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For the following thought experiment, How to do calculation in relativity of simultaneity

Why is simultaneity considered as an act of seeing the bolts? Even for the passenger in the train, can we not argure that the event may actually be simultaneous for him as well, just that he perceived (with eyes) at a later point of time?

Instead of person in the middle of train doing the observation, I have an observer at each end of the train who just note the time of nearest bolt and tally them later. How do you think this changes things for the given experiment?

How is this thought experiment justified for explaining relativity of simultaneity as it's based on human senses ? Even with Galilean transformation wouldn't this experiment be still valid? Can we reformulate this thought experiment to not have human perception for measurement and still validate the relativity of simultaneity?

FUD
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  • How could the person "observe" something they so not have data for? If you mean that it is a delayed realization then perhaps, but it has to be the same for all observers to be a law or result of physics. –  Dec 27 '18 at 11:53
  • Can't the observation be based on something like a light beam reacting on some.light sensitive plates with a timestamp, which later be taillied by both observers? I am not sure how this experiment establishes perception as basis of non simultaneity. – FUD Dec 27 '18 at 11:56
  • That is exactly correct but does not undo relative simultaneity, as you have suggested.. –  Dec 27 '18 at 12:02
  • IMHO a reading of first chapter of Bernard Shutz's intro to GR will best explain this to you. I can reproduce his core argument here but it will take too much space. The key is to take the human element and the perception stuff away from the experiment. Just think of the observer as a coordinate system and recordings as always made at the point where the event happens. He uses this construction to simply illustrate the failure of simulatenity and then goes on to derive the Lorentz transformation from it. – Apoorv Dec 27 '18 at 12:30
  • Are you saying there is this exact same argument and thought experiment in the book you mentioned? – FUD Dec 27 '18 at 12:34
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    Sorry got too excited I understand this is an answer to my last question. I will take a look at it . Thanks – FUD Dec 27 '18 at 12:37
  • The two observers at the ends of the train, are they on the train and moving with it, or are they standing still on the ground? – md2perpe Dec 27 '18 at 16:46
  • @md2perpe on the train moving with it. – FUD Jan 02 '19 at 09:25
  • In what way do you think that the results of the thought experiment would change with one man standing at each end of the train? – md2perpe Jan 02 '19 at 10:21
  • @md2perpe I felt the space here was too small to express, Please check my comment https://pastebin.com/raw/NQYS14rt – FUD Jan 03 '19 at 13:15
  • The two men will each see their respective bolt without delay, but then they will have to tally their times. How will this be done? – md2perpe Jan 03 '19 at 14:08
  • @md2perpe They just meet each other and show their noted times. – FUD Jan 03 '19 at 17:06
  • @FUD. That's meaningless unless they first have synchronized their clocks. So I suppose that they first have done that in some way. How did they do that? And what conclusion will you draw when their noted times differ? – md2perpe Jan 03 '19 at 17:11
  • @md2perpe They could have tallied the clocks before the train started. – FUD Jan 04 '19 at 06:25
  • @FUD. What makes you think that they will note the same time of the bolts? – md2perpe Jan 04 '19 at 07:24
  • @md2perpe because they are closest to the respective bolts, and light does not have to travel to middle of the train (as per the argument in the Einstein's article). – FUD Jan 07 '19 at 07:50
  • @FUD. According to the man on the ground the two men on the train will see the bolts at the same time, but will they really do it according to their own clocks? – md2perpe Jan 07 '19 at 09:18
  • @md2perpe what do you mean? They have a simple task to stop the watch when they see bolt. – FUD Jan 09 '19 at 09:22
  • @FUD. Yes, but their clocks will not show the same time when they see the bolts. (According to special relativity and the Lorentz transformation.) – md2perpe Jan 13 '19 at 19:40

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Your last statements sort of undo all of modern physics.

  1. A person cannot perceive something that is not there. That is not objective reality. And that is one of the corner stones of all modern physics that we cannot remove ourselves from the basic theory. Observation is required for objective results to be discussed.

  2. Einstein actually considered the fact (as was known at the time) that our senses are electromagnetic. That is that all we are able to observe using our senses is due solely to the electromagnetic force. If there is a symmetry or constraint in EM theory then there is a symmetry and constraint in all observation and knowledge. He writes about this in Meaning of Relativity.

  3. Even if there are deviations in observed simultaneity due to variations in nerve conductivity or delayed perception the observer can be replaced with detectors and what we know from relativity holds for the response of the detectors. So that is on sound and solid ground.

  4. Even is you could devise a theory that had things occurring simultaneously in all frames but perceived differently by different observers all you would have done is move a problem to a different spot under the carpet. Science is based on empiricism. They only thing we seek to describe is when we experience. So building layers of reality that are manifestly non-existent does not serve any purpose.

  • Instead of person in the middle of train doing the observation, I have an observer at each end of the train who just note the time of nearest bolt and tally them later. How do you think this changes things for the given experiment? – FUD Dec 27 '18 at 12:05
  • I have edited my question to make more clear what I meant by human senses. For a person in the middle of the train and person at the ends the perception would be different. – FUD Dec 27 '18 at 12:14
  • It doesn't because they know nothing of each others observation until they meet and compare notes. If they are in the same frame of reference, and synchronized then when they meet in the middle they will see different times recorded and measure they same time delay between observations. They could be two synchronized detectors. –  Dec 27 '18 at 12:14
  • Could you explain why there would be a time difference as there is no distance for the light bolts to travel at each end. Both should see and record bolts at the same time t in the trains frame of reference. – FUD Dec 27 '18 at 12:17
  • It's the movement of the train that causes the time delay. The train is moving, right? If not then relativity states that the events are simultaneous. –  Dec 27 '18 at 12:22
  • According to the thought experiment , the person in the train see one light bolt earlier because he is hasting towards the light beam at one end and away from the other. This is what Einstein has mentioned in book "Relativity The Special and General Theory" in the chapter "The Relativity of Simultaneity". I am just placing a person at each end now. – FUD Dec 27 '18 at 12:28
  • I think you are confusing how the placement comes into the picture. It doesn't matter where a person is placed. It is the movement that causes the delay. Each person will see both bolts and each will measure the same delta t. If you want to shield each person from one of the bolts then my previous statement holds. It seems that you are trying to redefine the events that are being compared. SR does not attempt to compare the time of arrival of bolt 1 at end 1 and bolt 2 at end 2. That is NOT the comparison in the thought experiment. –  Dec 27 '18 at 12:43