Tom, The concept of a reference frame is a <b>very</b> simple one. Most people grasp the concept intuitively. But you can't seem to do even after it has been explained to you almost continuously for days on end. I repeat: <b>A reference frame is a point of view</b>. Nothing more, nothing less. In your example you can consider the energy in the reference frame of the 1 kg mass, or the frame of the 2 kg mass, or the centre-of-mass frame of the system, or from the point of view of an observer flying at 45 degrees to the line of collision at 0.567 times the speed of light. That is your choice, which you are free to make. The measurements of energy you make will be different depending on your choice. The "observer" does not have to be a real thing. Think of "the observer" as a God who watches events unfold from a distance. That God can choose to sit on the 1 kg mass and watch, or sit on the 2 kg mass and watch, or move in some relative way to both the masses. The important thing is that the observer is measuring and watching the process from some point of view. What you continually fail to do is to specify where this Godlike observer is and what he or she is doing. To answer <b>any</b> problem of this type, the very <b>first </b> thing which needs to be done is to specify the frame of reference of the observer. Then you can set out the rest of the problem. Most of the time, you simply ignore the need for an observer. You keep saying there is an absolute frame of reference. That would imply that there is a Godlike person sitting absolutely still whilst everything else in the universe moves around him or her. He or she never moves. Yet you cannot specify how to determine the state of motion of any object (such as your 1 kg mass) relative to this mythical absolute observer. The fact is, there is no absolute observer. The state of motion of <b>any</b> observer relative to the system of interest must always be specified in order to be able to work out an answer to a problem. You're inconsistent. Sometimes you assert that one or another reference frame in a problem is the absolute observer. For example, when you argue that when you drop a rock to the ground it is "really" the rock which moves and not the Earth, you are in effect sayng that the Earth is your absolute frame of reference. But the Earth <b>isn't</b> an absolute frame, because we know it moves relative to the sun (to take one example). At other times, you assert that the "absolute" observer is somehow removed from the action. I suspect, for example, that in the case of your two masses moving towards each other, you have some picture of an absolute observer sitting "at rest" somewhere between the two rocks, watching them both move. Again, this is a wrong picture. If the only things in your hypothetical universe are two rocks and an observer, who can say which ones are moving and which ones aren't? Nobody. The best we can do is to say which ones are moving relative to the other ones. I hope I don't have to explain this to you yet again at some future time. If I find that is necessary, I will refer you back to this post.
Tom, Regarding your clock synchronisation example, you have once again assumed one particular frame of reference - the frame of reference of the clock at the centre. In that frame of reference, your argument is 100% correct down to where you say: <i>In other words logic dictates that time slowed down equally for both clocks, and therefore they are synchronized.</i> That conclusion is true, from the specific frame of reference of the central clock. The two other clocks are synchronised in that frame of reference. You then say: <i>However, Einstein would argue that they can't be synchronized because, in each of their frames of reference, the other clock is moving at a high speed.</i> Here, you've changed reference frames and concluded that relativity says that the clocks are not synchronised in other reference frames. That is also correct. Can you see that there is no conflict between the clocks being synchronised in one reference frame and not synchronised in another reference frame? Relativity tells us that that <b>must</b> be the case. It is not a valid argument against relativity that this result goes against your gut feeling or "common sense". It is observed experimentally that this relativistic result is correct.
