Problem with relativity of simultaneity original example

[Doc Al]

You claim that A` and B` are different based on what? On the interpretation of M`? Ok,,, so why M` sees events in different time? because M` moves in the direction of B`-signal faster than than A`one,,, so why that happens? because you consider that from the embankment point of view,,, Pronto

The only data we are given is from the embankment point of view. Of course we'll use it!

In the Einstein scenario you are told that the lightning strikes are simultaneous in the embankment frame. That's the only information you are given. But that's enough to show that the train observers will see the lightning striking at different times. (It is shown, not 'assumed'.)

But if you see the experiment whwn A` and B` are involved ( also according to the embankment point of view),,, the matter changes clearly,,, pronto

I don't understand this statement. All frames agree that the light strikes M' at different times!

 

[Adel Makram]

i also agree about different timing at M` but not for A` and B`,,, let's say that M` wants to share his data with A` and B`,,, then he sends light signals once he received ( equivalent to using M`-mirror),,, if M` sees B` before A` then according to the train FOR, B` should also receive the reflected signal before A`. But as seen from the external observer, no such thing happens, why? because this time, the light has to travel a bit longer distance to reaches B` than A` and finally they will be coincide their measurments

 

[Doc Al]

i also agree about different timing at M` but not for A` and B`,,, let's say that M` wants to share his data with A` and B`,,, then he sends light signals once he received ( equivalent to using M`-mirror),,, if M` sees B` before A` then according to the train FOR, B` should also receive the reflected signal before A`.

He does! According to the train clocks, B' receives the signal before A'.

But as seen from the external observer, no such thing happens, why? because this time, the light has to travel a bit longer distance to reaches B` than A` and finally they will be coincide their measurments

It's certainly true that according to embankment clocks the light strikes the observers at the ends of the train at the same time. But not according the train clocks. That's the entire point of the thought experiment--to illustrate the relativity of simultaneity.

 

[Adel Makram]

But what happens actually is because A` and B` coincide their measurements after receiving the reflection from M`,,, they should do so both for the ground observer and for the train ( for the ground it is easy to imagine that and for the train this should be done after having a communication with each other). There is no point when you say that M` should be have different timing for both frames of references and on the other hand, A` and B` should not. As long as, the All matter is judged from the external observer point of view :)

 

[Doc Al]

But what happens actually is because A` and B` coincide their measurements after receiving the reflection from M`,,, they should do so both for the ground observer and for the train ( for the ground it is easy to imagine that and for the train this should be done after having a communication with each other).

The folks on the train measure distance and time using their own clocks, of course. Everyone uses their own clocks! What you want to do is compare what the train clocks would say to what the embankment clocks would say. There's nothing special about the embankment clocks. That's one of the key aspects of relativity.

There is no point when you say that M` should be have different timing for both frames of references and on the other hand, A` and B` should not.

The difference between them is that arrival of the light at M' happens at the same location on the train, but A' and B' are at different ends of the train. That makes a big difference! If two things happen at the same time at the same place (to M', for example), then everybody in every frame agrees that they happen at the same time. (And using their own clocks, of course.) But if two things happen at the same time but at different locations in one frame, they will be seen to happen at different times in another frame.

As long as, the All matter is judged from the external observer point of view :)

Uh, no.

 

[Adel Makram]

Firstly: I guess that you should correct the word in your second passage,,, that if 2 things happen at different times at the same location ( for M`) because M` timing is different for every FOR
Secondly: it seems that you do not examine the principle of relativity of simultaneity; you just use it as it was proposed. The real test of this principle will not be achieved unless you complete the thought experiment I proposed. Please do not stop at the stage when the light is just received by M`, complete the story,,, A` and B` have their own local times
Thirdly: the whole issue of relativity of simultaneity is based on 1 fact and 2 interpretations. The fact is M` receives the signal at different time, it was the real observation made by the external observer. This observation has 2 interpretations: for the external one: light from B` reaches M` faster than A` . For the train ‘s observer: B` happens before A`. After reflection from M`-mirror back to both ends, the light reaches A` and B` at the same time ( this is another fact similar to the first one). This time the interpretation made by the external observer: Light to A` catches up the light to B` and appears at both times. For the train observer: ( A` at the same time as B`),,,, done

 

[Doc Al]

Firstly: I guess that you should correct the word in your second passage,,, that if 2 things happen at different times at the same location ( for M`) because M` timing is different for every FOR

No, I meant what I said. If the light from A' and B' reaches M' at the same time, then every frame agrees that the light arrived simultaneously. And if, as in our case, the light reaches M' at different times, then every frame agrees that the light arrive at different times. This is basic and must be understood before continuing. Please confirm that you understand this.

