Einstein's Train Thought Experiment

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Discussion Overview

The discussion revolves around Einstein's train thought experiment, focusing on the nature of simultaneity and the perception of time between different observers. Participants explore the implications of relative motion on the timing of events, questioning whether an absolute timing exists independent of observers.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that events can appear to occur at different times depending on the observer's frame of reference, questioning the existence of absolute event timing.
  • Others argue that while one can trace back light to determine when an event occurred, observers moving relative to one another may not agree on the timing of those events.
  • A participant notes that both observers in the thought experiment could be correct, highlighting the lack of a universal absolute time that all observers would agree upon.
  • Some participants propose that if two events occur at the same location, all observers will agree on their order, provided nothing travels faster than light.
  • There is a discussion about whether the lady inside the train can determine the order of events based on her movement relative to the lightning strikes, and whether the man on the platform has a more valid perspective.
  • One participant challenges the notion of who is "correct" by suggesting that all frames of reference are equally valid, regardless of their motion through space.
  • A later reply critiques a referenced video on the topic, indicating that it has been previously discussed and deemed inadequate, while recommending an alternative video for better understanding.

Areas of Agreement / Disagreement

Participants express multiple competing views on the nature of simultaneity and the validity of different observers' perspectives. The discussion remains unresolved regarding whether an absolute timing of events exists.

Contextual Notes

Limitations include the dependence on definitions of simultaneity and the implications of relative motion on the perception of time. The discussion does not resolve the mathematical or conceptual complexities involved.

  • #31
duri said:
Let me put this way,
1. Observer moving with velocity v and source of signal from the front and rear are stationary from stationary reference. Observer is stationary with his own reference and source of signal is moving at velocity -v. These two are identical. This doesn't talks about speed of signal so invariance of c is not required.
Why do you think the speed of the source is relevant?

Make it simple. Set it up like this: There are giant flash bulbs at each end of the train. Now the source of each flash moves with the train, so the speed of the source is zero with respect to the train observer.

The setup is the same: The bulbs flash at the same time according to the track observer.

Now what?
 
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  • #32
duri said:
2. Simultaneity of the observer in the train breaks because of c+v and c-v in his frame. Here v is the prime variable for break down of simultaneity and not c. If v goes to zero observer will receive the signals simultaneously. Here also c is irrelevant, only condition is c in c+v and c in c-v must be same. Since c+v and c-v is on the same frame. Frame invariant condition is not required for this.
...
Can someone explain which one of these three points are wrong in classical sense. And why frame invariance of speed of light affects required.

#2 is predicted by Newtonian mechanics, but is demonstrably false (google for "Michelson-Morley experiment") and also is not predicted (but not precluded) by the laws of electricity and magnetism (google for "Maxwell's equations", look at the derivation of ##c## there).

You are right about what happens when ##v## goes to zero... But that's going to be true of all theories.
 
  • #33
Nugatory said:
#2 is predicted by Newtonian mechanics, but is demonstrably false (google for "Michelson-Morley experiment")

If I interpret Michelson-Morley experiment in other way. There is no relative motion between source and observer in observer's frame. So, I can't expect changes in fringe pattern what ever angle the table is rotated. Assumption of ether flowing with velocity v is what demonstrated as incorrect.

Take for example ripple in the water. It doesn't matter observer moves or water container moves, as long as water doesn't flows waves would reflect back at same time. Only in case of water flows, wave reflects at different time. Its all about relation between medium and energy moving through the medium. In case of light since there is no medium, relative velocity is not possible to define between wave and medium. Light has to travel at same speed in vacuum. This also given by electromagnetic properties of vacuum.

I got some understanding while replying this. But I got new confusion too, If medium velocity is the key factor (which is not the case for light in vacuum). How inertial frame comes into picture.
 

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