway between the ends of the train and see events at the end of the train at the same time ,hen those events are simultaneous for the train observer. Just because two snowballs hit you simultaneously doesn't mean the snowballs traveled the same distance or speed. Two lights hitting you at the same time says nothing about the simultaneity of the emission of those lights. This your example, the light would come on simultaneously in the train frame and the train observer would see them simultaneously. Absolutely not! What you are saying is that the lights will always impact the midpoint observer simultaneously, regardless of the motion of the train. That is an absurd statement! Motor Daddy05-13-10, 07:44 AMBut don't you see? In the lab, the light receiver moves with the Earth between between sending the light and receiving it. The experimenters did not allow for that motion, and yet they still got a consistent measurement. You can't argue with reality, MD. I'll ask again: If you measured the light coming from the sun in a spherical way, how big would the light sphere be after 1 second? ~186,000 mile radius? Correct. But what if during that one second the sun traveled? Does that change the diameter of the 1 second light sphere? NO! It only means the sun is no longer in the center of that 1 second light sphere. The sun's motion has nothing to do with the speed of light. Pete05-13-10, 07:59 AMI'll ask again: If you measured the light coming from the sun in a spherical way, how big would the light sphere be after 1 second? ~186,000 mile radius? Correct. But what if during that one second the sun traveled? Does that change the diameter of the 1 second light sphere? NO! It only means the sun is no longer in the center of that 1 second light sphere. The sun's motion has nothing to do with the speed of light. You're not really trying to get it, are you? Look, imagine the experimenters are on the train. They know the length of the train, they have synchronized clocks at each end. A light flashes at one end, it is received at the other. The experimenters measure the time elapsed between light emitted and light received using their synchronized clocks, and they measure the distance travelled from the length of the train. They divide distance by time to get the speed. Note that they don't concern themselves over whether the train (or the Earth) is moving or not. Now this isn't exactly how the experiment was done, of course. In practice there are many devilish details built up from previous experiments. But the principle is close enough. Motor Daddy05-13-10, 08:05 AMYou're not really trying to get it, are you? Look, imagine the experimenters are on the train. They know the length of the train, they have synchronized clocks at each end. A light flashes at one end, it is received at the other. The experimenters measure the time elapsed between light emitted and light received using their synchronized clocks, and they measure the distance travelled from the length of the train. They divide distance by time to get the speed. Note that they don't concern themselves over whether the train (or the Earth) is moving or not. Now this isn't exactly how the experiment was done, of course. In practice there are many devilish details built up from previous experiments. But the principle is close enough. So no matter what, the distance the light travels in the train experiment is always the same, regardless of the train's motion? I'll ask another way, if you do the test when the train is going 60 MPH, will the distance the light travels be the same as when you do the experiment when the train is going 120 MPH? Pete05-13-10, 08:09 AMSo no matter what, the distance the light travels in the train experiment is always the same, regardless of the train's motion? In the train's reference frame, yes. I'll ask another way, if you do the test when the train is going 60 MPH, will the distance the light travels be the same as when you do the experiment when the train is going 120 MPH? How far do you drive to work? Does it depend on which way the Earth is moving? Motor Daddy05-13-10, 08:25 AMIn the train's reference frame, yes. The distance the light travels is not related to a frame. You didn't comment on the light sphere. Do you agree the light sphere will have a ~186,000 mile radius 1 second after emission? Does the motion of that source change the distance traveled? How far do you drive to work? Does it depend on which way the Earth is moving? Relate that to the train. As far as the train observer is concerned, the light always travels from one end of the train to the other. If that distance is 100 feet then certainly the train observer can say the light traveled from point a to point b, which is 100 feet in his frame. BUT, the train observer must understand that the distance light travels is not measured against his own frame. The distance light travels is not compared to a frame. Going back to the light sphere, if light is emitted from a source in space, the sphere will have a radius of ~186,000 miles after 1 sec of travel, regardless of the motion of the source. Pete05-13-10, 09:02 AMThe distance the light travels is not related to a frame. That's what relativity is all about, MD. All measurement of distance and time are relative to some arbitrary rest reference. Relate that to the train. As far as the train observer is concerned, the light always travels from one end of the train to the other. If that distance is 100 feet then certainly the train observer can say the light traveled from point a to point b, which is 100 feet in his frame. BUT, the train observer must understand that the distance light travels is not measured against his own frame. What reference frame do you think it's measured against, MD? The Earth? The Sun? The galaxy? It's Relativity. Relative to a reference frame. Any reference frame. Get used to it. Going back to the light sphere, if light is emitted from a source in space, the sphere will have a radius of ~186,000 miles after 1 sec of travel, regardless of the motion of the source. That's right, rabbit. But we're talking about moving observers, not moving sources. You didn't answer the question about driving to work. If you live 1 mile from your office, that's how far you drive, right? Motor Daddy05-13-10, 09:21 AMThat's right, rabbit. But we're talking about moving observers, not moving sources. We are talking about the speed of light, which is measured in the distance and time the light travels, which is not dependent on an observer. You didn't answer the question about driving to work. If you live 1 mile from your office, that's how far you drive, right? I answered the question, related to the train. Yes, if you measured 1 mile on the Earth's surface, then it is one mile on the Earth's surface. That doesn't mean light always takes the same amount of time to go from the starting point to the ending point, regardless of the Earth's velocity. You can be going 60 MPH on the highway in your car, and strangely enough, if the car 20 feet in front of you also travels 60 MPH, you will not increase or decrease the distance between the cars. Both have a speed of 60 MPH, and yet, the distance between remains the same. HMMMMMMM, let's see if light does the same. I turn on my headlights, and during the time it takes for the light to travel from my car to the car 20 feet in front of me, the car in front of me moves forward, away from the light, so the light has to travel more than 20 feet to reach the car. Does the light travel 20 feet just because the distance between the cars remained 20 feet? No. Pete05-13-10, 09:43 AMThat doesn't mean light always takes the same amount of time to go from the starting point to the ending point, regardless of the Earth's velocity. That is exactly what Einstein is going on about, MD and exactly what we find in practice. You can be going 60 MPH on the highway in your car, and strangely enough, if the car 20 feet in front of you also travels 60 MPH, you will not increase or decrease the distance between the cars. Both have a speed of 60 MPH, and yet, the distance between remains the same. HMMMMMMM, let's see if light does the same. I turn on my headlights, and during the time it takes for the light to travel from my car to the car 20 feet in front of me, the car in front of me moves forward, away from the light, so the light has to travel more than 20 feet to reach the car. Does the light travel 20 feet just because the distance between the cars remained 20 feet? No. How far does it go, MD? How fast it the Earth, the Sun, and the Galaxy moving? Using the cars as as refernce, the light travels just 20 feet. That's relativity. Motor Daddy05-13-10, 09:54 AMHow far does it go, MD? How fast it the Earth, the Sun, and the Galaxy moving? Using the cars as as refernce, the light travels just 20 feet. That's relativity. If light has to "chase" an object in absolute space, it takes more time to "catch it" than if the object is moving towards the light, obviously. Light always travels at c. How much time it takes for the light to reach another object is only dependent on the absolute motion of that other object, and the distance between the source and other object at emission. Pete05-13-10, 10:03 AMIf light has to "chase" an object in absolute space, it takes more time to "catch it" than if the object is moving towards the light, obviously. Light always travels at c. How much time it takes for the light to reach another object is only dependent on the absolute motion of that other object, and the distance between the source and other object at emission. Again with the absolute motion. Go read up on the Michelson Morley experiment, and stop arguing with reality. rpenner05-13-10, 10:08 AMIf light has to "chase" an object in absolute space, it takes more time to "catch it" than if the object is moving towards the light, obviously. Obviously, but assumes absolute space unnecessarily as this is trivially true in Galilean and Special Relativity also, and works with any two objects at any two speeds provided the event where the objects coincide is in the future. i.e. You aren't doing physics but a trivial description of motion. Light always travels at c.Better to write: light is always observed to travel at c, independent of the relative motion between observer and source and observer and destination, and independent of the measurements of any other observer who may also be in relative motion with the original observer and yet will still measure the speed as c. How much time it takes for the light to reach another object is only dependent on the absolute motion of that other object, Again, you say absolute, but cannot possibly measure absolute.And in fact the only physical examples you give are of relative motion, not absolute. and the distance between the source and other object at emission. ... as measured by a particular observer. It's only when you consider the viewpoint of a different observer that the core of Relativity can be tested. Motor Daddy05-13-10, 10:10 AMAgain with the absolute motion. Go read up on the Michelson Morley experiment, and stop arguing with reality. And again, the radius of the light sphere increases at the rate of ~186,000 miles per second. It doesn't matter what the motion of the source is, or what the motion of any other object or observer in the universe is. The radius of the light sphere increases at the rate of ~186,000 miles per second, period. Pete05-13-10, 10:23 AMAnd again, the radius of the light sphere increases at the rate of ~186,000 miles per second. It doesn't matter what the motion of the source is, or what the motion of any other object or observer in the universe is. The radius of the light sphere increases at the rate of ~186,000 miles per second, period. Relative to what, MD? You think there's some absolute rest frame, that light moves at c onl relative to "absolute space". Guess what - when people look for "absolute space", it's not there. Any reference frame is as good as another. You're arguing with reality, and it's really getting very boring. Do you want a discussion that involves some learning, or do you just want to dictate how the universe should work? Do you think it will listen? Motor Daddy05-13-10, 10:30 AMRelative to what, MD? You think there's some absolute rest frame, that light moves at c onl relative to "absolute space". Guess what - when people look for "absolute space", it's not there. Any reference frame is as good as another. You're arguing with reality, and it's really getting very boring. Do you want a discussion that involves some learning, or do you just want to dictate how the universe should work? Do you think it will listen? I'm not saying how the universe should work, I'm saying that light travels a specific distance in a specific duration, independent of observers or objects. Space means simply volume. The universe is an infinite volume. In that volume there are objects of mass, each with a motion. Light travels in the dimensions of the volume, regardless of what the motion of each mass is. Pete05-13-10, 10:45 AMMD, if the moving train observer sets off two flashes at the front and rear of the train at the same time, and he measured the speed of those using his moving rulers, you assert that he would measure the front-to-back light to go faster, right? You say that the front-to-rear light would go from one end of his meter stick in less time than the rear-to-front flash. Right? So, if we do the same experiment on Earth using Earth-based rulers, and if Earth is moving in absolute space, then we should also measure light to go faster in one direction than another because our rulers are moving, right? Motor Daddy05-13-10, 10:54 AMMD, if the moving train observer sets off two flashes at the front and rear of the train at the same time, and he measured the speed of those using his moving rulers, you assert that he would measure the front-to-back light to go faster, right? You say that the front-to-rear light would go from one end of his meter stick in less time than the rear-to-front flash. Right? So, if we do the same experiment on Earth using Earth-based rulers, and if Earth is moving in absolute space, then we should also measure light to go faster in one direction than another because our rulers are moving, right? If a moving train has two lights, one at the front and one at the rear, and the lights emit light simultaneously, the light from each light sphere will have the same radius when they meet. If the train had a velocity during that time of light travel, the sources will not be an equal distance from the meeting point when they meet. Two light spheres are being emitted, the velocity of the sources has no affect when those spheres will meet. Pete05-13-10, 11:01 AMDo you agree that my previous post is an accurate statement of your position? Motor Daddy05-13-10, 11:05 AMDo you agree that my previous post is an accurate statement of your position? No, and I explained why in my response. Light speed is not dependent on an observer's motion. Two light spheres a specific distance apart will always meet in the same amount of time if emitted simultaneously, regardless of the motion of the sources after emission. Pete05-13-10, 11:16 AMYour previous post is consistent with what I said. Try it this way: The train observer is trying to figure out whether the train is moving, and in which direction. They have a light, a detector, and some very precise timing equipment. They measure the time it takes light to travel from the front of the train to the back, and from the back of the train to the front. What do they measure? Same times? Different times? Motor Daddy05-13-10, 11:21 AMYour previous post is consistent with what I said. Try it this way: The train observer is trying to figure out whether the train is moving, and in which direction. They have a light, a detector, and some very precise timing equipment. They measure the time it takes light to travel from the front of the train to the back, and from the back of the train to the front. What do they measure? Same times? Different times? Same times. They are only measuring the speed of light, not the train's motion. Pete05-13-10, 11:33 AMSame times. Are you sure? Great if you are, but it doesn't seem to mesh with what you were arguing earlier. So, Light going from the front to the back takes the same time as light going from the back to the front? If two light flashes started at the same time, one from the front and one from the rear, you say that they would also reach the other end of the train at the same time? Is that what an embankment observer would see as well if they could peek in the window as the train went past? Janus5805-13-10, 11:39 AMI'm not saying how the universe should work, Yes. you are, because your very argument is contrary to real physical observation of the universe shows. I'm saying that light travels a specific distance in a specific duration, independent of observers or objects. That distance and duration is observer(frame) dependent. Space means simply volume. The universe is an infinite volume. In that volume there are objects of mass, each with a motion. Light travels in the dimensions of the volume, regardless of what the motion of each mass is. You need a frame of reference to measure any motion. And there is no preferred frame of reference. Every one of those masses can make an equal claim to being at rest. But the masses themselves are not important. only the frame of reference (you don't need a physical object or observer for a frame of reference. There are an infinite number of frames of reference, all with different velocities with respect to each other, and each one measures the speed of light as 186,00 mps relative to itself. to use your Sun analogy. For someone for which the Sun is moving, the Sun leaves the center of the expanding sphere of light, but for the Sun, it always remains at the center of the sphere of light that it emitted. You can howl and scream how this is Absurd or impossible all you want, this is how the universe works, As has been verified by actual experiment. Motor Daddy05-13-10, 11:49 AMAre you sure? Positive. They are only measuring the speed of light. Light going from the front to the back takes the same time as light going from the back to the front? Light travels at c, regardless of "direction." If two light flashes started at the same time, one from the front and one from the rear, you say that they would also reach the other end of the train at the same time? They are measuring the speed of light. The speed of light is the same from the front to the back or the back to the front. Is that what an embankment observer would see as well if they could peek in the window as the train went past? The embankment observer would see them measuring the speed of light, and laugh at them. :) Pete05-13-10, 12:00 PMSo, our train observer in the middle of the carriage can have a light flash at each end, pass him in the middle at the same time, and continue to