Secondly: it seems that you do not examine the principle of relativity of simultaneity; you just use it as it was proposed. The real test of this principle will not be achieved unless you complete the thought experiment I proposed. Please do not stop at the stage when the light is just received by M`, complete the story,,, A` and B` have their own local times

We are discussing Einstein's thought experiment. If you have proposed a different one, you must define it properly.

Thirdly: the whole issue of relativity of simultaneity is based on 1 fact and 2 interpretations. The fact is M` receives the signal at different time, it was the real observation made by the external observer.

Right. And all frames, not just the 'external' one, agree on this.

This observation has 2 interpretations: for the external one: light from B` reaches M` faster than A` .

Everyone agrees that the light from B' arrived at M' before the light from A'.

For the train ‘s observer: B` happens before A`.

Right: according to the train frame, the lightning hit B' before it hit A'.

After reflection from M`-mirror back to both ends, the light reaches A` and B` at the same time ( this is another fact similar to the first one).

No it doesn't (at least not in the train frame). How could it? A' and B' are equidistant from M'.

This time the interpretation made by the external observer: Light to A` catches up the light to B` and appears at both times.

Sure, from the 'external' frame.

For the train observer: ( A` at the same time as B`),,,, done

False. Done!

You have to explain why you think that if the light reflects from M' at different times that it can somehow reach A' and B' at the same time. All of this is within the train frame--it has nothing to do with the 'external' frame.

 

[Adel Makram]

You have to explain why you think that if the light reflects from M' at different times that it can somehow reach A' and B' at the same time. All of this is within the train frame--it has nothing to do with the 'external' frame.

This is a fact observed by the eyes of all observers ( similar to the first fact that M` timing was different). My explanation is the train observer must recognize that because B` should have received the reflect signal earlier than A` which did not happen, then the train must be moving in the direction of B` ( which is against the principle of relativity,,, or the Mickelson famous experiment would be +ve)
However, because I still believe in the principle of relativity, I can understand that if the light source was originated from B` before A` at the local arrangement and this time based on the MIND of the train observer (not the ground one) , then the reflected light should also reaches B` before A`,,, because in this example I consider the train FOR is inertial one and the laws of physics and the speed of light are invariant
This means that the 2 situations are different. It is different to arrange the experiment from the external point of view with the lightning is a primarily external source than to arrange the timing based on the train observer local arrangement which is of course would maintain the principle of relativity
This raises up a conclusion that any sort of Transformation between the 2 FORs should be asymmetrical. And because the well known Lorentz T (LT) is symmetrical one, this means that LT is not true

 

[Doc Al]

This is a fact observed by the eyes of all observers ( similar to the first fact that M` timing was different).

No it's not. In fact it directly contradicts the fact that the light arrived at M' at different times.

In a thought experiment you cannot just assume whatever you like, you must provide an argument.

My explanation is the train observer must recognize that because B` should have received the reflect signal earlier than A` which did not happen, then the train must be moving in the direction of B` ( which is against the principle of relativity,,, or the Mickelson famous experiment would be +ve)
However, because I still believe in the principle of relativity, I can understand that if the light source was originated from B` before A` at the local arrangement and this time based on the MIND of the train observer (not the ground one) , then the reflected light should also reaches B` before A`,,, because in this example I consider the train FOR is inertial one and the laws of physics and the speed of light are invariant
This means that the 2 situations are different. It is different to arrange the experiment from the external point of view with the lightning is a primarily external source than to arrange the timing based on the train observer local arrangement which is of course would maintain the principle of relativity
This raises up a conclusion that any sort of Transformation between the 2 FORs should be asymmetrical. And because the well known Lorentz T (LT) is symmetrical one, this means that LT is not true

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[Adel Makram]

No it's not. In fact it directly contradicts the fact that the light arrived at M' at different times.

Let` s say that there is no observer in the middle of the train, only a place for M`-mirror. Now the light reflected from the mirror will reach A` and B` at the same time as seen by the external observer,,, So according to his thought projection regarding what would be observed by the A` and B` observers,,, why they should interpret that their timing of receiving the reflected signal are not the identical? and back to on of my earlier question, why the relativity of simultaneity is merely based on the existence of M` ?

