On the idea of time in physics-relativity

[Neddy Bate]

MMX does not compare two frames, so it is lacking the one thing in the TE that exposes relative simultaneity. Again, the emission and detection events of each path occur at the same places and times, which no observer would disagree on. The expectation of the waves being out of phase has nothing to do with the train in the TE.

But then the depth of your ignorance is no longer surprising.



The only way both flashes could be observed as simultaneous in both frames would be if there were a variable speed of light. Regardless of whether you have claimed this, your argument logically and physically demands it. You are just to blithely ignorant to bother looking at the facts. You know, the real world everyone tells you your woefully inadequate memory of simple pop-sci analogies is at odds with.

The train observer can and does assume himself to be at rest. But the only way for the flashes to be "sent to him at the same time" is for them to originate from the train frame. Reversing the TE to assume they do, the platform observer will then not see them as simultaneous.

It is physically impossible for both observers to receive the signals simultaneously when equidistant from their sources.

MMX and this TE are in complete agreement. You just do not readily see it because MMX does not address the factor in this TE which expose relative simultaneity.

Syne has made it very clear that P.Layman has been mistaken in his beliefs. The only question now is how P.Layman will deal with this. All he has to do is say something like, "Wow, thanks guys, you've taught me something about relativity of simultaneity." Then I'm sure everyone would say, "Wow, that Professor Layman guy is cool after all!" Or, P.Layman can say say something ... else...

 

[eram]

Syne has made it very clear that P.Layman has been mistaken in his beliefs. The only question now is how P.Layman will deal with this. All he has to do is say something like, "Wow, thanks guys, you've taught me something about relativity of simultaneity." Then I'm sure everyone would say, "Wow, that Professor Layman guy is cool after all!" Or, P.Layman can say say something ... else...

Unfortunately he's an incorrigible troll.

 

[Robittybob1]

MMX does not compare two frames, so it is lacking the one thing in the TE that exposes relative simultaneity. Again, the emission and detection events of each path occur at the same places and times, which no observer would disagree on. The expectation of the waves being out of phase has nothing to do with the train in the TE.

But then the depth of your ignorance is no longer surprising.



The only way both flashes could be observed as simultaneous in both frames would be if there were a variable speed of light. Regardless of whether you have claimed this, your argument logically and physically demands it. You are just to blithely ignorant to bother looking at the facts. You know, the real world everyone tells you your woefully inadequate memory of simple pop-sci analogies is at odds with.

The train observer can and does assume himself to be at rest. But the only way for the flashes to be "sent to him at the same time" is for them to originate from the train frame. Reversing the TE to assume they do, the platform observer will then not see them as simultaneous.

It is physically impossible for both observers to receive the signals simultaneously when equidistant from their sources.

MMX and this TE are in complete agreement. You just do not readily see it because MMX does not address the factor in this TE which expose relative simultaneity.

I see the person on the moving platform goes through the second light cone twice. If the animation and the speed of the platform were in the right proportion what difference would that make?
I see there is an intersection of the two light cones that crosses the path of the person on the moving platform so it looks like it would be possible to position the person at the right location that he intercepted this doubled portion and then both the person on the train and the platform would say the lightning struck simultaneously.
Can anyone else see this possibility (those simultaneous events would not be simultaneous themselves)?

 

[eram]

In that gif the relative velocity between the two observers exceeds the speed of light.

I see the person on the moving platform goes through the second light cone twice. If the animation and the speed of the platform were in the right proportion what difference would that make?
I see there is an intersection of the two light cones that crosses the path of the person on the moving platform so it looks like it would be possible to position the person at the right location that he intercepted this doubled portion and then both the person on the train and the platform would say the lightning struck simultaneously.
Can anyone else see this possibility (those simultaneous events would not be simultaneous themselves)?

Anyway, from the point of view of the person on the platform, he is closer to one end of the train, hence both lamps emit non-simultaneously for him to receive both signals at the same time.

Two events that are simultaneous in one frame can never be simultaneous in any other frame.