the other end, regardless of the train's motion. Excellent. I'm glad we agree, and I'm glad you've changed your mind since post 42 when you suggested that this could only happen for an observer with zero absolute velocity. Good night. Motor Daddy05-13-10, 12:03 PMYou need a frame of reference to measure any motion. You can not measure motion while it is happening. The time has to have already elapsed for you to know the distance that was traveled. There is no motion at that point, the stop watch has already stopped. funkstar05-13-10, 12:05 PMIf light has to "chase" an object in absolute space, it takes more time to "catch it" than if the object is moving towards the light, obviously. Nature doesn't agree. End of story. (Why does this forum keep attracting cranks?) Motor Daddy05-13-10, 12:08 PMSo, our train observer in the middle of the carriage can have a light flash at each end, pass him in the middle at the same time, and continue to the other end, regardless of the train's motion. Excellent. I'm glad we agree, and I'm glad you've changed your mind since post 42 when you suggested that this could only happen for an observer with zero absolute velocity. Good night. What makes you think that if the lights were emitted simultaneously that they would always meet the observer simultaneously? That can only happen if the observer has a true zero velocity. Changing the observers velocity means he is "hastening" towards one light while moving away from the other, which mean the two lights will not impact the observer simultaneously, as he has changed positions since the lights were emitted. Good night. While you sleep, you realize time keeps ticking, correct? I mean, time actually continues to pass even though you are not observing it, believe it or not. ;) Pete05-13-10, 12:37 PMWhat makes you think that if the lights were emitted simultaneously that they would always meet the observer simultaneously? MD, you're contradicting yourself. You just agreed that for the train observer with unknown velocity, if two light flashes started at the same time, one from the front and one from the rear, they would also reach the other end of the train at the same time because the speed of light is fixed. Now, you're saying that no, the front-to-rear light reaches the middle of the train before the rear-to-front light. Make up your mind. Let's try once again: The train observer (who doesn't know whether the train is moving) is standing in the middle of the train. They use synchronized clocks to trigger simultaneous light flashes from the front and rear of the train. They measure how long it takes the light flashes to reach them in the middle of the train. What do they measure for the two flashes? Same times? Different times? Can the train observer use these measurements to measure their velocity in absolute space? Motor Daddy05-13-10, 01:53 PMLet's try once again: You did not say anything about synchronized clocks. You are changing the scenario and then saying I changed my answer. Tisk tisk. The train observer (who doesn't know whether the train is moving) is standing in the middle of the train. They use synchronized clocks to trigger simultaneous light flashes from the front and rear of the train. So let's talk about the term "synchronized" shall we? You mean, two clocks were at the center of the train, reading and keeping the same time, correct? OK. Now, you place one clock on each end of the train and return to the center of the train, correct? When the clock's light from each clock reaches the center of the train, do the clocks appear to remain synchronized, or does one clock appear to be ahead of the other? They measure how long it takes the light flashes to reach them in the middle of the train. They measure the time it takes the light to reach them at their current position on the train? So if the train did posses a velocity, that midpoint position would continuously change relative to the speed of light, correct?? Motor Daddy05-13-10, 02:08 PM(Why does this forum keep attracting cranks?) Cranks?? Is that the part of the internal combustion engine that converts reciprocating motion into a more useful rotary motion? And how would you measure the motion of said "crank?" How about we measure the revolutions per minute, you know, using the standard second as the interval of time. So we measure the RPM of the crank at a constant rotational velocity at say 3,000 RPM. Now, we need to know more about that motion, as the crank could be turning a 3000 lb-ft load at 3,000 RPM, or it could be turning a 30 lb-ft load at 3,000 RPM. The term RPM doesn't quite describe the motion in its entirety. Luckily, torque is here to save the day. Yes, that's right, we can use the unit of measure called horsepower (HP) to measure the power by simply measuring the RPM and the torque on the crank at that RPM. You see, the unit of measure of HP is equal to 550 ft-lbs of work per second, or 33,000 ft-lb of work per minute. So, if you have a 1 lb load on the end of a 1 ft bar (1 lb-ft of torque) and you spin it 1 RPM, the 1 lb load travels 6.2832 ft per minute, which is 6.2832 ft-lb of work per minute. Since 1 HP is 33,000 ft-lb of work per minute, a 1 lb load spinning (33,000/6.2832) 5252 RPM is equal to 1 HP, or HP=torque*RPM/5252. ;) Pete05-13-10, 02:15 PMYou did not say anything about synchronized clocks. You are changing the scenario and then saying I changed my answer. Tisk tisk. I'm spelling it out for you because I can't seem to make myself understood. You quoted me in post 73: "If two light flashes started at the same time, ..." I mentioned synchronized clocks to be absolutely sure that you understand what "at the same time" means. If you think that's changing the scenario, then I don't know what you're thinking. So let's talk about the term "synchronized" shall we? You mean, two clocks were at the center of the train, reading and keeping the same time, correct? OK. Now, you place one clock on each end of the train and return to the center of the train, correct? When the clock's light from each clock reaches the center of the train, do the clocks appear to remain synchronized, or does one clock appear to be ahead of the other? You can put it that way if you like. I'd rather stick with light flashes emitted at the same time, like we established, but whatever floats your boat. They measure the time it takes the light to reach them at their current position on the train? The time for light from the front, and the time for light from the back. Do they measure the same times, or different times? If different, which time is shorter? What does this tell the train observer (if anything) about their absolute motion? So if the train did posses a velocity, that midpoint position would continuously change relative to the speed of light, correct?? Sorry, I don't know what you mean. Motor Daddy05-13-10, 02:28 PMYou can put it that way if you like. I'd rather stick with light flashes emitted at the same time, like we established, but whatever floats your boat. Which way, that the clocks appear to remain synchronized from the midpoint of the train, or that they appear to be out of sync? Which one? Motor Daddy05-13-10, 02:30 PMSorry, I don't know what you mean. If the train were to have a velocity, and two lights simultaneously emitted, would the train observer at the midpoint remain at the point where the two light spheres will meet? Pete05-13-10, 03:03 PMWhich way, that the clocks appear to remain synchronized from the midpoint of the train, or that they appear to be out of sync? Which one? The light flashes are emitted at the same time. The clocks are synchronized. No one needs to look at the clocks, they just trigger a timer. Have the guy do whatever process you need to satisfy yourself that he can accurately measure the time taken for light to get from each end to the middle. Pete05-13-10, 03:09 PMIf the train were to have a velocity, and two lights simultaneously emitted, would the train observer at the midpoint remain at the point where the two light spheres will meet? No. But, relativity says that the question of whether the train "has a velocity" is arbitrary. It's a matter of choice, not an absolute thing. But, right now I'm trying to establish what you think. So, the train observer measures: The time for light to to go fromt he front of the train to the middle, and the time for light to got from the back. of the train to the middle. Do they measure the same times, or different times? If different, which time is shorter? What does this tell the train observer (if anything) about their absolute motion? Motor Daddy05-13-10, 03:09 PM:bugeye: The light flashes are emitted at the same time. The clocks are synchronized. I don't care what they look like. You don't care what they look like? Certainly you do, as when you look at the night sky you do realize that what you are seeing is the past? So you are not concerned with redshift or blue shifted light, it's all the same to you? Come on, you're pulling my leg, of course you care. Do the clocks appear to be synchronized when viewed from the midpoint of the train? Also, if the observer initially synchronized 3 clocks, put one at each end and kept one for himself at the midpoint, if the train had a zero velocity would the clocks at each end of the train agree with the midpoint observer's clock from his perspective, and also, and most importantly, if the midpoint observer viewed the end clocks as being out of sync with each other, would that mean the train had a velocity? Pete05-13-10, 03:38 PM:bugeye: Sorry MD, the clocks are internal to the flash apparatus. You can't see a reading with the cover closed. The guy sets the timers when they are together. The flashes are set to fire at a specific future time. Is that enough for you? Why is it not sufficient to say that the flashes are emitted simultaneously? Motor Daddy05-13-10, 03:40 PM:bugeye: Sorry MD, the clocks are internal to the flash apparatus. You can't see a reading with the cover closed. The guy sets the timers when they are together. The flashes are set to fire at a specific future time. Is that enough for you? Why is it not sufficient to say that the flashes are emitted simultaneously? I want to know your answers to my questions. I edited the previous post with an additional question. Can you please just answer my questions to the best of your ability? Pete05-13-10, 03:57 PMThis started with me asking you a simple question. You're side tracking. So, the train observer measures: The time for light to to go from the front of the train to the middle, and the time for light to go from the back of the train to the middle. Do they measure the same times, or different times? If different, which time is shorter? What does this tell the train observer (if anything) about their absolute motion? Motor Daddy05-13-10, 04:02 PMThis started with me asking you a simple question. You're side tracking. So, the train observer measures: The time for light to to go from the front of the train to the middle, and the time for light to go from the back of the train to the middle. Do they measure the same times, or different times? If different, which time is shorter? What does this tell the train observer (if anything) about their absolute motion? Pete, I have answered all your questions to the best of my ability. I expect you to do the same. Please, if you want to continue an honest conversation then please answer the questions to the best of your ability, in all honesty. You are beating around the bush because you know what I am getting at, and it doesn't help your case. As a matter of fact, it blows your ship out of the water! :) Pete05-13-10, 04:12 PMMD, right now I'm not exploring what I think relativity says. I want to know what you think. I honestly don't know. it seems to me you've said two completely opposite things, and I want to resolve what you meant. If you think it's important, you tell me. Do the clocks look like they're synchronized? When you've got that off your chest, how about addressing the simple question I posed more than ten posts ago? The train observer measures: The time for light to to go from the front of the train to the middle, and the time for light to go from the back of the train to the middle. Do they measure the same times, or different times? If different, which time is shorter? What does this tell the train observer (if anything) about their absolute motion? Motor Daddy05-13-10, 04:23 PMMD, right now I'm not exploring what I think relativity says. I want to know what you think. I honestly don't know. it seems to me you've said two completely opposite things, and I want to resolve what you meant. If you think it's important, you tell me. Do the clocks look like they're synchronized? First and foremost, light takes time to travel, regardless how small the distance. Light does not travel instantly. Given that fact, the observer at the midpoint of the train with his clock will not see the end clocks as reading the same as his, even though he just synchronized them and knows the clocks keep accurate time. It is simply a matter of distance, the end clocks are a distance away from the midpoint clock. An observer at the midpoint can not see his clock as reading the same as the end clocks. Point two, and most importantly, if the two end clocks appear to be out of sync to the midpoint observer, the train MUST have a velocity. The ONLY way the two end clocks will appear to be in sync with each other, to the midpoint observer, is if the train has an actual zero velocity. Being inertial only means "not accelerating" and that says nothing about the velocity of an object, for an object could be inertial and have a velocity. Three clocks all synchronized placed in a train, one at each end and one at the midpoint of the train with an observer. If the train has a velocity the two end clocks will appear to the midpoint observer as being out of sync with each other. Cut and dry. Pete05-13-10, 04:28 PMLovely. So (according to you) we can measure absolute motion by measuring light signals (or looking at synchronized clocks). So, what is this absolute motion? If it can be measured, then surely anyone with a good laboratory and laser can find measure how fast the Earth is moving through absolute space, right? Motor Daddy05-13-10, 04:36 PMLovely. So (according to you) we can measure absolute motion by measuring light signals (or looking at synchronized clocks). So, what is this absolute motion? If it can be measured, then surely anyone with a good laboratory and laser can find measure how fast the Earth is moving through absolute space, right? I'll leave that to the experts, which doesn't include me. ;) Jack_05-13-10, 05:22 PMSorry, MD, you're all wrong. Absolute rest has been out of date since Galileo. Einstein's says that's reality "As judged from the embankment." The actual velocity of the embankment is arbitrary. It's certainly not supposed to be floating in space, unmoved by the Earth's orbit around the Sun, or the Sun's motion through the galaxy, or the galaxy's motion toward Andromeda. Where do you think Einstein says that the embankment is at absolute rest? Look. Here's a 1972 experiment that measured the speed of light in a laboratory (http://prl.aps.org/abstract/PRL/v29/i19/p1346_1) to within 1 m/s. They didn't adjust for the Earth's rotation or orbit. This measurement has been repeated and improved upon. No one has found it necessary to adjust for Earth's motion, yet they all get the same results. What does that tell you? Look. Here's a 1972 experiment that measured the speed of light in a laboratory (http://prl.aps.org/abstract/PRL/v29/i19/p1346_1) to within 1 m/s. They didn't adjust for the Earth's rotation or orbit. This measurement has been repeated and improved upon. No one has found it necessary to adjust for Earth's motion, yet they all get the same results. What does that tell you? It tells me you have no idea what you are talking about. http://relativity.livingreviews.org/Articles/lrr-2003-1/ Look at chapter 5. You will note a nercessary Sagnac correction based on the rotation of the earth of GPS would be inaccurate. So, there needs to be an adjustment and you are wrong. Jack_05-13-10, 05:26 PMLovely. So (according to you) we can measure absolute motion by measuring light signals (or looking at synchronized clocks). So, what is this absolute motion? If it can be measured, then surely anyone with a good laboratory and laser can find measure how fast the Earth is moving through absolute space, right? Here you are again. The reason we can detect distance star light aberration is because the earth moves relative to a constant speed of light in space. In fact, this was used to calculate the speed of the earth's orbit around the sun by testing the earth's relative motion to this constant absolute light speed. Pete05-13-10, 05:44 PMSo, there needs to be an adjustment and you are wrong. There was no adjustment, and you are *still* wrong about the Sagnac effect. The reason we can detect distance star light aberration is because the earth moves relative to a constant speed of light in space. ...and still making shit up. We can measure stellar aberration because the Earth's motion relative to any given star changes over the course of a year. Pete05-13-10, 05:58 PMI'll leave that to the experts, which doesn't include me. ;) Well, the experts have found that it can't be done. Try as you might, you can't mesaure light in a laboratory and work out your absolute speed - the result is always what you'd expect to get if Earth was at absolute rest. What do you make of that? rpenner05-13-10, 06:11 PMLook at chapter 5. You will note a nercessary Sagnac correction based on the rotation of the earth of GPS would be inaccurate. So, there needs to be an adjustment and you are wrong. You also fail to understand when the Sagnac effect \Delta t = \oint \frac{2 \bf{v} \cdot d\bf{s}}{c^2 - \left( \frac{\bf{v} \cdot d\bf{s}}{| d\bf{s} | } \right)^2} does apply. Nor do you work out any of the details. http://sciforums.com/showthread.php?p=2526994#post2526994 For atomic clocks in satellites, it is most convenient to consider the motions as they would be observed in the local ECI [inertial] frame. Then the Sagnac effect becomes irrelevant. (The Sagnac effect on moving ground-based receivers must still be considered.) The Sagnac effect does not affect the speed of light, it affects roundtrip time in an experiment when part of the light path is in relative motion, such as a rotating arrangement of mirrors or a fiber optic conveyor belt or when the receiver of a GPS system is in motion relative to the assumed ECI frame. Neil Ashby writes that by working in a coordinate frame which does not rotate every 24 hours, the Sagnac effect of a path about the Earth (hundreds of nanoseconds) need not be accounted for. In the same way, a conventional light speed measurement which uses linear paths that enclose no area have zero Sagnac effect, even if they are rotated or carried about. Jack_05-13-10, 06:37 