 

[Doc Al]

Let` s say that there is no observer in the middle of the train, only a place for M`-mirror. Now the light reflected from the mirror will reach A` and B` at the same time as seen by the external observer,,,

Before worrying about external observers, first answer the question: According to train observers, if the light reflects from M' at different times, will A' and B' receive the reflections at the same time or at different times?

This is a very simple question which has nothing to do with changing frames or with Lorentz transformations.

 

[JDoolin]

Maybe the attached animation will help.

 

[Adel Makram]

According to train observers, if the light reflects from M' at different times, will A' and B' receive the reflections at the same time or at different times?

OK: first, according to train observers means what?

1) either means according to what would be expected from the train observers to see according to the external observer perspective ( remember again , all the thoughts is from the external observer point of view and I would like to call it thought projection),,, in this case A` and B` should receive the signal at the same time

2) Or means according to what would be expected from the train observers to see according to the train observers perspective ,,, in this case yes A` will be different than B`

 

[Adel Makram]

but the second one needs different arrangement than in our thought experiment ( because our thought experiment is merely depends on the thought projection of the external observer for all frames)

 

[Doc Al]

OK: first, according to train observers means what?

It means just what it sounds like it means: The train observers have synchronized clocks. When the light reaches them, they record the time of arrival on their clocks.

They certainly wouldn't look to an outside frame of reference to decide what their own clocks would read.

1) either means according to what would be expected from the train observers to see according to the external observer perspective ( remember again , all the thoughts is from the external observer point of view and I would like to call it thought projection),,, in this case A` and B` should receive the signal at the same time

Again, you are confusing the two different perspectives.

From the view of the 'external' observer: The light arrives at A' and B' at the same time according to external clocks, but not according to the the train clocks! The only way to make sense of this is to realize that from the view of the 'external' frame, the clocks used by the train observers are not synchronized.

2) Or means according to what would be expected from the train observers to see according to the train observers perspective ,,, in this case yes A` will be different than B`

Of course. So you agree that according to the train observers very own clocks, the light arrives at different times?

Everybody agrees on this! Even the external observer agrees!

 

[Doc Al]

but the second one needs different arrangement than in our thought experiment ( because our thought experiment is merely depends on the thought projection of the external observer for all frames)

Forget about 'thought projection'. Let's talk actual clocks.

 

[Adel Makram]

Ok now I would like to extend the thought experiment a bit. I would like to show that the interpretation of train observers according to the arrangement made from the external observer point of view is different from the interpretation made when the arrangement made from the train observer point of view
The light from B` is relatively moving toward M` faster than A` . So for M`, he will see the light from B` is blue-shifted and from A` is red-shifted. But after reflection from M`-mirror, the amount of Doppler shifted from each direction is compensated again and appears not-shifted as measured by A` and B`. so A` and B` would communicate with each other and share their results which will be no Doppler shift for the arrival signal after reflection. But if the matter is judged from train observer arrangement, the coming blue-shifted signal from B` should remain blue-shifted after the reflection (because reflection will not change the color of the light) and the same for A`. So the communication between A` and B` will be different color or shifted-in short even though there would be a time delay between the arrival of signal to both ends (according to the common interpretation of the thought experiment) This is a paradox. Because the physical reality should remain invariant relative to all observers
To make it more objective, let`s put a another pair of reflecting mirrors but this time at A` and B`. And those mirrors should be adjusted to reflect the coming light from M` to a point equidistant from both ends but located outside the train ( like projecting onto a big screen so all observers can see). OK, so because the reflected rays from M` will be in phase, they will be projected from A` and B` mirrors onto the outer screen and forming an interference pattern with bright and dark stripes. For the external observer point of view, the train observers can see that interference pattern from his train window. But if train observers A` and B` see the events at different time and because the coming rays from M` still maintains the color of the original signal directed from both ends before reflection on M`, there must be a phase-change when the rays reflected from A` and B` and the interference pattern on the outer screen will be a superposition of rays and not just bright and dark strips. This makes a paradox. Because the interference pattern on the outer screen is invariant-physical reality and should be seen the same by all observers.
This indicates that the arrangement of the thought experiment according to the external observer ( with all his expectations about what M` interpretation of simultaneity is different from the arrangement that could be made according to the train observer per Se when the light just hits M` from B` direction before A` direction)

 

[Doc Al]

Ok now I would like to extend the thought experiment a bit. I would like to show that the interpretation of train observers according to the arrangement made from the external observer point of view is different from the interpretation made when the arrangement made from the train observer point of view

Are you claiming that the time recorded on the train observer's clocks when the light arrives depends on who views it?

