Einstein's train thought experiment

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Discussion Overview

The discussion centers around Einstein's train thought experiment, specifically the concept of simultaneity in different frames of reference. Participants explore how the perception of simultaneous events, such as lightning strikes, varies between observers in motion and those at rest, delving into the implications of relativity in this context.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question why the lightning events are defined as simultaneous for Stanley and suggest that they could be simultaneous for Mavis instead, depending on the frame of reference considered.
  • Others clarify that if the lightning strikes are simultaneous in Stanley's frame, then Mavis would perceive them as not simultaneous, highlighting the relativity of simultaneity.
  • One participant acknowledges a misunderstanding regarding the book's explanation, realizing that it referred to simultaneity from Stanley's perspective.
  • There is a challenge regarding the accuracy of the illustrations in the book, with a participant noting an error in the representation of the moving train and observers.
  • Another participant points out that the book implies simultaneity from Stanley's point of view, which they initially overlooked due to the complexity of the text.
  • Questions arise about whether the observers are positioned at the midpoint of the lightning strikes, indicating a need for clarification on this detail in the book.

Areas of Agreement / Disagreement

Participants express differing interpretations of simultaneity based on the frame of reference, indicating that multiple competing views remain. There is no consensus on the specifics of the thought experiment as presented in the book.

Contextual Notes

Participants note limitations in their understanding due to the complexity of the text and the potential inaccuracies in the illustrations provided in the book. The discussion reflects a reliance on specific definitions of simultaneity that may not be universally agreed upon.

Nikitin
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Why did they define the lightning event to be simultaneous for Stanley? Why can't it be simultaneous for Mavis, so that the lighting hits A first?
 
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In that case Stanley would conclude the two lightning strikes were not simultanous in his frame of reference.

As for
so that the lighting hits A first?
, that statement has to have a qualifier of which frame of reference you are referring to - that of either Stanley's or Mavis's or perhaps of another viewer in another inertial frame of reference who might not agree with Mavis or Stanley.
 
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Oh I see now. The book simply said two lightings hit A and B at the same time, but now I understand they obviously were talking from Stanley frame of reference.

I'm still stuck in the Newtonian way of viewing things.

thanks
 
Last edited:
Nikitin said:
The book simply said two lightings hit A and B at the same time...
Where did the book say that? I thought the whole point of the explanation in the book was that at the same time, in other words, simultaneity, "depends on the frame of reference".

[There is an error in the second drawing, (b), where they show the points A' and B' having moved to the right, but they don't show the train and Mavis also moving, like they show in the two drawings below it.]

By the way, this thought problem is similar to the one presented by Einstein in 1920 but there you will see that Einstein specifically states that the lightning strokes "are simultaneous with reference to the railway embankment". He also specifically states that the observer on the train is at the midpoint between the lightning strikes (not necessarily the midpoint of the train).

Does your book go into these details in a part earlier than where you photographed?
 
They mentioned "suppose the wave-fronts reach Stanley simultaneously" which implies simultaneousness from Stanley's POV, so yes they did say it but I missed it in the wall of text, and got confused.
 
Good, did they also say anything about the observers being at the midpoint of the lightning strikes?
 

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