PMYou also fail to understand when the Sagnac effect \Delta t = \oint \frac{2 \bf{v} \cdot d\bf{s}}{c^2 - \left( \frac{\bf{v} \cdot d\bf{s}}{| d\bf{s} | } \right)^2} does apply. Nor do you work out any of the details. http://sciforums.com/showthread.php?p=2526994#post2526994 Glad to see you take a stand. Your integral is logically equivalent to taking the path length * ( 1/(c-v) - ( 1/(c+v) ) If you compare your answer to 2πr( 1/(c-v) - ( 1/(c+v) ) you will find the answers to be the same. Hence, you are of the crowd that believes an enclosed path is a necessary condition for sagnac just by the way the equations looks. Looks can be deceiving. When you write the equation correctly, my way the nature of sagnac is revelaed. A closed path is not necessary. Let's check GPS to see you are wrong. The Sagnac effect can be regarded as arising from the relativity of simultaneity in a Lorentz transformation to a sequence of local inertial frames co-moving with points on the rotating earth. http://relativity.livingreviews.org/Articles/lrr-2003-1/ See chapter 2 and 5. You will note, an enclosed path does not exist between the satellite and the GPS unit. So, you are wrong. The Sagnac effect does not affect the speed of light, it affects roundtrip time in an experiment when part of the light path is in relative motion, such as a rotating arrangement of mirrors or a fiber optic conveyor belt or when the receiver of a GPS system is in motion relative to the assumed ECI frame. Let's get some terms for your training. There is the speed of light in space and there is the measured speed of light. I was talking about the measured speed of light. Pete's proposed experiment claimed light measured c in all directions regardless of the speed of the rotating earth. That was the context. These terms can be tricky. I posted GPS which proves light is not always measured c in the rotating earth frame as he contended. Hence, his experiment is false and it is a well know physics experiment that is stupid and false. I assume you realize the space-time coords sent to the ground based receiver are in the rotating earth frame. Neil Ashby writes that by working in a coordinate frame which does not rotate every 24 hours, the Sagnac effect of a path about the Earth (hundreds of nanoseconds) need not be accounted for. In the same way, a conventional light speed measurement which uses linear paths that enclose no area have zero Sagnac effect, even if they are rotated or carried about. This is correct. But, you did not read it completely. If ALL coords of GPS where registered in the non-rotating earth frame, meaning an artificial frame of an earth that does not rotate, then and only then would sagnac be ignored. That is absolutely true. This is similar to the sagnac experiment in the lab that does not rotate. It does not see sagnac. So if all coords of the rotating frame in the lab were converted to the stationary non-rotating frame, then sagnac would not be picked up. Oh, by so doing, the conversion to that frame would inherently contain the sagnac adjustment by using c+v and c-v to convert to that non-rotating frame. rpenner05-13-10, 06:45 PMHa ha. Get banned. Jack_05-13-10, 06:51 PMHa ha. Get banned. Why because you stepped over your head? How should that affect me? Let's continue the discussion. Motor Daddy05-13-10, 08:50 PMWell, the experts have found that it can't be done. Try as you might, you can't mesaure light in a laboratory and work out your absolute speed - the result is always what you'd expect to get if Earth was at absolute rest. What do you make of that? The Earth came from the Sun, what do you make of that? Pete12-12-10, 06:27 PMMD, you said that you would leave the measurement of absolute velocity to the experts. The experts have done the measurements using your proposed method, and always measured zero. A basic rule of common sense is that if the map disagrees with the ground, the ground is rong. In science, this means that if reality (ie real experiments) disagree with the theory, then the theory is wrong. Reality disagrees with your concept of space and time. Your concept is wrong. Motor Daddy12-13-10, 09:32 AMMD, you said that you would leave the measurement of absolute velocity to the experts. The experts have done the measurements using your proposed method, and always measured zero. A basic rule of common sense is that if the map disagrees with the ground, the ground is rong. In science, this means that if reality (ie real experiments) disagree with the theory, then the theory is wrong. Reality disagrees with your concept of space and time. Your concept is wrong. Really? Then how do you explain light travel time being different if measured from front to rear than rear to front? Are you implying that a train has two different lengths? Your basic map rule is wrong. If the map disagrees with the ground, the map is wrong. Pete12-13-10, 04:59 PMReally? Then how do you explain light travel time being different if measured from front to rear than rear to front? :rolleyes: You still haven't done the exercises or looked up any experiments, I see. The difference in travel time measurements can be anything at all depending on the synchronization of the clocks at each end of the plane. The problem is that you can never be sure if your clocks are correctly synchronized or not. Any synchronization method you use will give different results depending on your velocity. But you're avoiding one question by raising another. I think that means you're unable to address this issue: You claim that absolute velocity is measureable by simple experiments. The experts have done the experiments. Absolute velocity is always measured to be zero. That's reality, MD. If the map disagrees with the ground, the map is wrong. If you think the ground is different, then show me the actual experiments that prove it. Pete12-13-10, 05:04 PMPete, your math will use time dilation and length contraction. Those only exist in Einstein's world. I don't live in Einstein's world, I live in reality. So you don't believe in time dilation and length contraction, either? MD, you have the greatest research tool in the world at your fingertips. Use it. Experimental basis of Special Relativity (http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/SR/experiments.html) Why do you think you know what reality is when you haven't even looked? AlexG12-13-10, 10:40 PMSo you don't believe in time dilation and length contraction, either? MD, you have the greatest research tool in the world at your fingertips. Use it. Experimental basis of Special Relativity (http://www.xs4all.nl/~johanw/PhysFAQ/Relativity/SR/experiments.html) Why do you think you know what reality is when you haven't even looked? MD is a long time Einstein and Relativity denier. He has a truely amazing ability to ignore experimental results in favor of his own 'reasoning'. Tach12-14-10, 12:13 AMReally? Then how do you explain light travel time being different if measured from front to rear than rear to front? It is very easy, you can find the explanation in many introductory books. In one direction, the light chases the end of the train car, so the equation of motion is: c*t1=v*t1+L where L=length of the train car, v=speed of the train car. So t1=L/(c-v) In the opposite direction, the light front is moving heads on towards the end of the car, so: c*t2+v*t2=L i.e. t2=L/(c+v) The same thing happens in the case of light moving E-W or W-E around the Earth: c*t1=L+R*omega*t1 in the W>E direction c*t2+R*omega*t2=L in the E->W direction So, t1>t2 in both cases, while light speed is isotropic. arfa brane12-14-10, 01:01 AMDude, the distance light travels is determined by the length of the train. If the train has a constant length, then light travels the SAME distance; front to rear = rear to front. The train's velocity is irrelevant. At least that's my explanation for "why the travel times are different", they AREN'T different, OK? Of course, this is only true if you're an observer on the train; it isn't true for an external observer. I surmise that MD's confusion is related to his habit of making continual and arbitrary change of coordinates. You can't get away with that sort of carry-on, it just isn't scientific. rpenner12-14-10, 03:52 AMTechnically, changing your premises in midstream is not logical, a prerequisite for math or physics. Tach12-14-10, 10:53 AMDude, the distance light travels is determined by the length of the train. If the train has a constant length, then light travels the SAME distance; front to rear = rear to front. The train's velocity is irrelevant. At least that's my explanation for "why the travel times are different", they AREN'T different, OK? This is textbook physics, the train speed is KEY, if you don't know it, you can always try learning it instead of posting stupid stuff. Of course, this is only true if you're an observer on the train; it isn't true for an external observer. I surmise that MD's confusion is related to his habit of making continual and arbitrary change of coordinates. You can't get away with that sort of carry-on, it just isn't scientific. MD posts a whole slew of other ineptitudes but you aren't the right person to correct him. arfa brane12-14-10, 12:04 PMThis is textbook physics, the train speed is KEY, if you don't know it, you can always try learning it instead of posting stupid stuff. Why is the speed of the train "key", and to what? I think you're the one posting stupid stuff. But by all means, explain what the train's velocity has to do with the time it takes a beam of light to travel the length of the train. Go on, you know you want to. Tach12-14-10, 12:06 PMWhy is the speed of the train "key", and to what? I think you're the one posting stupid stuff. But by all means, explain what the train's velocity has to do with the time it takes a beam of light to travel the length of the train. Go on, you know you want to. You can't read some simple math, can you? arfa brane12-14-10, 12:09 PMLost for words, are we? Not doing very well with that "explanation" either, the one you can't provide because you haven't got a clue? Tach12-14-10, 12:12 PMLost for words, are we? Not doing very well with that "explanation" either, the one you can't provide because you haven't got a clue? No, because you are an idiot. Even Motor Daddy understands this subject a little better than you. arfa brane12-14-10, 12:21 PMKeep making those ridiculous noises, it's funny in a desperate sort of way, dude. You really don't have a clue do you? phyti12-14-10, 07:56 PMDude, the distance light travels is determined by the length of the train. If the train has a constant length, then light travels the SAME distance; front to rear = rear to front. The train's velocity is irrelevant. At least that's my explanation for "why the travel times are different", they AREN'T different, OK? Of course, this is only true if you're an observer on the train; it isn't true for an external observer. I surmise that MD's confusion is related to his habit of making continual and arbitrary change of coordinates. You can't get away with that sort of carry-on, it just isn't scientific. The times are different, but Einstein defined them for the inertial observer to be equal! "We have not defined a common time'' for A and B, for the latter cannot be defined at all unless we establish by definition that the time'' required by light to travel from A to B equals the time'' it requires to travel from B to A. Let a ray of light start at the A time'' from A towards B, let it at the B time'' be reflected at B in the direction of A, and arrive again at A at the A time'' ." 1905 paper, par 2. arfa brane12-14-10, 08:04 PMThe times are different, but Einstein defined them for the inertial observer to be equal!The observer on the train sees light take the same time to traverse the train in either direction, which is a consequence of light having a constant speed. He assumes the latter is true. "We have not defined a common time'' for A and B, for the latter cannot be defined at all unless we establish by definition that the time'' required by light to travel from A to B equals the time'' it requires to travel from B to A. Let a ray of light start at the A time'' from A towards B, let it at the B time'' be reflected at B in the direction of A, and arrive again at A at the A time'' ." What this is about is forming a rigorous definition of time and more importantly, distance (as traveled by light), in fact identical distances if the A and B have zero relative velocity. Motor Daddy12-14-10, 10:15 PMThe times are different, but Einstein defined them for the inertial observer to be equal! "We have not defined a common time'' for A and B, for the latter cannot be defined at all unless we establish by definition that the time'' required by light to travel from A to B equals the time'' it requires to travel from B to A. Let a ray of light start at the A time'' from A towards B, let it at the B time'' be reflected at B in the direction of A, and arrive again at A at the A time'' ." 1905 paper, par 2. Which has total disregard for the train's velocity. Einstein uses a totally fabricated system not in keeping with the concept of elapsed time and simultaneity. Maybe it's easier to use, and it does have some benefits such as GPS etc, but it is wrong for one main reason, he has total disregard for the inertial object's velocity. AlexG12-14-10, 11:15 PM. Maybe it's easier to use, and it does have some benefits such as GPS etc, but it is wrong for one main reason, he has total disregard for the inertial object's velocity. So ignore real world observation, experimentation and technology in order to maintain your delusion. Motor Daddy12-15-10, 07:36 AMSo ignore real world observation, experimentation and technology in order to maintain your delusion. Real world observation is that all objects have velocity. D H12-15-10, 09:07 AMWith respect to what? Motor Daddy12-15-10, 09:23 AMWith respect to what? Light travel times. Tach12-15-10, 11:16 AMEinstein uses a totally fabricated system not in keeping with the concept of elapsed time and simultaneity. Einstein has been dead for 65 years. Yet, his science has survived the most stringent testing. The fact you don't understand it doesn't falsify it. Maybe it's easier to use, and it does have some benefits such as GPS etc, but it is wrong for one main reason, he has total disregard for the inertial object's velocity. Tough, eh? phyti12-15-10, 07:15 PMThe observer on the train sees light take the same time to traverse the train in either direction, which is a consequence of light having a constant speed. He assumes the latter is true. This is a consequence of the clock synch method. What this is about is forming a rigorous definition of time and more importantly, distance (as traveled by light), in fact identical distances if the A and B have zero relative velocity. We know he's defining a standard for time and simultaneity so moving observers descriptions relate to the same events. The point to be made was, it's a convention/definition, not a fact about a physical process. An official could issue a decree that the moon is only half as far away, but the moon would not comply. In par. 3, he uses closing speeds in defining the transformation equations,so he knows the outbound and inbound times are different for light transit times, but ignores it to preserve constant light speed. AlexG12-15-10, 08:25 PMThis is a consequence of the clock synch method. This has nothing to do with clocks being in synch. This is what the observer observes, not what is measured. phyti12-17-10, 11:32 AMThis has nothing to do with clocks being in synch. This is what the observer observes, not what is measured. It is seldom the case that simultaneous perception of light signals means simultaneous occurrences of the events that produce them. Viewing the night sky, no one would conclude that the light left all sources at the same time. If the rear flash ocurred before the front flash, they could arrive simultaneously at the midpoint of the train. The person at the midpoint would resolve this by polling the clocks at both ends with a light signal. The clocks would read the same, but only because they were previously synchronized using the SR method. This could easily be proved by not synchronizing the train clocks after attaining speed. The clocks would still have earth synched time, but a different rate. When the flashes ocurr, a clock at each flash would indicate different times. Pete05-08-11, 05:03 AMThe topic of this thread was brought up in another (Light at Light speed), and I'm bringing it back here to avoid a major sidetrack in that thread. Here's a deal for you: We're considering two mathematical worlds: Newton's world and Einstein's world. You think that Newton's world is a better match for the real world than Einstein's. I think that Einstein's world is a better match. If you agree that only actual measurements of the real world (ie experiments) can decide who is right, then I'll show you the numbers in Einstein's world, one small step at a time, so you can point out any problems. Deal? How about this. We have a deal, but first you prove to me a relativity of simultaneity exists before you start using it in your method of calculations. Show me your numbers of Chapter 9 and prove to me that a relativity of simultaneity actually exists as Einstein claims it does. Prove it! Show me the numbers! I'll start from the assumptions that: the embankment is at rest light travels at c with respect to the embankment then show that in the mathematical world of time dilation and length contraction: The train observer can't tell how fast he's going. His best measurements tell him he's at rest. He can't synchronize his clocks with the embankment clocks. His best synchronization methods make his clocks out of sync with the embankment clocks The clocks he synchronized as well as he possibly could tell him that the lightning strike at the front of the train happened before the lightning strike at the back of the train. I'll go one step at a time, and wait for your questions and corrections before proceeding. In return, I expect that if I am able to do this to your satisfaction, then you will agree: that Einstein's world is a logically consistent world, and that if actual measurements in the real world match Einstein's world better than your own conceptual model, then your own conceptual model is wrong at relativistic speeds. Agreed? Motor Daddy05-08-11, 05:19 PMI'll start from the assumptions that: the embankment is at rest light travels at c with respect to the embankment then show that in the mathematical world of time dilation and length contraction: The train observer can't tell how fast he's going. His best measurements tell him he's at rest. He can't synchronize his clocks with the embankment clocks. His best synchronization methods make his clocks out of sync with the embankment clocks The clocks he synchronized as well as he possibly could tell him that the