The light from B` is relatively moving toward M` faster than A` . So for M`, he will see the light from B` is blue-shifted and from A` is red-shifted. But after reflection from M`-mirror, the amount of Doppler shifted from each direction is compensated again and appears not-shifted as measured by A` and B`. so A` and B` would communicate with each other and share their results which will be no Doppler shift for the arrival signal after reflection. But if the matter is judged from train observer arrangement, the coming blue-shifted signal from B` should remain blue-shifted after the reflection (because reflection will not change the color of the light) and the same for A`. So the communication between A` and B` will be different color or shifted-in short even though there would be a time delay between the arrival of signal to both ends (according to the common interpretation of the thought experiment) This is a paradox. Because the physical reality should remain invariant relative to all observers
To make it more objective, let`s put a another pair of reflecting mirrors but this time at A` and B`. And those mirrors should be adjusted to reflect the coming light from M` to a point equidistant from both ends but located outside the train ( like projecting onto a big screen so all observers can see). OK, so because the reflected rays from M` will be in phase, they will be projected from A` and B` mirrors onto the outer screen and forming an interference pattern with bright and dark stripes. For the external observer point of view, the train observers can see that interference pattern from his train window. But if train observers A` and B` see the events at different time and because the coming rays from M` still maintains the color of the original signal directed from both ends before reflection on M`, there must be a phase-change when the rays reflected from A` and B` and the interference pattern on the outer screen will be a superposition of rays and not just bright and dark strips. This makes a paradox. Because the interference pattern on the outer screen is invariant-physical reality and should be seen the same by all observers.
This indicates that the arrangement of the thought experiment according to the external observer ( with all his expectations about what M` interpretation of simultaneity is different from the arrangement that could be made according to the train observer per Se when the light just hits M` from B` direction before A` direction)

Sorry, but the Doppler shift is irrelevant to this thought experiment. All that matters is that the speed of light is the same in every frame.

 

[Adel Makram]

Are you claiming that the time recorded on the train observer's clocks when the light arrives depends on who views it?

Not exactly, what I meant to say is: no way to know how the times could be recorded by A` and B`based on the external observer expectation

Sorry, but the Doppler shift is irrelevant to this thought experiment. All that matters is that the speed of light is the same in every frame.

I did not mean to discuss the Doppler-shift experiment, this was just an example of how different outcomes of the thought experiment fools the expectation of the external observer regarding the way the train observers see how things proceed. Any way I am not very sad because no comment on the Doppler-part of the experiment. But I would be very disappointed when that would have come from Pioncare or Einstein if they were still alive

 

[Doc Al]

I did not mean to discuss the Doppler-shift experiment, this was just an example of how different outcomes of the thought experiment fools the expectation of the external observer regarding the way the train observers see how things proceed. Any way I am not very sad because no comment on the Doppler-part of the experiment. But I would be very disappointed when that would have come from Pioncare or Einstein if they were still alive

I did comment: It's irrelevant to Einstein's thought experiment. No one's getting 'fooled'; simultaneity is frame-dependent.

 

[Adel Makram]

I did comment: It's irrelevant to Einstein's thought experiment. No one's getting 'fooled'; simultaneity is frame-dependent.

1) The external observer can not make this statement without a M`-observer. If he can, it would be enough just A` and B` for him to reach the same conclusion
2) The relativity of Simultaneity based on the Einstein`s Thought Experiment is a personal speculation of the external observer, not a real principle of physics

 

[JDoolin]

This raises up a conclusion that any sort of Transformation between the 2 FORs should be asymmetrical. And because the well known Lorentz T (LT) is symmetrical one, this means that LT is not true

I don't think the Lorentz Transformation is "symmetrical" in the sense you are describing.

If you have two trains passing each other in opposite directions.

What are really simultaneous events on one train will appear to happen in consecutive order, back to front, from the other train.

What appears to happen simultaneous from the other train, is really happening in consecutive order from front to back from the same train.

(Edit: Caveats, Clarifications, Qualifications: I say "what is really happening" when I mean, watching events happen on your own train, whereas I say "what appears to happen" when describing events that happen on the other train. Of course, "what appears to happen on the other train" is still "really" happening, but I hope you can understand the gist. This also doesn't take into account any effects of the delay caused by the speed of light, so when I say "what appears to happen" that is after you've accounted for any speed-of-light-delay-effects, and calculating the object where it "was" when the light left it, not how it actually appears, which is the way this thought experiment is usually done.)

