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Does the train example show relative simultaneity?


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You have a lot of nerve accusing someone of selective quoting without having even looked at the source. I think that you owe me an apology.


I didn't say I hadn't looked at the source. I said I wasn't going to go and find an online copy to find the context you are misquoting from. Oddly enough, I haven't perfectly memorised the text for 40 years.



And who better to learn SR from than the originator?


Plenty of people. I have read many better explanations.



I further resent being labeled close-minded this early in the game. See my last post for this "session."


A conclusion based on the evidence. Which you have only gone on to reinforce.



Maybe you would like to argue with Tom?


I don't know who "Tom" is. But he seems to agree that coordinates are arbitrary and therefore you cannot have an absolute frame of reference. And therefore you are wrong.


Feel free to open your mind and read the bits of Einstein's text you appear to have skipped over.

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  • 5 weeks later...

Getting back to the initial posts, I will go out on a limb and say that yknot is not nuts.


There are three events: (1) emission of light, (2) light striking O1, and (3) light striking O2. The light emission and the light strikes are all events, and serious physicists would agree. Witness Taylor and Wheeler, Spacetime Physics, page 10: "Another event is the emission of a flash of light from an atom . . . A fourth event . . . is the strike of a lightning bolt on the rudder of an airplane." See also the (less august) wikipedia entry on "Spacetime": "Events which occur to . . . a photon along its path (i.e., while traveling at c, the speed of light), all have light-like separations." yknot correctly described the events that occur to the photons (striking the observers) as events, and correctly described them as being light-like events (perhaps better to say, like wikipedia, that they have light-like separation).


Also, it is not necessary to have a second light source to show the relativity of simultaneity (although Einstein uses one in the train example, and admittedly yknot is using the train example). All you need is a light source that flashes spherically outward. Then, when the light strikes observers who are equidistant and on opposite sides of the light source in its frame, the strikes will be simultaneous in the light source's frame. But they will not be simultaneous in other frames that are in motion relative to that frame. See Spacetime Physics at page 176.


yknot, in your original post you say that the two strikes are absolutely in the order O1 first and O2 second because they are light-like. But it is not the case that all events that have light-like separation occur the same order in all inertial reference frames, as Taylor and Wheeler show. I agree with the early responses that the relative motion is important, and that it is fundamentally what special relativity is all about. If you use a second light source on the opposite side of the observers, or if you separate the two observers slightly at inception and put the light source between them, there will still be differences in how the observers observe the light (just as you point out in your original post), but as the other posters say this just illustrates special relativity. It is not inconsistent with SR.

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