lightning strike at the front of the train happened before the lightning strike at the back of the train. I'll go one step at a time, and wait for your questions and corrections before proceeding. In return, I expect that if I am able to do this to your satisfaction, then you will agree: that Einstein's world is a logically consistent world, and that if actual measurements in the real world match Einstein's world better than your own conceptual model, then your own conceptual model is wrong at relativistic speeds. Agreed? How did you come to the conclusion the embankment was at rest? "At rest" compared to what? Pete05-08-11, 06:26 PMIt's an assumption, a premise. Not a conclusion. Every calculation I make will be based on the premises that the embankment is actually at rest, and that light actually travels at c relative to the embankment. To recap and add clarification: Assumptions: The embankment is at rest Light travels at c with respect to the embankment Clocks on the embankment are synchronized with each other The train observer knows that light travels at c with respect to something at rest The train observer doesn't know that the embankment is at rest The train observer doesn't know that the embankment clocks are synchronized The train observer has precise clocks, but he doesn't know if they're synchronized Moving clocks run slowly by the Lorentz factor Moving rulers are shorter in the direction of motion by the Lorentz factor Are these premises acceptable to you? All my calculations must be perfectly consistent with these premises. From these premises, I believe I can prove that: The train observer can't tell how fast he's going. His best measurements tell him he's at rest. His best measurements tell him that the speed of light is c with respect to the train. He can't synchronize his clocks. His best synchronization methods make his clocks out of sync with the embankment clocks The clocks he synchronized as well as he possibly could tell him that the lightning strike at the front of the train happened before the lightning strike at the back of the train. Motor Daddy05-08-11, 06:39 PMIt's an assumption, not a conclusion. Every calculation I make will be based on the assumption that the embankment is actually at rest, and that light actually travels at c relative to the embankment. At rest compared to what? You say it's at rest. What do you mean by that? Pete05-08-11, 07:12 PMAt rest compared to what? You say it's at rest. What do you mean by that? I will assume that the embankment is absolutely at rest. Motor Daddy05-08-11, 07:13 PMI will assume that the embankment is absolutely at rest. I'll ask you again, what do you mean when you say the embankment is at rest? Pete05-08-11, 07:16 PMI don't know how to be any clearer. What is ambiguous about "the embankment is absolutely at rest"? Motor Daddy05-08-11, 07:17 PMI don't know how to be any clearer. What is ambiguous about "the embankment is absolutely at rest"? Do you mean the embankment has a zero velocity? Pete05-08-11, 07:19 PMYes. Motor Daddy05-08-11, 07:19 PMYes. Compared to what? How would you determine if the embankment had a zero velocity or a 1,000 m/s velocity? Pete05-08-11, 07:23 PMThat's a problem that the train observer will indeed have to address in order to determine the velocity of the train. I'm starting the with assumption that the embankment is at rest. I'm taking it as given. But perhaps you would you like to suggest a method of determining the embankment's velocity? Motor Daddy05-08-11, 07:31 PMThat's a problem that the train observer will indeed have to address in order to determine the velocity of the train. The train observer has the same problem as you have. You say the embankment has a zero velocity, and the train observer says the train has a zero velocity? So before you or an observer on the train (or any observer in the universe) can make any statements about motion they first need to know their own motion. I've noted and you've made it clear you have no way of actually knowing whether the embankment has a zero velocity or not, you are simply guessing, and there is only 1 chance out of an infinite amount of possibilities that you are correct. I'm starting the with assumption that the embankment is at rest. I'm taking it as given. You have no way of knowing or testing, you just start from a random assumption and work from there, is that correct? What is your concept of the embankment's velocity? What is that zero velocity relative to, in your mind? Pete05-08-11, 07:39 PMI'm happy to use your method of determining absolute velocity: The observer on the train measures the time it takes light to go from the rear of the train car to the front of the train car, which is 11.9915 meters in length in the train frame. Light takes .00000004 seconds to travel the length of the train. That means the absolute velocity of the train is 4,958 m/s. Motor Daddy05-08-11, 07:42 PMI'm happy to use your method of determining absolute velocity: Good, so you'll also be using it for the measure of the train's velocity as well, correct? Pete05-08-11, 07:55 PMYes, we can use that method to determine the train's absolute velocity. The train observer has limited knowledge (they don't know what clocks are synchronized), but they will try to use that method as best they can with the available tools. If two clocks are: - synchronized with each other - sitting at each end of an x length ruler And if a light signal leaves goes from one clock the the other: - leaving when the first clock reads t0 - arriving when the second clock reads t1 Then the measured velocity of the ruler and clocks in the direction of the light signal is given by: v = c - x/(t1-t0) Pete05-08-11, 08:03 PMOf course, the train observer will also have to account for the length contraction of their rulers and time dilation of their clocks. This will be included in the numbers, when you're happy with the starting assumptions. Motor Daddy05-08-11, 08:05 PMThe train observer will use that method as best they can with the available tools. If two clocks are: - synchronized with each other - sitting at each end of an x length ruler And if a light signal leaves goes from one clock the the other: - leaving when the first clock reads t0 - arriving when the second clock reads t1 Then the measured velocity of the ruler and clocks in the direction of the light signal is given by: v = c - x/(t1-t0) So let's do a sample to see if we're on the same sheet of music. v=(ct-l)/t It takes .1 seconds for light to travel the length of a 1 meter long stick. I say the stick has a 299,792,448 m/s velocity, what say you? Motor Daddy05-08-11, 08:06 PMOf course, the train observer will also have to account for the length contraction of their rulers and time dilation of their clocks. This will be included in the numbers, when you're happy with the starting assumptions. We'll get to that.... Pete05-08-11, 08:13 PMSo let's do a sample to see if we're on the same sheet of music. v=(ct-l)/t It takes .1 seconds for light to travel the length of a 1 meter long stick. I say the stick has a 299,792,448 m/s velocity, what say you? Yes, that's right. It takes .1 absolute seconds for light to travel the length of a stick that is 1 absolute meter long moving at 299792448 m/s. Motor Daddy05-08-11, 08:16 PMYes, that's right. It takes .1 absolute seconds for light to travel the length of a stick that is 1 absolute meter long moving at 299792448 m/s. Good, we're making progress. So if the distance between A and B on the embankment is 10 meters, and you say the embankment has a zero velocity, how much time does it take light to travel from A to B? Pete05-08-11, 08:29 PMIf A and B aren't moving, t = d/c = 33.36 nanoseconds Obviously. Is this really necessary? I'm not trying to pull the wool over your eyes. If I do something dodgy in the calculations, you can stop me and thrash out the details then. Motor Daddy05-08-11, 08:35 PMIf A and B aren't moving, t = d/c = 33.36 nanoseconds Obviously. Is this really necessary? I'm not trying to pull the wool over your eyes. If I do something dodgy in the calculations, you can stop me and thrash out the details then.Uh, one small correction, maybe you made a typo? v=(ct-l)/t so t = l/(c-v) You agree? Pete05-08-11, 08:40 PMYes, t=l/(c-v) for absolute t, l, and v. But you said A and B were on the embankment, which I understood to mean they were at rest. If not, then please specify their velocity. (Edit - missed a "/") Motor Daddy05-08-11, 08:46 PMYes, t=l(c-v) for absolute t, l, and v. But you said A and B were on the embankment, which I understood to mean they were at rest. You still made a typo? You need to be more precise, Pete. t = l/(c-v) Let's do a sample with the embankment having a velocity, to be sure. It's 10 meters between A and B on the embankment. The embankment has a 1,000 m/s velocity. How much time did it take light to travel from A to B? I say .000000033356520785191951666614863989887 seconds, what say you? Pete05-08-11, 08:49 PMYou still made a typo? Thanks. Let's do a sample with the embankment having a velocity, to be sure. It's 10 meters between A and B on the embankment. The embankment has a 1,000 m/s velocity. How much time did it take light to travel from A to B? I say .000000033356520785191951666614863989887 seconds, what say you? I agree. Motor Daddy05-08-11, 08:52 PMThanks. I agree. So then you agree with all my numbers in this quote? Let's look at Einstein's train thought experiment in Chapter 9. The Relativity of Simultaneity. Einstein, Albert. 1920. Relativity: The Special and General Theory. Einstein conveniently forgot to put numbers to the thought experiment, so let's do it for him, shall we? The observer on the train measures the time it takes light to go from the rear of the train car to the front of the train car, which is 11.9915 meters in length in the train frame. Light takes .00000004 seconds to travel the length of the train. That means the absolute velocity of the train is 4,958 m/s. The observer on the tracks measures the time it takes light to travel the distance between two clocks on the track, which is 1 meter. It takes light .0000000033356409519815204957557671447492 seconds to travel the distance, which means the track has an absolute zero velocity. It is 10 meters from A to B on the train in the train frame, and 10 meters from A to B on the embankment in the embankment frame. Both observers are at the midpoint between A and B in their respective frames. Lightening strikes A and B as the two points on the train coincide with the two points on the embankment. Light takes .000000016678204759907602478778835723746 seconds for each light from A and B to strike the embankment observer. The embankment observer was struck simultaneously from each light at precisely .000000016678204759907602478778835723746 seconds after 12:00:00. That means the strikes occurred at A and B at exactly 12:00:00. It takes .00000001667792893852027063502108370407 seconds for light to travel from B on the train to the train observer at the midpoint. It takes .000000016678480590418212900804736688488 seconds for light to travel from A on the train to the midpoint observer on the train. So, the train observer had the light from B impact him .00000000000055165189794226578365298441767877 seconds before the light from A impacted him. Since the light from B impacted the train observer .00000001667792893852027063502108370407 seconds after 12:00:00 and it took light .00000001667792893852027063502108370407 seconds to travel from B to his midpoint position, the train observer concludes the strike occurred at B at exactly 12:00:00. Since the light from A impacted the train observer .000000016678480590418212900804736688488 seconds after 12:00:00 and it took light .000000016678480590418212900804736688488 seconds to travel from A to his midpoint position, the train observer concludes the strike occurred at A at exactly 12:00:00. So both observers acknowledge that the strikes occurred at exactly 12:00:00 at A and B. The embankment observer had both lights hit him simultaneously, and the train observer had the lights hit him at different times due to his 4,958 m/s velocity. Absolute simultaneity!!! Pete05-08-11, 08:57 PMYes, those numbers appear to be correct in a mathematical world with no time dilation and no length contraction, and under the assumption that the train observer has absolutely synchronized clocks. Are you ready to see my numbers now? Assumptions: The embankment is at rest Light travels at c with respect to the embankment Clocks on the embankment are synchronized with each other The train observer knows that light travels at c with respect to something at rest The train observer doesn't know that the embankment is at rest The train observer doesn't know that the embankment clocks are synchronized The train observer has precise clocks, but he doesn't know if they're synchronized Moving clocks run slowly by the Lorentz factor Moving rulers are shorter in the direction of motion by the Lorentz factor Are these premises acceptable to you? All my calculations must be perfectly consistent with these premises. From these premises, I believe I can prove that: Conclusions The train observer can't tell how fast he's going. His best measurements tell him he's at rest. His best measurements tell him that the speed of light is c with respect to the train. He can't synchronize his clocks. His best synchronization methods make his clocks out of sync with the embankment clocks The clocks he synchronized as well as he possibly could tell him that the lightning strike at the front of the train happened before the lightning strike at the back of the train. I'll go one step at a time, and wait for your questions and corrections before proceeding. In return, I expect that if I am able to do this to your satisfaction, then you will agree: that Einstein's world is a logically consistent world, and that if actual measurements in the real world match Einstein's world better than your own conceptual model, then your own conceptual model is wrong at relativistic speeds. Agreed? Motor Daddy05-08-11, 09:00 PMWhat is this time dilation and length contraction you speak of? Are you now going to change what you previously agreed to? Pete05-08-11, 09:04 PMWhat is this time dilation and length contraction you speak of? Are you now going to change what you previously agreed to? I'm not changing anything. What previous agreement do you mean? Motor Daddy05-08-11, 09:08 PMI'm not changing anything. What previous agreement do you mean? You just agreed to a world with no length contraction or time dilation. Now you are gonna give me different numbers? According to your assumptions, how much time does it take for light to travel 10 meters in the embankment frame? How much time does it take for light to travel 10 meters in the train frame? Pete05-08-11, 09:14 PMI agree that your numbers are correct in the world of no time dilation and no length contraction. But that's not Einstein's world. Remember the agreement: Here's a deal for you: We're considering two mathematical worlds: Newton's world and Einstein's world. You think that Newton's world is a better match for the real world than Einstein's. I think that Einstein's world is a better match. If you agree that only actual measurements of the real world (ie experiments) can decide who is right, then I'll show you the numbers in Einstein's world, one small step at a time, so you can point out any problems. Deal? How about this. We have a deal, but first you prove to me a relativity of simultaneity exists before you start using it in your method of calculations. Show me your numbers of Chapter 9 and prove to me that a relativity of simultaneity actually exists as Einstein claims it does. Prove it! Show me the numbers! We agree on the numbers in your mathematical world. Do you want to see the numbers in Einstein's mathematical world? RJBeery05-08-11, 09:15 PMPete, I'm following this discussion with interest; I'm curious to see if you succeed where I failed. Anyway, MD does not accept time or length contraction. Length is length is length, period. He believes that there exists a preferred frame of "true rest", and that light travels at c in absolute motion only from that frame. When I would bring up well established observations that contradict this way of thinking they would never seem to penetrate. Anyway, good luck! Motor Daddy05-08-11, 09:19 PMI agree that your numbers are correct in the world of no time dilation and no length contraction. But that's not Einstein's world. Remember the agreement: You haven't proven that a relativity of simultaneity exists, per the agreement. We agree on the numbers in your mathematical world. Do you want to see the numbers in Einstein's mathematical world? I want you to prove that a relativity of simultaneity exists before you start using the concept in your calculation. RJBeery05-08-11, 09:21 PMAs an addendum, MD isn't quite a "Newton's World" believer either, although I'm struggling to remember the subtle difference in his views. It interested me enough to tease out his ideas for falsifiability, but after having identified the problem I quickly lost interest. BTW, I do recall that in MD's world you can travel faster than light and observe events in reverse temporal order. This in itself isn't really proof of anything but it was one of the consequences that I pointed out. Pete05-08-11, 09:21 PMI want you to prove that a relativity of simultaneity exists before you start using the concept in your calculation. Correct, as per our agreement. I will not use the relativity of simultaneity in my calculations. You will notice that it is not listed in my assumptions. Are we agreed? AlexG05-08-11, 09:35 PMGood luck Pete. It ain't gonna happen, but go to it Don Quixote. Motor Daddy05-08-11, 09:51 PMCorrect, as per our agreement. I will not use the relativity of simultaneity in my calculations. You will notice that it is not listed in my assumptions. Are we agreed? Ok, so lay it out step by step for me, one at a time. Pete05-08-11, 10:21 PMFirst, the scenario. Point A and point B are marked 10 metres apart on the embankment. Point A' is moving, marked on the back of the train. Point B' is moving, marked on the front of the train. An observer M is standing on the embankment, halfway between point A and point B. An observer M' is standing on the train, halfway between point A' and point B'. The train passes the embankment at 4,958 m/s gamma = 1 / sqrt(1-v^2/c^2) = 1.0000000001367545054905367903816 At t=0.000: the front of the train is passing point B the back of the train is passing point A the train observer M' is passing embankment observer M M' has a clock with him that reads t'=0.000 A bolt of lightning strikes the front of the train and point B Another bolt of lightning strikes the back of the train and point A From this, I conclude that: the lightning bolts struck simultaneously the moving train is 10 actual metres long. metre rulers on the train are contracted to 1/gamma = 0.99999999986325 actual metres long clocks on the train are dilated, elapsing 1/gamma = 0.99999999986325 seconds every actual second OK so far? Motor Daddy05-09-11, 07:58 AMFirst, the scenario. Point A and point B are marked 10 metres apart on the embankment. Point A' is moving, marked on the front of the train. Point B' is moving, marked on the back of the train. An observer M is standing on the embankment, halfway between point A and point B. An observer M' is standing on the train, halfway between point A' and point B'. The train passes the embankment at 4,958 m/s gamma = 1 / sqrt(1-v^2/c^2) = 1.0000000001367545054905367903816 At t=0.000: the front of the train is passing point A the back of the train is passing point B the train observer M' is passing embankment observer M M' has a clock with him that reads t'=0.000 A bolt of lightning strikes the front of the train and point A Another bolt of lightning strikes the back of the train and point B From this, I conclude that: the lightning bolts struck simultaneously the moving train is 10 actual metres long. metre rulers on the train are contracted to 1/gamma = 0.99999999986325 actual metres long clocks on the train are dilated, elapsing 1/gamma = 0.99999999986325 seconds every actual second OK so far? Nope. Meter rulers on the train are not contracted, and clocks on the train are not dilated. 