 

[Doc Al]

1) The external observer can not make this statement without a M`-observer. If he can, it would be enough just A` and B` for him to reach the same conclusion

You miss the point of the thought experiment. The purpose of using M' is just to make it easy to analyze the scenario. But the fact that A' and B' are hit by lightning at different times according to their clocks does not depend on having an observer at M'. All you have to agree upon is that the light flashes reach the middle of the train at different times. This is a simple fact agreed upon by all.

2) The relativity of Simultaneity based on the Einstein`s Thought Experiment is a personal speculation of the external observer, not a real principle of physics

Nonsense.

Please reread my comments at the bottom of post #39 before continuing.

 

[Adel Makram]

1) Again, the arrangement made by the external observer of the experiment and his expectation about what A` and B` would observer is different from the arrangement made by the train observer M` if M` conducts the experiment maintaining a time delay between emitting the light toward B` before A` ( in the second situation, the external observer can not be sure that the light from B` and A` would arrive him at the same time)
2) The Einstein thought experiment can not explain the Doppler-Paradox I proposed in comment #47

 

[Adel Makram]

The prediction that the light reaches A` and B` at different time is an indirect assumption made by the external observer. He used the fact that M` knows that light speed is constant and the reflected rays should reach both ends at different times. This is another common sense assumption similar to the pre-relativity common sense that the 2 events happening at the same time should be so for all observers,,, the external observer can`t give any visual evidence based on optics to prove that,,, in fact it might be impossible for him to see A` and B` at the same time and at different time. I also have no idea if there is any computer simulation that can show so,,, If the external observer wants to know whether A` and B` times are different, he should ask them once the lightning struck A` and B`

 

[Adel Makram]

Again, if the external observer considers what M` might see on one hand and what he sees on the other hand, the Doppler-paradox will emerge,,, this is similar to the statement that the external observer considers that M` knows that B` happens before A` and on the other hand sees that A` and B` occurs together at the same time. So the conclusion is: any optical arrangement made to know when M` see A` and B` happen in the train by the external observer will create a paradox, therefore the timing of A` and B` will remains just an assumption unless the external observer ask them directly once they receive the lightning

 

[Doc Al]

The prediction that the light reaches A` and B` at different time is an indirect assumption made by the external observer. He used the fact that M` knows that light speed is constant and the reflected rays should reach both ends at different times. This is another common sense assumption similar to the pre-relativity common sense that the 2 events happening at the same time should be so for all observers,,, the external observer can`t give any visual evidence based on optics to prove that,,, in fact it might be impossible for him to see A` and B` at the same time and at different time. I also have no idea if there is any computer simulation that can show so,,, If the external observer wants to know whether A` and B` times are different, he should ask them once the lightning struck A` and B`

Any observer is perfectly entitled to use accepted physics to predict what the clock readings will be for A' and B' when the lightning struck them. The 'external' observer deduces that the clock readings will be different. And when he contacts those observers later, their measurements will confirm that.

 

[Adel Makram]

I would like to say that assuming a non-simultaneous events in a FOR different from that of the observer is based on common-sense logic. But, if the observer wants to be sure, he should have an objective optical evidence or develops a new thought experiment not based on light transmission alone

 

[Adel Makram]

I have found a semi solution to the Doppler paradox. Regarding the interference pattern part, the light from both ends A` and B` has to reach a middle point in the embankment FOR (M) so as to enter into a slit and then double slit before projecting into screen. Now, The train observer sees the external observer moving from B` to A` direction with a velocity = -v. and when the 2 ends at the embankment received the light from A` and B`, he see that the light fro B` which happens first has to travel a longer distance than from A` to reach the middle of the embankment point. And also the accumulated phase change from B` and A` should be compensated when they reach M. SO the net effect on the screen will be black and bright strips which is the same result as the external observer

 

[Adel Makram]

However, because the train observer will see the lights from A` and B` will be received by embankment observer at the ends of the train as different colour, he can ask them directly about the colour of lights they received. Then, he will found a difference between what he sees as a different colour and what the external observer see as same colour and hence the paradox will emerge again because there is no such way to transform the different colour of lights at B` and A` to the same colour at B and A. This time will be a subjective paradox