 

[Robittybob1]

In that gif the relative velocity between the two observers exceeds the speed of light.

Anyway, from the point of view of the person on the platform, he is closer to one end of the train, hence both lamps emit non-simultaneously for him to receive both signals at the same time.

Two events that are simultaneous in one frame can never be simultaneous in any other frame.

No the second observer only needs to be on one of the points where the light cones intersect. So he is relatively slow moving but is square onto the train when both of the intersecting light cones hits him. Both observers will say the events were simultaneous. So the way you say it is wrong. For I have just shown "two events that are simultaneous in one frame can be simultaneous in any other frame" But they wont agree on the timing of the simultaneity.
One will see it before the other but both will agree the two events were simultaneous, and they are in different frames.
So you need to say "Two events that are simultaneous in one frame can never be simultaneous in any other frame" differently.

 

[eram]

No the second observer only needs to be on one of the points where the light cones intersect. So he is relatively slow moving but is square onto the train when both of the intersecting light cones hits him. Both observers will say the events were simultaneous. So the way you say it is wrong. For I have just shown "two events that are simultaneous in one frame can be simultaneous in any other frame" But they wont agree on the timing of the simultaneity.
One will see it before the other but both will agree the two events were simultaneous, and they are in different frames.
So you need to say "Two events that are simultaneous in one frame can never be simultaneous in any other frame" differently.

I don't quite get what you mean. An "event" is the emission of a photon, for example. If the emission of both lamps is simultaneous in one frame, they cannot possibly be simultaneous in another.

 

[Write4U]

The experiment calls for "flashing lights located at the front and rear of a moving train"

http://i45.tinypic.com/zughar.gif

I am sorry, but I have a problem with this illustration. I have tried to look at this from both perspectives.
a) is a stationary train, flashing a light at its front and rear simultaneously as a moving train-station passes by?
b) the moving object is the train, but the flashing lights are at the train-station, located a train length apart, and flashing as the train moves by.

Does the illustration project an accurate view of the experiment? I feel really uneasy about this. Especially in view of "simultaneity".

 

[Write4U]

Perhaps I have a different visual as intended. In order to maintain simultaneity I see the lights on the train flash as the "observer on the train" passes the "stationary observer" and both are equidistant (but not the same distance) from the flashes.

Can someone modify that original .gif to reflect that scenario? I am curious if the radiation intersects would yield a different result.

 

[eram]

Perhaps I have a different visual as intended. In order to maintain simultaneity I see the lights on the train flash as the "observer on the train" passes the "stationary observer" and both are equidistant (but not the same distance) from the flashes.

Can someone modify that original .gif to reflect that scenario? I am curious if the radiation intersects would yield a different result.

In order to understand this you need to consider both frames, both points of view.

The speed of light is constant, the nature of events is the same, but simultaneity is violated.



If Bob receives both photons at the same time in his frame, he will also receive both at the same time in John's frame.

If the photon emissions happen simultaneously in Bob's frame, they will not be simultaneous in John's frame.

 

[Robittybob1]

anywhere where the two light cones intersect will give a simultaneous interpretation to the seeing the photons coming from the two events. Well it is quite clear from the animation that the intersection of the light cones spreads out in opposite directions from the mid point of a line between the two events (Points at the centres of the two circles can be connected with a straight line. 1. (do you see that and that is where the first observer (the mid point observer) is situated?)

After that the points of intersection of the two circles spreads out to either side of this mid point along a line orthogonal to the line between the centres. 2 (do you see that?)

So any one in a frame moving such that they coincide with these intersection points will also sense simultaneous events. 3 (do you see that?)

So it may be possible to arrange that many frames are coinciding with these points, I can't say "all frames will", but it certainly isn't zero. 4. (do you see that?)

The other frames will sense the simultaneous events but I agree they will sense this some time after the mid point observer. 5 (do you see that?)

So out of points 1,2, 3, 4 or 5, which ones can't you see?