"""I repeat: A reference frame is a point of view. Nothing more, nothing less. """ hum, didn't know that Please Register or Log in to view the hidden image! That's the problem, endless points of view are not welcome in science, it has to be objective. """The important thing is that the observer is measuring and watching the process from some point of view.""" """Most of the time, you simply ignore the need for an observer. """ without an observer, everything would still be there identically, just a reminder """You keep saying there is an absolute frame of reference.""" maybe light in some sense """That would imply that there is a Godlike person sitting absolutely still whilst everything else in the universe moves around him or her. He or she never moves.""" Can you say that this is impossible? """Yet you cannot specify how to determine the state of motion of any object (such as your 1 kg mass) relative to this mythical absolute observer.""" --> light? """The fact is, there is no absolute observer.""" how do you know that? did you do some kind of an experiment? """You're inconsistent.""" You too: Define motion. """"Sometimes you assert that one or another reference frame in a problem is the absolute observer. For example, when you argue that when you drop a rock to the ground it is "really" the rock which moves and not the Earth, you are in effect sayng that the Earth is your absolute frame of reference.""" indeed, in some sense it is to say it differently: it knows point a goes to point b, but it can't tell if it passed from a --> (1,1) --> (2,1) --> b or from a --> (1,2) --> (2,2) --> b """But the Earth isn't an absolute frame, because we know it moves relative to the sun (to take one example).""" yes and if its motion didn't change towards the sun than it is the rocks motion who caused this to happen
Misconceptions Hi all, c'est moi, "It seems that the Einstein fanclub is in contradiction with each other." Please cite Q's and my quote in the correct context: we both said that a third observer is required to calculate the energy left by the explosion. When Tom asked Q what energy that third observer detected, Q responded that the question was meaningless, in the sense that any third observer will measure a different energy. I then repeated that a third observer is required anyway. There is no contradiction if you read everything correctly. Tom, "If the energy is released as photons(like a matter-antimatter reaction) I'm pretty sure that all observers would detect the same amount of photons. To assume that one observer would only see five photons while the other observer would see one million photons, sounds very illogical." Very true, however, the difference arises because every observer will measure a different amount of kinetic energy from their respective point of view (because of the different relative motion to different observers), but since you said... "As I have indicated in a another thread, I don't consider kinetic energy, energy at all. Kinetic energy is something that physicists use to balance there formulas. Therefore, I wouldn't be surprised if it was relative(considering that it doesn't exist in my frame of reference)" ... I don't think you will buy that explanation. Bye! Crisp
James R, In a single frame of reference, relativity doesn't seem flawed. However, if you merge multiple frames of reference into one, or if you split one frame of reference into multiple frames of reference, you will find that relativity breaks down. You may ask how do you merge multiple frames of reference into one?? I know of three ways: 1) You slow down all objects in all of the frames of reference to a constant speed. Since they are all now moving at the same speed, they can all be considered to be in the same frame of reference. 2) When the same object is present in two or more frames of reference. In other words, multiple frames of reference are linked by a single object. 3) When multiple objects combine to form one object. Example: two particles combine to produce one particle. This is similiar to the example I have provided on this thread. In all three of the cases I have provided above, the relativity of the different frames of reference contradict each other. Example of 2: If you drop a rock, does the rock travel towards the Earth or does the Earth travel towards the rock??? Relativity claims that both frames of reference are correct. Now if you drop a rock on the other side of the Earth, you still don't know whether the rock is travelling towards the Earth, or whether the Earth is travelling towards the rock. Relativity would claim that in this example, both frames of reference are correct. However, if you drop two rocks on opposite sides of the Earth at the same time, you will find that certain frames of references are wrong. You know that the Earth can't move to meet both rocks at the same time(because the Earth doesn't expand), so the frame of reference for at least one of the rocks has to be wrong. The more rocks you drop from different locations on the Earth, the more frames of reference are proved incorrect. In other words, what happened here was that The Earth linked multiple frames of reference together. Using the Earth as the link, you can prove which frames of refernce are correct and which ones are wrong. Example of 3: Let's say that the two metal balls, from the problem I provided at the beginning of this thread, were to merge into 1 larger ball. What frame of reference would this merged ball be in??? Would it be in the frame of reference of the 1 kg ball, the 2 kg ball, or neither??? If there was no conversion of mass to energy during the collision, would the resulting ball weigh 4.29 kg or 5.58 kg. The above example is what happens when frames of reference merge. Relativity is always wrong in these cases unless all the objects in all the different frames of reference weigh the same. That's all I'll say for now. I'll wait for you and Crisp to respond before I post more. Tom
c'est moi: Most of your post is not worth responding to, but I'll comment on one thing. I suggest you read the entire thread to get up to speed here. I said: <i>That would imply that there is a Godlike person sitting absolutely still whilst everything else in the universe moves around him or her. He or she never moves.</i> You said: <i>Can you say that this is impossible?</i> No, of course not. Just unnecessary. Can you say that my having a purple dragon called Herbert living in my garage is impossible?
