Einstein's train (simultaneity)

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SUMMARY

The discussion centers on Einstein's train thought experiment, specifically analyzing the simultaneity of light signals emitted from both ends of a moving train car. The observer, moving at speed v relative to the train, perceives both signals simultaneously when positioned at the midpoint of the train. However, the observer's frame of reference leads to a conclusion that one signal is perceived first, challenging the notion of simultaneity. The conversation highlights the complexities of relativistic physics and the implications of relative motion on the perception of time.

PREREQUISITES
  • Understanding of Einstein's theory of relativity
  • Familiarity with the concept of simultaneity in physics
  • Knowledge of reference frames and relative motion
  • Basic principles of light propagation
NEXT STEPS
  • Study Einstein's theory of special relativity in detail
  • Explore the implications of simultaneity in different reference frames
  • Learn about Lorentz transformations and their applications
  • Examine real-world applications of relativistic effects in modern physics
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Physics students, educators, and anyone interested in the foundational concepts of relativity and the nature of time and space in physics.

sunrah
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Homework Statement



We have an observer moving along a moving train car with speed v (assumed to be relative velocity between observer and car). Two light signals are emitted from each end of the car.

a)Where is the observer if he sees both signals simultaneously?
b)From his point of view, which signal was sent first?

Homework Equations


None

The Attempt at a Solution



I simply took the frame in which the observer is at rest and said the train is moving past with speed v. This is the typical Einstein's train scenario with the observer on the platform (except the train is pretty slow). So our observer must be passing the middle of the train when he sees the lights.

But why the second part of the question? So I must be wrong.
 
Last edited:
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sunrah said:

Homework Statement



We have an observer moving along a moving train car with speed v (assumed to be relative velocity between observer and car). Two light signals are emitted from each end of the car.

a)Where is the observer if he sees both signals simultaneously?
b)From his point of view, which signal was sent first?


Homework Equations


None


The Attempt at a Solution



I simply took the frame in which the observer is at rest and said the train is moving past with speed v. This is the typical Einstein's train scenario with the observer on the platform (except the train is pretty slow). So our observer must be passing the middle of the train when he sees the lights.

But why the second part of the question? So I must be wrong.

Have you considered the possibility "neither, they were sent at the same time"
 

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