1. The meter rulers on the train are 1 meter in length, there is no contraction of rulers. A meter ruler is exactly 1 meter in length. If a stick is 0.99999999986325 meters long, it is not a meter stick, it is a 0.99999999986325 stick! 2. Clocks on the train are not dilated. A second is exactly one second, by definition. Both a meter and a second are standard definitions of distance and time, they don't change. You are baiting and switching by first saying the train is 10 meters long, and then saying it's actually 9.9999999986325 meters long. Which is it, is it 10 meters long or is it 9.9999999986325 meters long?? Also, one very important point: The front and back of the train are not passing the A and B points on the embankment, they are perfectly aligned with the embankment points, simultaneously. In order for the A and B points on the embankment to be 10 meters apart, and the train's front and back perfectly aligned simultaneously with the embankment's points, the train must be exactly 10 meters in length from front to back. If you say the train is actually 9.9999999986325 meters long, and the points on the embankment are 10 meters apart, there is no way the front and rear of the train can be aligned with the embankment points simultaneously. No way! AlexG05-09-11, 09:13 AMMeter rulers on the train are not contracted, and clocks on the train are not dilated. Repeated denial in the face of experimental evidence. Hopeless. Tach05-09-11, 09:20 AMNope. Meter rulers on the train are not contracted, and clocks on the train are not dilated. 1. The meter rulers on the train are 1 meter in length, there is no contraction of rulers. With respect to what frame? With respect to the car frame , no. With respect to any other frame moving wrt the car, yes. 2. Clocks on the train are not dilated. A second is exactly one second, by definition. With respect to what frame? With respect to the car frame , no. With respect to any other frame moving wrt the car, yes. Also, one very important point: The front and back of the train are not passing the A and B points on the embankment, they are perfectly aligned with the embankment points, simultaneously. In order for the A and B points on the embankment to be 10 meters apart, and the train's front and back perfectly aligned simultaneously with the embankment's points, the train must be exactly 10 meters in length from front to back. With respect to what frame? With respect to the car frame , yes. With respect to any other frame moving wrt the car, no. If points A and B are attached to the car, yes, otherwise, no. This is what happens when you don't know what you are talking about, MotorMouth. wellwisher05-09-11, 09:28 AMSimulataneity exists, however not all references are in a position to observe it when we use relative reference. To do so you need to include an energy balance. Special relativity has three equations, one for mass, one for distance and one for time. If you use only space-time ; distance-time, you can't determine absolute reference. Rather reference will appear relatice. You need to include relativistic mass, since energy conservation will not allow a stationary reference to pretend it gained energy, in the same way you can pretent it has motion using only distance and time. For example, I call this the relative reference work-out. You sit on the sidelines, stationary, and watch someone run. You then say reference is relative, and you are the one that is moving. This allows you to ignore energy conservation, and be the one burning all the calories, since you are the one in relative motion. On the other hand, if we are forced to do an energy balance by measuring calories, the relative reference trick won't work, because measuring the calories defines an absolute scale that tells us who is stationary and who is moving. Say we have someone stationary, and someone on a train is moving close to C. If we do an energy balance, you can tell one from the other, even if we decide to begin with relative reference, and define moving as stationary and the stationary as moving. Since only one reference has the energy needed to complete the energy balance, the question becomes, does the observed distance contraction and time dilation stem from the same mechanism for both, or from two different mechanisms due to an absolute reference based on energy? If we use the mass equation of special relativity, since only one reference has an actual mass increase, its visual effects are directly connected to its own absolute velocity. The other reference is not generating its own effect, since it lacks energy to make a real space-time impact. One reference is generating the effects for both references. This is an example of simulataneity since there is only one source for two effects. AlexG05-09-11, 09:52 AMSimulataneity exists, however not all references are in a position to observe it when we use relative reference. To do so you need to include an energy balance. Special relativity has three equations, one for mass, one for distance and one for time. If you use only space-time ; distance-time, you can't determine absolute reference. Rather reference will appear relatice. You need to include relativistic mass, since energy conservation will not allow a stationary reference to pretend it gained energy, in the same way you can pretent it has motion using only distance and time. For example, I call this the relative reference work-out. You sit on the sidelines, stationary, and watch someone run. You then say reference is relative, and you are the one that is moving. This allows you to ignore energy conservation, and be the one burning all the calories, since you are the one in relative motion. On the other hand, if we are forced to do an energy balance by measuring calories, the relative reference trick won't work, because measuring the calories defines an absolute scale that tells us who is stationary and who is moving. Say we have someone stationary, and someone on a train is moving close to C. If we do an energy balance, you can tell one from the other, even if we decide to begin with relative reference, and define moving as stationary and the stationary as moving. Since only one reference has the energy needed to complete the energy balance, the question becomes, does the observed distance contraction and time dilation stem from the same mechanism for both, or from two different mechanisms due to an absolute reference based on energy? If we use the mass equation of special relativity, since only one reference has an actual mass increase, its visual effects are directly connected to its own absolute velocity. The other reference is not generating its own effect, since it lacks energy to make a real space-time impact. One reference is generating the effects for both references. This is an example of simulataneity since there is only one source for two effects. Epic fail. There is NO absolute frame of reference. There is no absolute velocity. Reletavistic mass is a relative quntity, not an absolute. This is wrong on all levels. Motor Daddy05-09-11, 10:37 AMEpic fail. There is NO absolute frame of reference. There is no absolute velocity. Reletavistic mass is a relative quntity, not an absolute. This is wrong on all levels. ...and yet you insist that a frame can be at rest. At rest compared to what? At rest has to be relative to something. What is that something you refer to when you say "at rest?" Answer the question. Motor Daddy05-09-11, 10:40 AMPete, you have the same question to answer that you've continuously evaded. What do you mean when you say "at rest?" Describe your concept of "at rest." Me-Ki-Gal05-09-11, 10:55 AMBecause you're not the first person to come on here and claim to have demonstrated relativity is flawed using algebra on the level expected in a beginners SR textbook. Your problems and arguments are not new and previously have been retorted and explained away by people here and in the relativity research community as a whole. Depends your point of view. If you have only just come across relativity and all these weird experiments involving trains and flash lights and light cones then it might seem exciting and novel, even if you disagree with it. For those who have known relativity for years, if not decades, the said experiments and results are old news. More often than not a relativity nay-sayer is new to relativity and is still too entrenched in their Newtonian intuition and thinks that their comments and criticisms are novel or insightful or deep or advanced. Almost invariably they are none of those and the nay-sayer fails to realise just how little they have read and understood of relativity. If you aren't just a sock puppet of Jack_ then I suggest you look at threads he's started. He's the canonical example of what I've just said, someone with little or no knowledge, naive about his level of understanding (especially compared to professional researchers in relativity) and utterly unwilling to accept that perhaps he doesn't understand something he's only just read about. If you've made an honest attempt to learn some relativity and you're stuck on a few specific things then I'm sure people will be happy to help. If you're denouncing relativity because you haven't looked at it much and what you have looked at you've not bothered to think about then please don't let the door hit you on the way out. Alpha , Sorry to interrupt. If space time is curved could our universe be circling something else and our rate of constant in the motion is the boundary of light speed ? Except for the influence of massive objects does spacetime all curve the same direction our is it all willy nilly like my messy hair ? Me-Ki-Gal05-09-11, 11:02 AMPete, you have the same question to answer that you've continuously evaded. What do you mean when you say "at rest?" Describe your concept of "at rest." The constant of expansionism is probably as close to "Rest " in our life time . Speeding up from what I hear . If the universe is speeding up is it in a logarithmic fashion or at some steady constant ? Do we know how much the universe is speeding up in its expansion ? If it is is our frame of reference in flux? Does this influence the speed of light , but unknown to us for it always is the same from our vantage point ? wellwisher05-09-11, 11:38 AMTime and distance or space-time is relative. But relativistic mass is not relative, since it equates to energy via E=MC2. We can pretend to be moving relative to a moving reference. But once you do an energy balance, you can tell it is an illusion. For example, we have someone on a train looking outside. They think they are stationary and the landscape is moving. Someone at the station sees the train moving and themselves as stationary. Without an energy balance, it all seems relative. But if we add an mass/energy balance the person on the train sees the landscape moving. So we need to calculate the mass of those mountains times the velocity to get an idea of just how much energy there is in that motion. The other person at the station only see the mass of the train in motion. There is two different energy amounts that voids relative, since relative would mean both have the same energy. The magic trick doesn't work when we add mass/energy, which is why mass is downplayed so much. Some even try to explain mass in terms of space-time, so the magic trick is harder to see. This allows special effects that can make use of perpetual motion. origin05-09-11, 12:55 PM...and yet you insist that a frame can be at rest. At rest compared to what? At rest has to be relative to something. What is that something you refer to when you say "at rest?" Answer the question. You can say that one inertial frame is at rest relative to another inertial frame, but niether inertail frames are at rest in an absolute sense. Here is an example: Assume there is a space ship moving along at about 25 kph and another heading in the opposite direction also at 25 kph. The first ship can be viewed at rest compared to the second ship which is moving at 50 kph relative to the first ship. The second ship could also be viewed at rest relative to the first ship which is moving at 50 kph. A third ship may be sitting at some distance away at rest compared to those 2 ships and notice that they are both moving at 25 kpm towards each other. A fourth ship may be an even farther distance away at rest relative to the 3 ships and see that all 3 are moving together at 1000 kph. A 5th ship ...... This is hopeless you know, right? MD does not even understand the concept that the speed of light is constant. He thinks the speed of light is a constant like the speed of sound. He stated [from the trains reference]: If the train has a .5c velocity going down the tracks, and the train turns on a headlight that's located at the front of the train, 1 second later the light will be 149,896,229 meters in front of the train. The light traveled at c (299,792,458 m/s) for 1 second, and the train traveled at .5c (149,896,229 m/s) for 1 second, so the light is 149,896,229 meters in front of the train after 1 second. He thinks from the trains inertial frame that the speed of the light relative to the train is 149,896,229 m/s. He does not seem to grasp that the speed of light is constant, that is the speed of light relative to the train (or any other velocity frame) will be 299,792,458 m/s. I have asked him for evidence of this and he has ignored the request - which is not surprising as there is no evidence that this has any basis in fact. His belief also indicates that he has chosen to ignore all of the experimentation over the past 100 years showing that the inertial frame has no affect on the relative speed of light. Abandon all hope of reasoning with this guy. He is the epitome of willful ignorance. Motor Daddy05-09-11, 01:08 PMYou can say that one inertial frame is at rest relative to another inertial frame, but niether inertail frames are at rest in an absolute sense. Here is an example: Assume there is a space ship moving along at about 25 kph and another heading in the opposite direction also at 25 kph. The first ship can be viewed at rest compared to the second ship which is moving at 50 kph relative to the first ship. The second ship could also be viewed at rest relative to the first ship which is moving at 50 kph. A third ship may be sitting at some distance away at rest compared to those 2 ships and notice that they are both moving at 25 kpm towards each other. A fourth ship may be an even farther distance away at rest relative to the 3 ships and see that all 3 are moving together at 1000 kph. A 5th ship ...... You say there is a spaceship moving along at 25 kph. How did you determine the ship is traveling at 25 kph? Did you measure the distance it traveled in a specific amount of time? How exactly did you measure the distance, and what are the points you measured from? Certainly you did not measure from the other ship, , as the distance was closing at the rate of 50 kph. So exactly how did you determine the ship was moving at 25 kph? You don't even understand where you go wrong. You just make up numbers, and then change the numbers in order to fit Einstein's delusional world. Do you understand that in order for you to have measured the velocity of an object that the time must have already elapsed, and that you are looking at a record of the past? The stop watch has already stopped, the test is completed. Why can't you comprehend that?? ...and you told me to assume the ship is moving along at 25 kph. Then you want me to assume that the ship can be considered at rest (with respect to what I don't know). Are you now telling me to disregard the first assumption that the ship is moving along at 25 kph, and to assume the ship has a zero velocity? Make up my mind, will you? Which is it? By the way, even a zero velocity has to have been measured. How did you measure the zero velocity, and how much time did you perform the test, or has the ship always been at a zero velocity? Did it appear out of nowhere instantaneously, or did it come from some other place a distance away? If so, should I disregard that motion in my calculations of distance and time? You're clueless! AlexG05-09-11, 01:43 PMBut relativistic mass is not relative, since it equates to energy via E=MC2. Wrong. Relativistic mass is relative, since it depends on RELATIVE VELOCITIES. There is NO absolute frame of reference. There is also no arguing with those who believe there is. Motor Daddy, "AT REST" with respect to the arbitrarily chosen inertial frame of the observer. Motor Daddy05-09-11, 01:49 PMMotor Daddy, "AT REST" with respect to the arbitrarily chosen inertial frame of the observer. So basically you just make it up out of thin air? You don't perform any measurements of any kind? So you can just as easily say you have a 29.345 m/s velocity as you can a zero velocity? You say at rest and don't even realize that is a velocity, a zero velocity, which needs to be substantiated by facts, and yet..you can't do that, because you made it up out of thin air! We are both in the same ship. You say the ship has a 0 m/s velocity, I say the ship has a 325.56743 m/s velocity. origin05-09-11, 01:49 PMYou say there is a spaceship moving along at 25 kph. How did you determine the ship is traveling at 25 kph? Did you measure the distance it traveled in a specific amount of time? How exactly did you measure the distance, and what are the points you measured from? Certainly you did not measure from the other ship, , as the distance was closing at the rate of 50 kph. So exactly how did you determine the ship was moving at 25 kph? You