Tom, Your entire post is based on further misunderstanding of frames of reference. An object does not exist in only one frame of reference at a time, but in a potentially infinite number of frames of reference. The object itself does not change when you change your point of view. I can watch you walk down the street from behind you, in front of you, off to one side, from a car driving past, or whatever. It doesn't change anything about you, only about how I see you. Changing reference frame is just like changing camera angle - taking a shot from a different camera. Your notion of "combining" reference frames makes no sense. Different reference frames are different points of view. Combining them would be like seeing things from two points of view at the same time. You can only look from one frame of reference at a time. You can select which camera you want to use, but turning on two cameras at once just results in an overlapped, mixed up picture. To take one example, you say: <i>1) You slow down all objects in all of the frames of reference to a constant speed. Since they are all now moving at the same speed, they can all be considered to be in the same frame of reference.</i> No. Even when they were travelling at different speeds, they were still all "in" the frame of reference you chose at the start. Nothing changes about the frame of reference unless you pick a different camera to watch the action. The speeds of the objects "in shot" change, but the camera angle stays the same unless you move the camera or change to a different camera. Now to your examples.... <i>Example of 2: If you drop a rock, does the rock travel towards the Earth or does the Earth travel towards the rock???</i> <b>Which camera are you using? The one on the Earth or the one attached to the rock?</b> <i>Example of 3: Let's say that the two metal balls, from the problem I provided at the beginning of this thread, were to merge into 1 larger ball. What frame of reference would this merged ball be in???</i> Whichever one you choose. Hit the button for camera 1 and it's in camera 1's reference frame. Select camera 2 and it's in camera 2's reference frame.
Prosoothus That's all I'll say for now. I'll wait for you and Crisp to respond before I post more. What am I, chopped liver ? Please Register or Log in to view the hidden image! Let's use a Cartesian plotting system for your example. We'll say that the event that is considered the moment of impact between the (1) and (2) kg. balls is given the coordinate (0,0,0). This coordinate can be considered a reference frame, or a point of view (you may use James R analogy of a godlike entity if you wish but I think the theists might have something to say Please Register or Log in to view the hidden image!). Using this system, plug in any number of coordinates you wish; (10,10,10) - (-4,280.-35) - etc... Each set of coordinates can be considered a reference frame, or a point of view of the event. The godlike entity may view the event from any one of these coordinates, and from each coordinate will get an entirely different view of the event. He will view the event as an impact of the two balls, but will view it from different angles, above, behind, below, near, far, etc.. As you can see there are endless amounts of reference frames in which to view the event. You may have a godlike entity for each and every point of view (FOR) observing the event at the same time. Every godlike entity will view the event differently than the next. Some entities will be very near one another and their view of the event will have subtle differences, but differences nontheless. As you can see, it is not possible to merge one reference frame with another into a single reference frame. One set of coordinates cannot be merged with another. That is like saying you can see the event from two points of view or two sets of coordinates at the same time. One observer has one point of view or one FOR, no more, no less. You amy use this system with the Earth and rock example as well.
James R, Stop avoiding my question. The 1 kg and 2 kg balls no longer exist, so the frames of reference for them don't exist anymore. There is only one larger ball remaining after the collision, nothing else. According to this resulting ball's frame of reference how much does it weigh 4.29 kg or 5.58 kg?? If the answer is both, then under which frames of reference when the original balls are gone??? And what cameras are you talking about, there is just one ball left after the collision?? Tom
Q, If an electron smashes into a proton and creates a neutron, which frame of reference is the neutron in??? Is it in the electron's or is it in the proton's original frame of reference??? Where did the frames of reference for the electron and the proton go?? They merged, that's where they went. If you have a different explanation, please share. Tom
Tom, <i>Stop avoiding my question.</i> I'm not. It has already been answered. The energies measured in the different reference frames are different depending on which frame you use. You complain that the number of photons emitted should not change, and I agree with you. What actually happens is that a particular number of photons is emitted, but those photons have different energies in different reference frames. <i>The 1 kg and 2 kg balls no longer exist, so frames of reference for them don't exist anymore.</i> What's this "frames of reference <b>for them</b>" stuff all about? I just explained to you how reference frames are independent of objects. Please re-read my previous 2 posts. Think about them. It's easy when you try. <i>And what cameras are you talking about, there is just one ball left after the collision??</i> Whichever cameras started viewing the process. Please re-read my previous two posts explaining this analogy and reference frames in general. Think about it.
