A relativity problem (train & platform)

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Discussion Overview

This discussion revolves around a relativity problem involving a train and a platform, focusing on the differing perspectives of observers in the train's frame and the platform's frame. Participants explore the implications of length contraction, simultaneity, and the nature of events as perceived by different observers in a high-velocity scenario.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant describes a scenario where a train approaches a platform at high speed, leading to length contraction effects that create confusion regarding the events observed by different frames.
  • Another participant questions the apparent asymmetry in the observations of the train and platform, noting that while the train appears to stretch in one frame, it does not seem to pass the platform in another.
  • Some participants propose analogies, such as comparing the situation to a plane landing, to illustrate the effects of perspective and length contraction.
  • Concerns are raised about the relativity of simultaneity, with one participant arguing that the front of the train should either pass the platform or not, suggesting a need for clarity on this point.
  • Another participant asserts that all frames agree that the front of the train passes the platform, emphasizing the importance of understanding how braking occurs at different times in different frames.

Areas of Agreement / Disagreement

Participants express differing views on the implications of simultaneity and length contraction, with no consensus reached on whether the front of the train passes the platform in all frames. The discussion remains unresolved regarding the interpretation of events across different reference frames.

Contextual Notes

Participants highlight the complexities of simultaneity and the effects of high-speed travel on perceptions of distance and time, indicating that assumptions about the nature of events may vary significantly between frames.

  • #31
Farsight said:
Whoa. I'm NOT saying the train ends up 10km long. I'm saying that's not factual, but is an illustration of where the looseness of the thought experiment takes us. And I'm saying that if the train stopped in the middle of the platform the front of the train DID NOT pass the front of the platform.

Don't be rude, MeJennifer.
I am not sure anymore what you are saying :smile:

Does the train pass the end of the platform: YES
Does the train get longer when it decellerates from the perspective of the frame of the platform: YES
Does the train get longer when it is stopped than the length as measured in the train's restframe: NO

Do you agree?
 
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  • #32
Farsight said:
Whoa. I'm NOT saying the train ends up 10km long. I'm saying that's not factual, but is an illustration of where the looseness of the thought experiment takes us. And I'm saying that if the train stopped in the middle of the platform the front of the train DID NOT pass the front of the platform.
If the train does not remain rigid, then the train can elongate, and it definitely will if each part accelerates instantaneously. And if you add something like the Born rigidity condition, the train must accelerate over an extended period, so even if the middle of the train begins to accelerate at the moment it passes the middle of the platform, it may not stop until it has passed the end of the platform.
 
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  • #33
Yes of course I agree MeJennifer. Sorry if I wasn't very clear but please reread my posts. Thank you for that Jesse.
 

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