don't even understand where you go wrong. You just make up numbers, and then change the numbers in order to fit Einstein's delusional world. Do you understand that in order for you to have measured the velocity of an object that the time must have already elapsed, and that you are looking at a record of the past? The stop watch has already stopped, the test is completed. Why can't you comprehend that?? ...and you told me to assume the ship is moving along at 25 kph. Then you want me to assume that the ship can be considered at rest (with respect to what I don't know). Are you now telling me to disregard the first assumption that the ship is moving along at 25 kph, and to assume the ship has a zero velocity? Make up my mind, will you? Which is it? By the way, even a zero velocity has to have been measured. How did you measure the zero velocity, and how much time did you perform the test, or has the ship always been at a zero velocity? Did it appear out of nowhere instantaneously, or did it come from some other place a distance away? If so, should I disregard that motion in my calculations of distance and time? You're clueless! Why are you are making such a supreme effort to not understand? I don't know why you want to live in willful ignorance - how odd.:shrug: Motor Daddy05-09-11, 01:56 PMWhy are you are making such a supreme effort to not understand? I don't know why you want to live in willful ignorance - how odd.:shrug: Why do you tell me to assume the ship has a 25 kph velocity, and then change your story and tell me the ship has a 0 kph velocity?? :shrug: How did you determine the 25 kph velocity?? Magneto_105-09-11, 02:29 PMWhat do you mean when you say "at rest?" Describe your concept of "at rest." Motor Daddy, Let me take a swing at this, if I may?:) The concept of the "inertial frame of reference" and "rest" are a bit confusing to the "Relativist." This is why I was forced to to add an addendum to Newton's First Law of Motion in the form of an Aphorism: Super Principle of Motion #1. I will make the following quote from the book: Super Principia Mathematica - The Rage to Master Conceptual & Mathematical Physics: The First Law of Motion (http://www.superprincipia.com/First_Law_Of_Motion.htm); by Robert Louis Kemp All uniform motion and velocities are determined to be relative, and are the measure of the time rate of change in the position of a body, relative to some frame of reference. The specific external uniform translational velocity of a system mass body in motion is the displacement of the Center of Mass of that body, over equal distances, in a particular direction over equal amounts of time, relative to an external inertial frame of reference and the center of mass of the system body. There is no way to measure the absolute translational velocity of a system body in motion in the universe. The velocity of a body can only be measured relative to its own-ship Center of Mass/Momentum frame or to other external frames of reference in the universe. The velocity of a body is therefore a relative effect, and is typically measured relative to the earth. However, the earth itself is not at rest, it is rotating on its axis, and revolving around the sun. The sun itself is moving relative to the center of our Milky Way galaxy; and our galaxy is moving relative to other galaxies. All velocities must be measured relative to some other specified coordinate system. Law 1.1: First Law of Motion — Relative to an Inertial frame of reference, a body preserves a state of uniform momentum, kinetic energy, squared velocity, and velocity, in a straight line equal distances in equal times, unless it is compelled to change its state of uniform motion by an unbalanced external or internal force acting on the body. http://www.superprincipia.com/internet_images/Principle_of_Motion_1.gif Aphorism 1.1: Super Principle of Motion #1 - There is always motion of one body relative to any other body at rest in the universe; and the relative motion of any one body can never be reduced to zero. Therefore there is no frame of reference that can be measured that is truly at rest; thus, being at rest is just as natural as being in a state of uniform motion; rest is therefore a special state of motion. Best AlphaNumeric05-09-11, 02:40 PMI will make the following quote from the book: Super Principia Mathematica - The Rage to Master Conceptual & Mathematical Physics: The First Law of Motion (http://www.superprincipia.com/First_Law_Of_Motion.htm); by Robert Louis Kemp Referring to yourself in the third person, to a book you wrote, as a means of trying to legitimise your claims is dishonest, both in terms of providing 'scientific' references (which your work is not even close to) and in terms of trying to hide self promotion. If you can't provide reputable sources don't pretend you have any. Don't pretend you aren't Robert Kemp when you've repeatedly said you are him. Don't promote a book you authored which is vanity published and hasn't passed (and couldn't) scientific review. There are anti-promotion rules on this forum and referring to yourself in the third person doesn't mean you can ignore them. Motor Daddy05-09-11, 02:47 PMMotor Daddy, Let me take a swing at this, if I may?:) There is no way to measure the absolute translational velocity of a system body in motion in the universe. The velocity of a body can only be measured relative to its own-ship Center of Mass/Momentum frame or to other external frames of reference in the universe. Strike 1! :) Yes there is, and I've already shown how multiple times on this board. I did it in this thread too. Since the meter is basically defined as a specific light travel time, distance is simply light travel time. Light travels in space at a specific speed. So it is possible to measure the velocity of a box in space from inside the box, or a train's velocity in space from inside the train, by measuring the amount of time it takes light to travel. Since light always travels at the same speed, it is possible to know one's own motion from "inside the box" by simply measuring the amount of time it takes light to travel a specific distance in the box. I've done this in this thread as to showing the absolute velocity of the embankment, and also the absolute velocity of the train. Neither velocity are derived from the other. wellwisher05-09-11, 02:57 PMWrong. Relativistic mass is relative, since it depends on RELATIVE VELOCITIES. Let me give an example. In a particle accelerator, some particles are given velocity close to C, while most of the matter in the lab will remain stationary. This velocity can't as easily be defined as relative,since there will be energy differences we can measure, if you look closer. We can tell the difference between the relative references by the magnetic field strengths, since this will increase with absolute velocity, but it it won't increase with relative velocity. The lab will not start to generate magnetic fields simply by assuming all is relative and the lab is in motion when it is not. That would be a magic trick, since charge will need actual motion. Only where there is real energy and absolute velocity, will there be real effects. The rest is pretend that needs magic to fool the audience. I see relativistic mass as the mass version of the magnetic induction caused by charge velocity. It creates fields which store energy. We can't magically make a strong magnetic field appear in our reference by assuming relative motion. It needs absolute motion. Pete05-09-11, 03:07 PMNope. Meter rulers on the train are not contracted, and clocks on the train are not dilated. 1. The meter rulers on the train are 1 meter in length, there is no contraction of rulers. A meter ruler is exactly 1 meter in length. If a stick is 0.99999999986325 meters long, it is not a meter stick, it is a 0.99999999986325 stick! 2. Clocks on the train are not dilated. A second is exactly one second, by definition. I'm giving you the numbers in the mathematical world of time dilation and length contraction, Motor Daddy, just as we agreed. A bunch of standard metre rulers and standard clocks are on the train, but because the train is moving they are no longer accurate. The metre rulers are short. The clocks tick slowly. Would it help if I say "train ruler" instead of "metre ruler"? A train ruler is 9.9999999986325 metres long. Both a meter and a second are standard definitions of distance and time, they don't change. You are baiting and switching by first saying the train is 10 meters long, and then saying it's actually 9.9999999986325 meters long. Which is it, is it 10 meters long or is it 9.9999999986325 meters long?? The train is 10 metres long. Also, one very important point: The front and back of the train are not passing the A and B points on the embankment, they are perfectly aligned with the embankment points, simultaneously. In order for the A and B points on the embankment to be 10 meters apart, and the train's front and back perfectly aligned simultaneously with the embankment's points, the train must be exactly 10 meters in length from front to back. Yes, that's what I said in the conclusion to that post. If you say the train is actually 9.9999999986325 meters long I don't. The train is 10 actual metres long. Rulers on the train are contracted to 0.99999999986325 m. There are 10.000000001367545 train rulers in 10 actual metres. The train observer measures the train to be 10.000000001367545 rulers long. Magneto_105-09-11, 03:09 PMSo it is possible to measure the velocity of a box in space from inside the box, or a train's velocity in space from inside the train, by measuring the amount of time it takes light to travel. Since light always travels at the same speed, it is possible to know one's own motion from "inside the box" by simply measuring the amount of time it takes light to travel a specific distance in the box. Motor Daddy, Free from any gravitational field and the box moving at relativistic speed will conclude that what you have written above about the "Box Inertial Frame" and "light" are true. However, an external observer outside of the box and making measurements of the "light pulse" and the very high speed moving "Box Inertial Frame", will conclude that: time, distance, wavelength, and frequency are all different for the "Proper" Center of Mass, moving "Box Inertial Frame." Best Motor Daddy05-09-11, 03:13 PMI'm giving you the numbers in the mathematical world of time dilation and length contraction, Motor Daddy, just as we agreed. A bunch of standard metre rulers and standard clocks are on the train, but because the train is moving they are no longer accurate. You mean you are on the train and acknowledge the "train is moving?" What is it moving compared to, and at what rate, and how did you measure that rate on the train? Motor Daddy05-09-11, 03:22 PMThe train is 10 actual metres long. Rulers on the train are contracted to 0.99999999986325 m. There are 10.000000001367545 train rulers in 10 actual metres. The train observer measures the train to be 10.000000001367545 rulers long. So the meter sticks on the train are not actually one meter in length? In other words, how much time does it take for light to travel the length of one of those train sticks (which are not a true meter) when it is on the train parallel to the tracks? Pete05-09-11, 03:23 PMYou mean you are on the train and acknowledge the "train is moving?" What is it moving compared to, and at what rate, and how did you measure that rate on the train? No, I'm not on the train. Yes, I'm working with the assumption that the embankment is at absolute rest, and that the train is moving at 4958 m/s. The train observer does not yet know if the train is moving. Motor Daddy05-09-11, 03:27 PMNo, I'm not on the train. Yes, I'm working with the assumption that the embankment is at absolute rest, and that the train is moving at 4958 m/s. The train observer does not yet know if the train is moving. How much time would it take light to travel the length of one of those train sticks when it is on the train? Pete05-09-11, 03:32 PMFrom front to back, it takes t=d/(c+v) = 3.335585787248 ns From back to front, it takes t=d/(c-v) = 3.335696117627 ns origin05-09-11, 03:32 PMWhy do you tell me to assume the ship has a 25 kph velocity, and then change your story and tell me the ship has a 0 kph velocity?? :shrug: Golly, if that has blown your mind then this is really even more fruitless than I first thought. If willful ignorance is bliss - you certainly have reached nirvana. Motor Daddy05-09-11, 03:41 PMFrom front to back, it takes t=d/(c+v) = 3.335585787248 ns From back to front, it takes t=d/(c-v) = 3.335696117627 ns So the light travel time one way is different than the light travel time the other way, when measured on the train? Motor Daddy05-09-11, 03:55 PMGolly, if that has blown your mind then this is really even more fruitless than I first thought. If willful ignorance is bliss - you certainly have reached nirvana. Thanks for the reply, it speaks volumes of your inability to prove me wrong, and your inability to explain yourself. Motor Daddy05-09-11, 04:11 PMLadies and Gentlemen, Pete has left the building. :) Emil05-09-11, 04:24 PM@Motor Daddy, What I will say is for general and not necessarily for the present example. I agree with reporting speed at speed light. But be prudent because this speed is not completely determined because the orientation is undetermined. So if the object1 has a speed V1 and the object2 has a speed V2, that does not mean relative speed between these two objects is V = V1-V2. This addition or subtraction is made vectorial, taking into account the orientation of the two velocity vectors. They make the same mistake, because if the observer is not on the train and not on the tracks, the relative speed between him and the train is made through a vector decomposition. So when the train runs right in front of the observer, the relative speed between them is 0. Pete05-09-11, 05:10 PMLadies and Gentlemen, Pete has left the building. :) I have a life, MD. I'm assuming you do too? I made the previous couple of posts over breakfast. Posting over the next 8 hours will be sporadic between classes. So the light travel time one way is different than the light travel time the other way, when measured on the train? Those are the actual travel times. Measuring on the train is trickier, because the train clocks are dilated, and haven't been synchronized yet. That's the next step, if you're happy with the facts so far. Motor Daddy05-09-11, 05:17 PMThose are the actual travel times. Measuring on the train is trickier, because the train clocks are dilated, and haven't been synchronized yet. That's the next step, if you're happy with the facts so far. What do you mean by "the actual travel times?" Do you plan to use a different sync method from the one you (indirectly) agreed to using for the embankment? The clocks on the embankment are absolutely sync'd. In other words, at any point in time they read as one. Another way to put it is that when I am at one clock and it says 12:00:00, I know for a fact the other clock reads 12:00:00, like I know the time in NY is the same time in Florida at any point in time. One time zone. arfa brane05-09-11, 06:10 PMMotor Daddy: there are two frames of reference: the embankment, and the train. Is it really that difficult to understand? Pete said The train observer measures the train to be 10.000000001367545 rulers long. Where the train observer is on the embankment, and "at rest". So the observer, who is not on the train, sees different lengths than an observer who is on the train and moving with it. Yeesh. Tach05-09-11, 06:21 PMSo the light travel time one way is different than the light travel time the other way, when measured on the train? Not on the train, in the embankment frame. How dense are you? Motor Daddy05-09-11, 06:25 PMMotor Daddy: there are two frames of reference: the embankment, and the train. Is it really that difficult to understand? Pete said Where the train observer is on the embankment, and "at rest". So the observer, who is not on the train, sees different lengths than an observer who is on the train and moving with it. Yeesh. It simply boils down to the fact that the train observer and the embankment observer both agree that the strikes occurred at A and B simultaneously. I say the strikes occurred at A and B simultaneously and that both observers agree, and Pete (and Einstein) says the observers don't agree with each other as to when the strikes occurred at A and B. I showed mathematically that the strikes occurred at exactly 12:00:00 at A and B, and that both observers agree with that. Pete says I'm full of it and he can prove it. I'm all ears!! First we have to settle on the details, and so far, there is a thorn in Pete's side, and that is that he has acknowledged that it takes light a different amount of time to travel the length of the train, depending on which direction you measure it. Exactly my point, and how I am able to calculate the absolute velocity from within. We'll see....... Motor Daddy05-09-11, 06:38 PMNot on the train, in the embankment frame. How dense are you? The stick is on the train, and these are times he gave me. From front to back, it takes t=d/(c+v) = 3.335585787248 ns From back to front, it takes t=d/(c-v) = 3.335696117627 ns Are you speaking for Pete now and going to give me different times from both the train and the embankment of how much time it takes for light to travel the length of the stick when it is on the train? The actual distance and times are irrelevant, the point is that it takes a different amount of time for light to travel the length of the stick, depending on which way you measure it, as light has to travel further in one direction than the other. Prove it doesn't! Tach05-09-11, 07:20 PMThe stick is on the train, and these are times he gave me. You are totally dense. No chance of ever getting well. the point is that it takes a different amount of time for light to travel the length of the stick, depending on which way you measure it, as light has to travel further in one direction than the other. Prove it doesn't! That was precisely the point Pete made to you and you just denied it because you didn't understand it (http://www.sciforums.com/showpost.php?p=2750340&postcount=202). Motor Daddy05-09-11, 07:25 PMYou are totally dense. No chance of ever getting well. That's what I though. You are among the camp that says that it takes the same time for light to travel from a lamp post to a person at 10 meters, a person at 15 meters, and a person at 20 meters. Point being, If I am a distance away from a lamp post and measure the amount of time it takes for light to reach me, you say it takes the same amount of time for the light to reach me if I start running away from the lamp as soon as the light departs the lamp. You're clueless! ...and to put icing on the cake, you say the time is the same if I start running towards the lamp when the light is