 

[Write4U]

Draw me a .gif where the lights flash only when both observers are equidistant from the flash; then have the train (not the flash) continue instead of the station. And observe how the radiation from the single simultaneous flash reaches both observers.
At least it would show the experiment as specified. After that one can argue alternate illustrations.

Sorry, I am not trying to be presumptuous, its the bookkeeper in me...

 

[Pete]

The train observer can and does assume himself to be at rest. But the only way for the flashes to be "sent to him at the same time" is for them to originate from the train frame.

This is a misconception.
The light flashes do not have a particular frame of origin. They originate in all frames.
In Einstein's thought experiment, he made each flash come from an instantaneous lightning strike, to avoid confusion relating to motion of the originating light source.

Nice animation, but not representative of the situation.
The platform moves past the train at less than the speed of light.
One strike occurs as the front of the train passes the back of the platform.
The other strike occurs as the back of the train passes the front of the platform.

The only way for the flashes to originate at the same time in the train reference frame is if the platform's contracted length is the same as the train's proper length, instead of the other way around.

 

[Prof.Layman]

The only way both flashes could be observed as simultaneous in both frames would be if there were a variable speed of light. Regardless of whether you have claimed this, your argument logically and physically demands it. You are just to blithely ignorant to bother looking at the facts. You know, the real world everyone tells you your woefully inadequate memory of simple pop-sci analogies is at odds with.

A variable speed of light is not the only way that the flashes could be observed to be simultaneous. They did away with the aether theory, that says that there is a background where light travels at the same speed from a single frame. This was then replaced by Einsteins notion of spacetime, where spacetime dilation and contraction corrects for the speed of light in both frames.

The only type of diagram that I think could serve as an accurate depiction of the speed of light would be Minkowski Diagrams . Like in my derivation in post #266, it assumes that distance is c t. It is also said that Minkowski Diagrams are accurate when dealing with these kind of problems. So most of the confusion here is just caused by the use of inaccurate diagrams. It is like you have all taken a laymans descriptions, in a book targeting layman, and then have posted it up as being actually science. If you wanted to know what the real science says about this problem would would want to use Minkowski Diagrams .

It is really like you guys are saying that there is an aether. Having a difference of relative motion relative to photons is what aether theory says. So then everytime you say that there is a difference in relative motion relative to the photon you are just saying that there is really an aether. I think mazula would love to hear about this and these types of alternative theories, you should all rederict them to the thread Luminiferous-Aether-Exists! in the alternative theories section.

 

[wellwisher]

A variable speed of light is not the only way that the flashes could be observed to be simultaneous. They did away with the aether theory, that says that there is a background where light travels at the same speed from a single frame. This was then replaced by Einsteins notion of space-time, where space-time dilation and contraction corrects for the speed of light in both frames.

If C or the speed of light is constant, then d=C/t, where d=distance and t=time. Because the speed of light is finite and constant, any motion between source and reference will alter d (with without relativity) which means t is also altered. This precludes simultaneity at least within finite reference space-time.

At the speed of light, distance and time contract to a point-instant. This allows all distance and time to overlap therefore C reference sees universal simultaneity. This is the best reference to use if simplification is the goal. Finite reference has lags in distance and time and becomes much more complicated.

 

[Prof.Layman]

If C or the speed of light is constant, then d=C/t, where d=distance and t=time.

This is wrong. c is the speed of light, so then c is a velocity.

$$ v = \frac{d}{t} $$

$$ v t = d $$

$$ d = v t $$

$$ d = c t $$

The speed of light can just simply be replaced with velocity in this equation. But then instead of saying that it has different relative velocity, the speed of light is the same value in all frames. So instead of a different distance and time giving a different velocity, the same velocity gives different distances and times.

 

[hansda]

If they happen at the exact same time according to the observer, the observer will say they were simultaneous. But with a little more information he will quickly realize that out where the star happened to explode, no dog was yet existing to bark at its demise. Therefore, simultaneity is relative, wouldn't you agree?

Why do you assume that the dog does not exist at the star's demise? Assume that the dog is existing and barking throughout time.