Prothoosus Let's say the electron was at coordinate (10,10,10) and the proton was at coordinate (-10,-10,-10). They were both moving towards the coordinate (0,0,0) where they will impact and create the neutron. Here we have three separate reference frames and three different points of view. And remember I said that each observer can have only one point of view or FOR. As the electron and proton move towards coordinate (0,0,0), along with their observers who are sitting atop of the electron and proton, their sets of coordinates will change, hence the FOR will change until they impact. Once they've impacted all three observers will now share the reference frame from coordinate (0,0,0). You may say this is the merging of reference frames into one single frame and that is somewhat correct. All three observers are now situated at coordinate (0,0,0) and they share the same reference frame. However, what you're implying is that any other set of coordinates not in this position will view this impact the same way as the observers now situated at coordinate (0,0,0). That is not correct. Any other set of coordinates will view this impact differently. If the electron and proton observers were not sitting atop their respective 'vehicles', but instead remained at their set of coordinates (10,10,10) and (-10,-10,-10), there will always remain three separate frames of reference and hence three separate points of view. They will base their calculations relative to the coordinates of (0,0,0).
James R, let us keep it simple and leave that word "God" out. It is totally misplaced here. We are talking here about the possibility to escape motion. Again: Have you any proof that it is impossible for an observer to be motionless? Tell us of a law that would prevent this. Further, would you be so kind to define motion. I think it's the 5th time or so that I ask you this and unlike you, I don't like repeating the same thing over and over like some kind of programmed robot. Moreover, though I have no idea how to do it in practice, but why can't we use light as abs. FOR? Imagine that space is really an abs. FOR, like I believe, but that instead we *can* use it because we can somehow see space coördinates. In this case, you would all agree that we have found an abs. FOR that we can use. But what do we know about space? Maybe it is also moving as a system ... but does it matter? Likewise, if lightwaves would be gigantic, so gigantic that they would fill the whole universe with one ray and that further they'd all have the same frequency (colour), then you wouldn't be able to use light as FOR in experiments. It would all look the same. You'd know it's there but you wouldn't be able to use it. Likewise, space is black and gigantic, you can't use it, but it's there. But we could use light instead. It's motion is absolute, hence, it is an abs. FOR.
Cest moi In my opinion, the only phenomenon that comes close to what you're referring is the CMBR. But that permeates the universe. I'm not so sure if you could even consider it a FOR at all. I'd have to think about that one...
How does this happen? I agree with you that relativity contradicts common sense, that lowest form of logic. However, there are several good reasons for finding relativity to be a valid theory: A: Many insights in physics go against common sense. For instance, it seems that the sun revolves around the earth, not vice versa. Yet the earth orbits the sun. It seems that a lead cannonball should fall faster than a peice of paper of equal size. Yet they fall at the same speed. It seems that light should be either a particle or a wave. But it is both, depending on how one chooses to observe it. B: There is a great deal of evidence for general relativity. Not only does general relativity explain the orbit of Mercury, but it also is confirmed in observations of gravitational waves. See here for an overveiw of more evidence. See also here and here. Special relativity is confirmed by the existance of time dilation.
Hi c'est moi, "But we could use light instead. It's motion is absolute, hence, it is an abs. FOR." It is not the motion of light that is absolute, it is the *speed* of light. I'll give you some reasons why we can't use light as an absolute frame of reference: 1) For all practical situations, this frame of reference is simply no good. A particle collision (currently our best use for relativity and variants) is best described in other frames of reference (e.g. an observer travelling along with the centre of mass, or an observer for which the target is initially at rest). 2) From the basic experimentally verified fact that light travels at lightspeed, regardless of the observer, one immediatelly comes to a contradiction: in the frame of reference of the light, light does not travel at lightspeed. Physicists don't like exceptions. 3) From our current understanding of the universe (using the invariance of the speed of light) effects like time dilatation and length contraction immediatelly follow. For an observer moving along with the light, all events would occur instantaneously. Not quite practical to work with. These are just three reasons I can come up with without thinking, I'll leave it to others to add other reasons to the list. I really don't see why you or Tom would want to use light as an absolute frame of reference. If you accept that the speed of light is invariant for all observers, then you get troubles for using light as a FOR (points 2 and 3) - reason 3 is an immediate consequence of the invariance of the speed of light (i.e. it requires NO further assumptions whatsoever). So what you are really questioning here is the invariance of the speed of light. Oh, I almost forgot the most basic reason: 4) An absolute frame of reference is not required and would seriously complicate matters. Bye! Crisp