emitted. Tach05-09-11, 07:29 PMThat's what I though. You are among the camp that says that it takes the same time for light to travel from a lamp post to a person at 10 meters, a person at 15 meters, and a person at 20 meters. Not at all. I am in the camp that has determined that you are totally dense and that you can't follow the simplest proofs because you can only engage mouth and not brain. arfa brane05-09-11, 07:52 PMThe stick is on the train, and these are times he gave me. The stick is on the train, the observer is not on the train but standing on the "stationary" embankment. Oh, and the stick is not an observer, just in case that needed clarification. Motor Daddy05-09-11, 07:55 PMThe stick is on the train, the observer is not on the train but standing on the "stationary" embankment. Oh, and the stick is not an observer, just in case that needed clarification. Just to clarify, each end of the stick IS an observer, with a clock! Tach05-09-11, 07:57 PMJust to clarify, each end of the stick IS an observer, with a clock! Yep, you have the brain of a stick. Pete05-09-11, 08:04 PMPete said Where the train observer is on the embankment, and "at rest". So the observer, who is not on the train, sees different lengths than an observer who is on the train and moving with it. No. The train observer is riding on the train. Not at all. I am in the camp that has determined that you are totally dense and that you can't follow the simplest proofs because you can only engage mouth and not brain. Tach, you're not helping. Guys, please let me work through this exercise with MD without interjections. Thanks. Pete05-09-11, 08:06 PMWhat do you mean by "the actual travel times?" The time measured using clocks we know are synchronized and not dilated, ie the embankment clocks. Do you plan to use a different sync method from the one you (indirectly) agreed to using for the embankment? Not unless you want to. We'll get to synchronizing train clocks shortly. One step at a time, right? The clocks on the embankment are absolutely sync'd. Yes, that's the assumption I'm working with. Motor Daddy05-09-11, 08:39 PMWe'll duke it out in a moment when it comes to the train clocks, but you may proceed, I'm good with the embankment. arfa brane05-09-11, 08:53 PMNo. The train observer is riding on the train. Oops, my bad. However, since there are clocks on the embankment which are synchronous, the observer on the train is able to postulate a "virtual" observer on the embankment, i.e. the clocks. This is because the observer on the train can see the same clocks, and mentally "transform" their location to the stationary embankment. Hope I'm not confused about that. Pete05-09-11, 08:54 PMRecap - the story so far: Assumptions: The embankment is at rest Light travels at c with respect to the embankment Clocks on the embankment are synchronized with each other The train observer knows that light travels at c with respect to something at rest The train observer doesn't know that the embankment is at rest The train observer doesn't know that the embankment clocks are synchronized The train observer has precise clocks, but he doesn't know if they're synchronized Moving clocks run slowly by the Lorentz factor Moving rulers are shorter in the direction of motion by the Lorentz factor The scenario Point A and point B are marked 10 metres apart on the embankment. Point A' is moving, marked on the back of the train. Point B' is moving, marked on the front of the train. An observer M is standing on the embankment, halfway between point A and point B. An observer M' is standing on the train, halfway between point A' and point B'. The train passes the embankment at 4,958 m/s gamma = 1 / sqrt(1-v^2/c^2) = 1.0000000001367545054905367903816 At t=0.000: the front of the train is passing point B the back of the train is passing point A the train observer M' is passing embankment observer M M' has a clock with him that reads t'=0.000 A bolt of lightning strikes the front of the train and point B Another bolt of lightning strikes the back of the train and point A From this, I conclude that: the lightning bolts struck simultaneously the moving train is 10 actual metres long. rulers on the train are contracted to 1/gamma = 0.99999999986325 actual metres long The train observer measures the train to be 10.000000001367545 rulers long clocks on the train are dilated, elapsing 1/gamma = 0.99999999986325 seconds every actual second It takes light t=d/(c+v) = 3.335585787248 ns to go from the front of a train ruler to the back of a train ruler It takes light t=d/(c-v) = 3.335696117627 ns to go from the back of a train ruler to the front of a train ruler Now, the next step... At t = d/(c+v) = 16.67792893852027 ns : The flash from lightning bolt B reaches M' (the train observer) The clock at M' reads t' = t/gamma = 16.67792893623949 ns At t = d/c = 16.67820475990760 ns: The flash from both lightning bolts reaches M At t = d/(c-v) = 16.67848059041821 ns: The flash from lightning bolt A reaches M' The clock at M' reads t' = t/gamma = 16.67848058813736 ns What can the train observer conclude from the readings on his clock? Only that his clock elapsed 0.55 picoseconds between the front lightning flash reaching him and the rear flash reaching him. But since doesn't know how fast he's going in what direction, and there are no clocks anywhere else on the train that are synchronized with the centre clock, he can't tell from that data alone which flash occurred first. Questions or problems? So how will we proceed? Sync clocks first, or measure velocity without synced clocks? We could have M' measure his velocity using a single clock, a light flash, and a mirror We could have M' measure his velocity using unsynchronized clocks (flash one way, flash the other way) We could have M' synchronize the clocks at each end of the train with each other in some way. Perhaps we could send identical robots from the centre to each end, starting in the middle at the same Which way would you prefer? Shall we try all of them? Other suggestions are welcome. Pete05-09-11, 08:58 PMOops, my bad. However, since there are clocks on the embankment which are synchronous, the observer on the train is able to postulate a "virtual" observer on the embankment, i.e. the clocks. This is because the observer on the train can see the same clocks, and mentally "transform" their location to the stationary embankment. Hope I'm not confused about that. In this scenario, we're not (yet) allowing the train observer to see the embankment clocks. All the train observer has is his contracted rulers, his dilated clock/s, and the flashes of lightning. Motor Daddy05-09-11, 09:21 PMThe light travel times are correct, the clock readings on the train are incorrect. You have not established that the clocks on the train tick any faster or slower than the embankment's clocks. Faster or slower than what? As far as the train observer is concerned, his clocks are the ONLY clocks in the universe. He has no windows to the outside world. I agree with your light travel times, they are exactly the same as my travel times in my example. The embankment observer had both lights hit him simultaneously. The embankment is at a zero velocity. Light traveled equal distance to reach the embankment observer. What time was it on the embankment observer's watch when the lights hit him? Motor Daddy05-09-11, 09:48 PMAlso, just to stay in sync with Einstein's Chapter 9, A is at the rear of the train and B is at the front of the train, so you have the times reversed in your post. I'm sure that's what you meant, it's just a small technicality. Motor Daddy05-09-11, 09:57 PM...and just a side note: You've just proven that in the train frame, it takes more time for light to travel from A to the observer at the midpoint than it does for light to travel from B to the observer at the midpoint. In the train frame, those are equal distances, and yet light takes different amounts of time to travel that same distance. That is a fact, so you have some explaining to do. Pete05-09-11, 11:01 PMThe light travel times are correct, the clock readings on the train are incorrect. You have not established that the clocks on the train tick any faster or slower than the embankment's clocks. Faster or slower than what? As far as the train observer is concerned, his clocks are the ONLY clocks in the universe. He has no windows to the outside world. The train observer doesn't yet know if his clocks are dilated or by how much, but we do. We've established that the embankment is at rest. We've established that the train is moving at 4958m/s. We've established that in the mathematical world we're working in, moving clocks run slowly. So we conclude the train clocks are dilated, elapsing one tick every 1.0000000001367545 seconds. What time was it on the embankment observer's watch when the lights hit him? The flashes reached him at t=16.67820475990760 ns, so that's what the embankment clock (which we've said are at rest, undilated, and absolutely sync'd) at M reads. Also, just to stay in sync with Einstein's Chapter 9, A is at the rear of the train and B is at the front of the train, so you have the times reversed in your post. I'm sure that's what you meant, it's just a small technicality. I'll edit the previous posts to match that convention. ...and just a side note: You've just proven that in the train frame, it takes more time for light to travel from A to the observer at the midpoint than it does for light to travel from B to the observer at the midpoint. In the train frame, those are equal distances, and yet light takes different amounts of time to travel that same distance. That is a fact, so you have some explaining to do. No, the light travel times haven't yet been measured by the train observer. All he knows is what his clock read when each flash reached him. He doesn't know when the lightning actually struck, because he doesn't have synchronized clocks at the ends of the train. We know that they struck simultaneously, but the train observer doesn't. Are you ready for the train observer to synchronize his clocks, or to measure his velocity? James R05-10-11, 12:21 AMMotor Daddy: For completeness, I will respond to your post about Einstein's thought experiment. Let's look at Einstein's train thought experiment in Chapter 9. The Relativity of Simultaneity. Einstein, Albert. 1920. Relativity: The Special and General Theory. Einstein conveniently forgot to put numbers to the thought experiment, so let's do it for him, shall we? He didn't forget. Real physicists work with algebra, calculus and other mathematical tools, not just arithmetic. They do that because doing it that way means that you solve more than one problem at a time. Moreover, you can look at your solutions and see which factors were important and which cancelled out during the analysis. Finally, you avoid all the messy streams of numbers, like the ones you've been posting. More on that in moment. The observer on the train measures the time it takes light to go from the rear of the train car to the front of the train car, which is 11.9915 meters in length in the train frame. Light takes .00000004 seconds to travel the length of the train. That means the absolute velocity of the train is 4,958 m/s. Why choose a train that is 11.9915 metres long? Why not make it 12 metres, or 10 metres? 11.9915 is just an arbitrary mess. Or did you choose that number because you took the speed of light to be exactly 299792458 metres per second, and you wanted the travel time to be exactly 0.00000004 seconds? The number 299792458 is not important in analysing this situation, you know. You can use 300000000 and the general conclusions will be the same. If time dilation and length contraction do not exist, then approximating the speed of light by 300,000,000 m/s won't affect that conclusion. For ease of calculation, you may as well use nice round numbers. If you did use c=300,000,000 m/s, then in 0.00000004 seconds light would travel exactly 12 metres. Your first error also appears here: measuring the travel time of light on the train tells you nothing about the speed of the train relative to the embankment. The observer on the tracks measures the time it takes light to travel the distance between two clocks on the track, which is 1 meter. It takes light .0000000033356409519815204957557671447492 seconds to travel the distance, which means the track has an absolute zero velocity. Again, measuring the light travel time on the track tells you nothing about the absolute speed of the track. It is 10 meters from A to B on the train in the train frame, and 10 meters from A to B on the embankment in the embankment frame. That's wrong, because in actual fact the embankment sees the train as length contracted, and vice versa. So, at least one of your figures must be wrong. Both observers are at the midpoint between A and B in their respective frames. Lightening strikes A and B as the two points on the train coincide with the two points on the embankment. Coincide in space, or in time, or both? Spatially separated events that are simultaneous in one frame cannot be simultaneous in any other frame. Light takes .000000016678204759907602478778835723746 seconds for each light from A and B to strike the embankment observer. Ok. Then you're implying that the events at A and B occurred simultaneously in the embankment frame. That means they were not simultaneous in the train frame. It takes .00000001667792893852027063502108370407 seconds for light to travel from B on the train to the train observer at the midpoint. It takes .000000016678480590418212900804736688488 seconds for light to travel from A on the train to the midpoint observer on the train. Are those times measured in the embankment frame or the train frame? If they are supposed to be in the train frame, then they can't be different and you're wrong. I assume, therefore, that you're measuring the times in the embankment frame. So, the train observer had the light from B impact him .00000000000055165189794226578365298441767877 seconds before the light from A impacted him. Makes sense, since the train observer is moving towards the location of the strike at B and away from A. Since the light from B impacted the train observer .00000001667792893852027063502108370407 seconds after 12:00:00 and it took light .00000001667792893852027063502108370407 seconds to travel from B to his midpoint position, the train observer concludes the strike occurred at B at exactly 12:00:00. Since the light from A impacted the train observer .000000016678480590418212900804736688488 seconds after 12:00:00 and it took light .000000016678480590418212900804736688488 seconds to travel from A to his midpoint position, the train observer concludes the strike occurred at A at exactly 12:00:00. But you've measured the times in the embankment frame, then simply assuming that the times measured in the train's frame are the same. That's just wrong, and it's an assumption you have not established is valid at all. So both observers acknowledge that the strikes occurred at exactly 12:00:00 at A and B. No. Your mistake is that you've only used the embankment clocks here, and ignored the possibility that the train clocks say something different. Absolute simultaneity!!! Absolute, mistake-ridden rubbish. James R05-10-11, 12:51 AMMotor Daddy: You may wish to look at a detailed derivation of special relativistic time dilation and length contraction that I wrote back in 2004. Since you don't understand the basics at this stage, this may be a quick way of getting up to speed just a little. You only need to read one post. Special Relativitistic time dilation and length contraction derived Neddy Bate05-10-11, 01:28 AMLet's look at Einstein's train thought experiment in Chapter 9. The Relativity of Simultaneity. Einstein, Albert. 1920. Relativity: The Special and General Theory. It simply boils down to the fact that the train observer and the embankment observer both agree that the strikes occurred at A and B simultaneously. The embankment observer says that the strikes were simultaneous, because they reached her simultaneously, from equal distances away. The train based observer says that the strikes were not simultaneous, because they did not reach her simultaneously, from equal distances away. That is all. :D Pete05-10-11, 05:33 AMThe embankment observer says that the strikes were simultaneous, because they reached her simultaneously, from equal distances away. The train based observer says that the strikes were not simultaneous, because they did not reach her simultaneously, from equal distances away. That is all. :D Hi Neddy, That also relies on light approaching the train observer at equal rates from each end of the train, which isn't one of the premises in the particular approach I'm taking in this exercise. Motor Daddy05-10-11, 07:13 AMJames. I am arguing Einstein is wrong, why would I use his methods, or postulates? You seem to think that I have to use his methods and work under his postulates to prove him wrong. That's absurd. Motor Daddy05-10-11, 07:29 AMThe train observer doesn't yet know if his clocks are dilated or by how much, but we do. No we don't know that. Where did you prove that? That stems from using Einstein's methods, not mine. We've established that in the mathematical world we're working in, moving clocks run slowly. So we conclude the train clocks are dilated, elapsing one tick every 1.0000000001367545 seconds. We have NOT established that. Show me where we established that, other than you starting with that assumption, which I disagreed with at the beginning. Pete05-10-11, 07:31 AMRemember the agreement: Here's a deal for you: We're considering two mathematical worlds: Newton's world and Einstein's world. You think that Newton's world is a better match for the real world than Einstein's. I think that Einstein's world is a better match. If you agree that only actual measurements of the real world (ie experiments) can decide who is right, then I'll show you the numbers in Einstein's world, one small step at a time, so you can point out any problems. Deal? How about this. We have a deal, but first you prove to me a relativity of simultaneity exists before you start using it in your method of calculations. Show me your numbers of Chapter 9 and prove to me that a relativity of simultaneity actually exists as Einstein claims it does. Prove it! Show me the numbers! Do you want to see the numbers in Einstein's mathematical world, or not? Motor Daddy05-10-11, 07:36 AMRemember the agreement: Do you want to see the numbers in Einstein's mathematical world, or not? We are going step by step, hashing out our differences as they appear. You can't just start with the premise that clocks magically run slower or faster, and that rulers expand and contract, just like I can't say the train observer knows both strikes occurred simultaneously because we've established that as a fact on the embankment. You've shown nothing to back up your assertion that clocks