In measuring simultaneity, would it matter what time of day the clock reads, or how fast it's ticking? No. All that's necessary is to determine that no delay has elapsed between the two events. An actual clock or timebase wouldn't necessarily be required since this is a gating function with a simple positive or negative result.

So, "relativity of simultaneity" is basically "relativity of two clocks positioned at different locations".

 

[origin]

I am trying to bring you up to speed about how the properties of light have changed over the past 100 years. The only thing you know about relativity is the relativity of simultaniety, I am saying that it is out dated...... The only place I think that is done is in Einsteins book and the internet. In any other book it will say that the beams of light will reach an observer in motion at the same time that is equidistant even if it is in motion! I think a lot of sites have allowed someone that only knew about the relativity of simultaniety from this book to teach everyone about SR, and has given a lot of people incorrect views on SR because of this..

I have looked and every book on special relativity that I have reviewed has a section on simultaniety. Every course syllabus that I have looked at has had a section on simultaniety.

That leads me to the unfortunate conclusion that you are a liar, a fool or you mispoke (miswrote?).

Just wondering which is it?

 

[Syne]

I see the person on the moving platform goes through the second light cone twice. If the animation and the speed of the platform were in the right proportion what difference would that make?
I see there is an intersection of the two light cones that crosses the path of the person on the moving platform so it looks like it would be possible to position the person at the right location that he intercepted this doubled portion and then both the person on the train and the platform would say the lightning struck simultaneously.

Both frames could possibly see two light signals as simultaneous,...

...but physics dictates that these could not be the same signals,...

...as the platform observer would not observe them to originate from the ends of the train.

With the train traveling less than c, the platform observer cannot reach the intersection of the two light spheres before the front one catches him. If both agree on simultaneity then both would disagree on the origin of the signals, which necessarily means that they cannot be comparing the observations of the same signals.

In that gif the relative velocity between the two observers exceeds the speed of light.

Corrected above.

No the second observer only needs to be on one of the points where the light cones intersect. So he is relatively slow moving but is square onto the train when both of the intersecting light cones hits him. Both observers will say the events were simultaneous. So the way you say it is wrong. For I have just shown "two events that are simultaneous in one frame can be simultaneous in any other frame" But they wont agree on the timing of the simultaneity.
One will see it before the other but both will agree the two events were simultaneous, and they are in different frames.
So you need to say "Two events that are simultaneous in one frame can never be simultaneous in any other frame" differently.

No, as shown above, spatially separated events that can be observed as simultaneous in one frame cannot be so in another. Any such mutually observation of simultaneity is necessarily of a different set of events.

 

[Prof.Layman]

I have looked and every book on special relativity that I have reviewed has a section on simultaniety. Every course syllabus that I have looked at has had a section on simultaniety.

Just wondering which is it?

I think I actually got it from reading about quantum mechanics not relativity.

 

[Syne]

This is a misconception.
The light flashes do not have a particular frame of origin. They originate in all frames.
In Einstein's thought experiment, he made each flash come from an instantaneous lightning strike, to avoid confusion relating to motion of the originating light source.

The origin of the flashes is necessarily either co-moving with the train or the platform. Here, I made them co-moving with the train. This is what is meant by them originating from one frame. Which frame the flashes are co-moving with or simultaneous in does not matter one wit in demonstrating relative simultaneity.

Nice animation, but not representative of the situation.
The platform moves past the train at less than the speed of light.
One strike occurs as the front of the train passes the back of the platform.
The other strike occurs as the back of the train passes the front of the platform.

The only way for the flashes to originate at the same time in the train reference frame is if the platform's contracted length is the same as the train's proper length, instead of the other way around.

The relative speed is corrected in the latest gifs I posted (excuse the earlier, hasty exaggeration). It is not necessary to take length contraction into account to depict the RoS, only relative speed and the constancy of the speed of light. The relativity of simultaneity is a consequence of the two postulates of SR, just like time dilation and length contraction.