Xev, Just because clocks slow down when they travel at high speeds doesn't mean that time slows down. Maybe I went too far by saying that reality doesn't contradict common sense. I meant to say that reality doesn't contradict logic. As you pointed out, common sense isn't always logical. Common sense is influenced by people's perception of things while logic is not. Have you ever seen one of those old diagrams of our solar system where the Earth is in the middle and the Sun and the other planets revolve around it??? Do you know that you can use this diagram to predict the motion of the Sun and all the planets accurately. You might even be able to use it to predict the motion of the moon as well. Why is it that even though we all know that the Earth goes around the Sun, and not vice versa, this obviously incorrect model gives the correct results??? While some people on this board will argue that the Sun revolves around the Earth in the Earth's frame of reference, we know that it doesn't because of the laws of gravity. So, just because the theory of relativity can predict many physical phenomena, does that mean that it is the correct model? The answer is no. So how do you know what's the correct model?? The correct model has to pass these three tests: 1) It must be logical. 2) It must overlap reality 100%. If it doesn't, it either isn't correct or it isn't complete. 3) It must be simpler than all other models. Don't ever believe in a model that is not logical. After all, logic is all we have. Note: Cannonballs do fall faster than a piece of paper of equal size(in the Earth's atmosphere, of course. Please Register or Log in to view the hidden image! ) Tom
Tom I think I can see where you are going wrong. In the case of two objects on a collision course, like you have, it is better to take the frame of reference as the center point between them, where your ball or neutron is created. You can do the analysis from one frame or the other but the analysis is a lot harder than it should be. It also leads to apparent contradictions, as you realise. Most importantly, you can not just use the two equations you posted oiginally. You need the whole panoply of special relativity. Unless I miss my guess you have not studied it in great detail, just what people post here. If I'm wrong, I'm wrong, please tell me otherwise. Here's the wierd thing. You pick the frame of reference to be the 'absolute' one for the situation you are dealing with. It's a given that any such frame can be viewed as moving from any where else in the Universe. That is, in the real world anything else looking at the situation is probably moving as well. So, the basic equation you should be using here is the invariant kinetic energy. E^2=p^2 c^2 + 1/2 m^4 c^4 where m,p and E are functions of γ . Don't have the time to plug the numbers as I'm dealing with a sick child as well. There is nothing wierd about Relativity really. As james R has said before it is only about how one thing sees something rather than another point of view. It has some apparently daft ideas but that is because it a simplistic point of view really. But as Xev points out, it also works.
Crisp, C'est moi is questioning the invariance of the speed of light, just like I did in the "How accurate are atomic clocks??" thread. If you recall I used the formulas for time dilation and length contraction to prove that light's speed is not c in all frames of reference. You and James R, saw my results and saw that I was correct. Instead of admitting defeat, you and James R, claimed that I used the correct formulas for time dilation and length contraction, but that they weren't valid in the example I used (which, by the way, wasn't a complex example). I'm sorry, but I didn't fall for it, and I don't think that C'est Moi is falling for it either. Tom
Finally a real answer on this. Thanks Crisp. """It is not the motion of light that is absolute, it is the *speed* of light.""" Define motion. """1) For all practical situations, this frame of reference is simply no good. A particle collision (currently our best use for relativity and variants) is best described in other frames of reference (e.g. an observer travelling along with the centre of mass, or an observer for which the target is initially at rest)."""" you don't say why """2) From the basic experimentally verified fact that light travels at lightspeed, regardless of the observer, one immediatelly comes to a contradiction: in the frame of reference of the light, light does not travel at lightspeed. Physicists don't like exceptions.""" what does light do in the FOR of light? is it motionless? """3) From our current understanding of the universe (using the invariance of the speed of light) effects like time dilatation and length contraction immediatelly follow. For an observer moving along with the light, all events would occur instantaneously. Not quite practical to work with.""" Have you proof for this? """I really don't see why you or Tom would want to use light as an absolute frame of reference.""" It seemed logical. """If you accept that the speed of light is invariant for all observers,""" probably """then you get troubles for using light as a FOR (points 2 and 3) - reason 3 is an immediate consequence of the invariance of the speed of light (i.e. it requires NO further assumptions whatsoever). So what you are really questioning here is the invariance of the speed of light.""" maybe nobody explains why it is invariant unlike EVERYTHING else we know of btw, doesn't time dilation cause a change in the of speed of light --> time slows down hence motion also yes it slows down in our FOR but wasn't light supposed to be independant of any FOR? contradiction? """4) An absolute frame of reference is not required and would seriously complicate matters.""" A new theory is required to perform objective and logical science which both explains and predicts. Physicians should also understand the importance of philosophy for their physics, which most of them don't. Not only the results matter, understanding the results is far more important. Understanding and interpretting them always involves philosophy. Philosophy overrules physics and not the other way around, it's that simple.