run differently on the train, or that rulers are contracted on the train. The train is a separate issue, of which the observer on the train knows only what he knows in his own little world. Motor Daddy05-10-11, 07:46 AMIf you agree that only actual measurements of the real world (ie experiments) can decide who is right, then I'll show you the numbers in Einstein's world, one small step at a time, so you can point out any problems. Where are your actual measurements on the train that says the clocks run slower, and the rulers are contracted, just knowing what you know on the train? That's the deal, remember? Pete05-10-11, 08:02 AMWe are going step by step, hashing out our differences as they appear. You can't just start with the premise that clocks magically run slower or faster, and that rulers expand and contract, just like I can't say the train observer knows both strikes occurred simultaneously because we've established that as a fact on the embankment. :shrug: That's the agreement we made. I said I'd show you the numbers in the world of length contraction and time dilation. You said we had a deal. Motor Daddy05-10-11, 08:03 AM:shrug: That's the agreement we made. I said I'd show you the numbers in the world of length contraction and time dilation. You said we had a deal. I quote the deal again: If you agree that only actual measurements of the real world (ie experiments) can decide who is right, then I'll show you the numbers in Einstein's world, one small step at a time, so you can point out any problems. Pete05-10-11, 08:17 AMYou've quoted post 129 of this thread. That post very clearly states that I would be working show tin the mathematical world of time dilation and length contraction. And as you quoted, I said I'd show you the numbers in Einstein's mathematical world. In return, you would agree that only actual measurements of the real world (ie experiments) can decide who is right. We're not doing actual measurements in the real world here, MD. I'm not actually looking at a train going past an embankment at 4958m/s. I'm just typing on a keyboard and putting words on a screen. We're working out the numbers in Einstein's mathematical world. You asked for the numbers, over and over again. Now you're getting them. The topic of this thread was brought up in another (Light at Light speed), and I'm bringing it back here to avoid a major sidetrack in that thread. Here's a deal for you: We're considering two mathematical worlds: Newton's world and Einstein's world. You think that Newton's world is a better match for the real world than Einstein's. I think that Einstein's world is a better match. If you agree that only actual measurements of the real world (ie experiments) can decide who is right, then I'll show you the numbers in Einstein's world, one small step at a time, so you can point out any problems. Deal? How about this. We have a deal, but first you prove to me a relativity of simultaneity exists before you start using it in your method of calculations. Show me your numbers of Chapter 9 and prove to me that a relativity of simultaneity actually exists as Einstein claims it does. Prove it! Show me the numbers! I'll start from the assumptions that: the embankment is at rest light travels at c with respect to the embankment then show that in the mathematical world of time dilation and length contraction: The train observer can't tell how fast he's going. His best measurements tell him he's at rest. He can't synchronize his clocks with the embankment clocks. His best synchronization methods make his clocks out of sync with the embankment clocks The clocks he synchronized as well as he possibly could tell him that the lightning strike at the front of the train happened before the lightning strike at the back of the train. I'll go one step at a time, and wait for your questions and corrections before proceeding. In return, I expect that if I am able to do this to your satisfaction, then you will agree: that Einstein's world is a logically consistent world, and that if actual measurements in the real world match Einstein's world better than your own conceptual model, then your own conceptual model is wrong at relativistic speeds. Agreed? Motor Daddy05-10-11, 08:26 AMWe are using clocks, rulers, and light to measure with. We've shown that using the speed of light, and light travel time, that the embankment was at a zero velocity and that the train has a 4,958 m/s velocity. So far we've established that the lights hit the train observer at different times. We've also established that the train observer doesn't know the velocity of the train, or even if the train is at a zero velocity. The only thing he knows for sure is that the lights hit him at different times, and that he is at the midpoint of the train. Carry on with your measurements, like you agreed. If you can establish time dilation and length contraction in the train frame, by all means, go for it. I know how to measure from within the train, do you? origin05-10-11, 08:40 AMJames. I am arguing Einstein is wrong, why would I use his methods, or postulates? Here is the problem - you are doing more than saying Einstein is wrong, you are saying that real measurements of the speed of light are wrong. Special Relativity was Einstiens theory that expalined the consequences of the actual measurements of the speed of light. Particularly the aspect that regardless of the reference frame the speed of light is always measured as c. You disagree with this real world result (whether you realize it or not). You think that the speed of light is a constant similar to the speed of sound. As an example; if you are on a train that is going .5 the speed of sound then any sound waves eminating from the train will move out in the direction of travel at .5 the speed of sound relative to the train, and will move out opposite to the direction of travel at 1.5 the speed of sound relative to the train. Measurements and experiments have shown (for over 100 years) that this is not the case for light. Regardless of the motion of the light source or the observer the speed will always be measured as c. On a train that is moving at .5c a head light will have the beam move at c relative to the train AND relative to an observer on the bank. Before any discussion of simultaneity can be considered you must explain why you are disregarding measurements of the speed of light. Or at least supply some evidence that your idea that the speed of light is somehow affected by the motion of the source. I have asked you for evidence of your conjecture several times and you have ignored these requests. Since this concept is central to your analysis I would think that you would want to address it. How about it? Pete05-10-11, 08:40 AMThis is my mathematical world, MD. In this mathematical world, moving clocks run slowly and moving rulers are contracted. You agree that the train clocks are moving. Therefore they run slowly, whether the train observer knows it or not. Agreed? I know how to measure from within the train, do you? What do you suggest, MD? Motor Daddy05-10-11, 08:44 AMHere is the problem - you are doing more than saying Einstein is wrong, you are saying that real measurements of the speed of light are wrong. Special Relativity was Einstiens theory that expalined the consequences of the actual measurements of the speed of light. Particularly the aspect that regardless of the reference frame the speed of light is always measured as c. You disagree with this real world result (whether you realize it or not). You think that the speed of light is a constant similar to the speed of sound. As an example; if you are on a train that is going .5 the speed of sound then any sound waves eminating from the train will move out in the direction of travel at .5 the speed of sound relative to the train, and will move out opposite to the direction of travel at 1.5 the speed of sound relative to the train. Measurements and experiments have shown (for over 100 years) that this is not the case for light. Regardless of the motion of the light source or the observer the speed will always be measured as c. On a train that is moving at .5c a head light will have the beam move at c relative to the train AND relative to an observer on the bank. Before any discussion of simultaneity can be considered you must explain why you are disregarding measurements of the speed of light. Or at least supply some evidence that your idea that the speed of light is somehow affected by the motion of the source. I have asked you for evidence of your conjecture several times and you have ignored these requests. Since this concept is central to your analysis I would think that you would want to address it. How about it? I've done so many times on this board. The meter is defined by light travel time. They are inseparable. If you say light traveled for 1 second, it is irrefutable that it traveled 299,792,458 meters, because a meter is defined by light travel time. You can not separate the distance and time. Do you understand that? If not, learn it, it is CRUCIAL! It is also irrefutable that if you are 299,792,458 meters away from a light source when the light is emitted, if light doesn't impact you in 1 second, you moved, and from that you can calculate your velocity during that one second, because light always travels 299,792,458 m/s in a vacuum! Motor Daddy05-10-11, 08:54 AMThis is my mathematical world, MD. In this mathematical world, moving clocks run slowly and moving rulers are contracted. You agree that the train clocks are moving. Therefore they run slowly, whether the train observer knows it or not. Agreed? What do you suggest, MD? Pete, are you suggesting that you are incapable of establishing time dilation and length contraction in the train frame? Are you now wanting to implement something that you haven't shown with actual measurements? We are dealing with actual measurements of distance and time using light. No magic tricks or illusions are accepted in this example. Show me your measurements on the train using light, clocks, and rulers, and any other apparatus you need to sync the clocks. Pete05-10-11, 09:10 AMOne step at a time, MD. We'll get to measurements on the train when we've agreed on the current step. In this mathematical world, the moving clocks on the train tick slowly. At t=0.000, the train observer's clock at M' reads t'=0.000, . At t=16.67792893852027 ns , the slow M' reads 16.67792893623949 nanoticks (would it help if I say 'ticks' instead of 'seconds'?) At t=16.67848059041821 ns , the slow M' reads 16.67848058813736 nanoticks. Agreed? Motor Daddy05-10-11, 09:14 AMOne step at a time, MD. We'll get to measurements on the train when we've agreed on the current step. In this mathematical world, the moving clocks on the train tick slowly. At t=0.000, the train observer's clock at M' reads t'=0.000, . At t=16.67792893852027 ns , the slow M' reads 16.67792893623949 nanoticks (would it help if I say 'ticks' instead of 'seconds'?) At t=16.67848059041821 ns , the slow M' reads 16.67848058813736 nanoticks. Agreed? I don't understand. The train observer has clocks on the train that tick as one. Where does the difference come in play? You say "At t=16.67848059041821 ns , the slow M' reads 16.67848058813736 nanoticks." So are you saying that one clock on the train clicks t=16.67848059041821 ns, and the other clock on the train clicks 16.67848058813736 nanoticks??? So, one clock on the train clicks slower than the other clock on the train?? :shrug: Pete05-10-11, 09:19 AMI don't understand. The train observer has clocks on the train that tick as one. Where does the difference come in play? No, so far only one train clock has been described. You say "At t=16.67848059041821 ns , the slow M' reads 16.67848058813736 nanoticks." So are you saying that one clock on the train clicks t=16.67848059041821 ns, and the other clock on the train clicks 16.67848058813736 nanoticks??? I'm saying that after 16.67848059041821 seconds (you can measure this using embankment clocks if you like, because we know that they're sync'd and not dilated), the M' train clock reads 16.67848058813736 nanoticks. Motor Daddy05-10-11, 09:20 AMI have to go now. That will give you some time to think about it. See you soon. Pete05-10-11, 09:40 AMSee the last post on the previous page. I'm working under the assumption that the embankment is at absolute rest, because I thought you would be able to grasp that intuitively. When I talk about times, I'm talking about absolute times as defined by embankment clocks, and when I talk about distances, I'm talking about absolute distances as defined by embankment rulers. I am not going to talk about times or lengths in the train frame for some time yet. First, I will show what measurements can and can't be made by the train observer. Then, I will construct the measurement framework that we call the train frame. Then, I'll show that in that frame, embankment rulers are measured to be short, and embankment clocks are measured to run slowly and out of sync. But one step at a time. Good night. Farsight05-10-11, 10:30 AMMight I assist? To reach some agreement in this discussion might I suggest that you say that all clocks are light clocks, and that all rulers and other solid bodies are electromagnetic in nature. ...You think that the speed of light is a constant similar to the speed of sound. As an example; if you are on a train that is going .5 the speed of sound then any sound waves eminating from the train will move out in the direction of travel at .5 the speed of sound relative to the train, and will move out opposite to the direction of travel at 1.5 the speed of sound relative to the train...Think about what you'd measure if you were in essence "made of sound". See The Other Meaning of Special Relativity (http://www.classicalmatter.org/ClassicalTheory/OtherRelativity.doc). It talks about matter waves, gives the analogy of a submariner using a sonar clock, and says: "This might seem like an odd sort of clock, but consider the standard definition of a second, which is 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.3 If we regard the cesium atom as a kind of optical cavity which resonates at the prescribed frequency, then this is quite similar to our sonar clock. Consider also the definition of the meter, which is the length of the path traveled by light in vacuum during a time interval of 1/c =1/299,792,458 of a second.3 So we do in fact equate length with wave propagation time just as our hypothetical sailors do, and the quantity c is simply a unit conversion factor". Motor Daddy05-10-11, 11:04 AMNo, so far only one train clock has been described. Good, so one clock can't run slow, because it has nothing to compare to. It ticks, that's it. I'm saying that after 16.67848059041821 seconds (you can measure this using embankment clocks if you like, because we know that they're sync'd and not dilated), the M' train clock reads 16.67848058813736 nanoticks. Are you saying the train observer can use the embankment's clocks to compare to? That's strange, first you say the train observer has no way of knowing if he has a velocity or not because he isn't aware of the embankment, but then you change the story and say the train observer can compare his clocks to the embankment's clocks. Which is it, Pete, is the train observer aware of his surroundings (ie embankment and tracks) or is he clueless? By the way, when you say a clock runs slow, you really mean that another clock is the standard, and the "slow" clock is substandard. origin05-10-11, 11:29 AMI've done so many times on this board. The meter is defined by light travel time. They are inseparable. If you say light traveled for 1 second, it is irrefutable that it traveled 299,792,458 meters, because a meter is defined by light travel time. You can not separate the distance and time. Do you understand that? If not, learn it, it is CRUCIAL! My point is that apparently you do not understand that! You stated: If the train has a .5c velocity going down the tracks, and the train turns on a headlight that's located at the front of the train, 1 second later the light will be 149,896,229 meters in front of the train. Actual experimental measurements show your conclusion to be wrong. The light will move at 299,792,458 meters/sec relative to the train so the light will be 299,792,458 meters in front of the train 1 second later. What is your evidence that this is not correct. Beside your 'gut feeling' that is. Motor Daddy05-10-11, 11:42 AMActual experimental measurements show your conclusion to be wrong. The light will move at 299,792,458 meters/sec relative to the train so the light will be 299,792,458 meters in front of the train 1 second later. What is your evidence that this is not correct. Beside your 'gut feeling' that is. Really, is that what experiments show? So let's get this straight. A train is traveling down the tracks at .5c. As soon as the front of the train with a headlight aligns with a line on the tracks the headlight turns on. How far from the line is the front of the train after 1 second? How far is the light from the line after 1 second? Tach05-10-11, 12:09 PMHow far from the line is the front of the train after 1 second? 150,000m How far is the light from the line after 1 second? 300,000m. Are you still struggling with this? Motor Daddy05-10-11, 12:15 PM150,000 km 300,000 km. Are you still struggling with this? Correct, so the light is 150,000 km in front of the train after 1 second, as I already explained. Origin is the one struggling. origin05-10-11, 01:22 PMReally, is that what experiments show? Yes. So let's get this straight. A train is traveling down the tracks at .5c. As soon as the front of the train with a headlight aligns with a line on the tracks the headlight turns on. How far from the line is the front of the train after 1 second? How far is the light from the line after 1 second? It is rather simple to calculate how far in front of the train the light will be from the reference frame of the train, so lets do that. The speed of the light relative to the train is 299,792,458 meters/sec. So lets do the math: 299,792,458 meters/sec X 1 sec = 299,792,458 meters The light will be 299,792,458 meters in front of the train in the train's reference frame. Motor Daddy05-10-11, 01:34 PMYes. It is rather simple to calculate how far in front of the train the light will be from the reference frame of the train, so lets do that. The speed of the light relative to the train is 299,792,458 meters/sec. So lets do the math: 299,792,458 meters/sec X 1 sec = 299,792,458 meters The light will be 299,792,458 meters in front of the train in the train's reference frame. You didn't answer my questions: How far from the line is the front of the train after 1 second? How far is the light from the line after 1 second? We are using the tracks in this thread as the tracks, which have already been tested with light to be zero velocity. Answer the questions. Post ReplyCreate New Thread