Revisiting Einstein's Train Experiment: Unraveling the Mysteries of Relativity

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Discussion Overview

The discussion revolves around Einstein's train thought experiment, particularly focusing on the relativity of simultaneity and how observers in different frames perceive the timing of events, such as lightning strikes. Participants explore the implications of special relativity on observations made from a moving train versus a stationary observer.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question how the observer on the train perceives the timing of lightning strikes, suggesting that moving towards one strike should affect the perceived order of events.
  • Others argue that the speed of light remains constant and that velocities cannot simply be added in relativity, leading to different observations of simultaneity based on the observer's frame.
  • There is a discussion about whether the lightning strikes actually occur at different times or if the perception of timing is influenced by the observer's motion.
  • Some participants propose that the events' simultaneity is frame-dependent, emphasizing that different observers may disagree on the timing of events due to their relative motion.
  • A later reply suggests that the concept of simultaneity is not absolute and depends on the reference frame, which leads to confusion among participants regarding the interpretation of observations.
  • Questions arise about the implications of recording events with synchronized clocks on a moving train and how this affects the perceived order of events.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the timing of events as perceived by different observers. There is no consensus on the interpretation of simultaneity or the implications of the train thought experiment.

Contextual Notes

Some participants highlight the need to understand the derivations of Lorentz transformations and the principles of special relativity to grasp the nuances of the discussion. There are unresolved questions about the nature of simultaneity and how it relates to the observer's frame of reference.

  • #61
harrylin said:
One conceptual model that works for SR is that the car and the light travel (or perhaps one should say "propagate") through the same medium. That's one way to make sense of it.
Another conceptual model that works for SR is that the car and the light describe trajectories through Spacetime, interpreted as a 4D physical "medium".
There were never ending debates on this forum in which people, in vain, tried to disprove either or both interpretations, and a stop of such debates is being enforced here. Remains that you can choose the interpretation you like: whichever fits better with how your brain is wired. :cool:
You can find the debates including elaborations of how those models work by means of a search on this forum of such terms as "block universe".

Numbers - speed of object

Light from any moving object will arrive at the observer at C. That observer will calculate the speed of light with relation to the moving object as: C minus speed of object.

Example

Light from a spacecraft heading towards Earth at 0.99c will arrive at Earth at speed C. The speed of the spacecraft is 0.99C. The speed of light is C. Therefore the speed of object with relation to the light emitted is 1C - 0.99C = 0.01C according to observers on Earth

For the comet the speed of light with relation to itself would obviously not be 0.01C, it would be C. The comet would calculate that the light arrived at Earth at 1.99C (from the comets perspective)

The formula for adding velocities is not required for the above analysis. It would be required if the comet traveling towards Earth at 0.99C fired a rocket towards Earth at 0.2C (or any velocity) relative to itself. Then the speed of the rocket relative to Earth would be calculated using the velocity addition formula.

Sources

"Spacetime Physics"

http://galileo.phys.virginia.edu/classes/252/time_dil.html

Interpretation

I don't think the special theory of relativity is matter of "interpretation" - particularly for non experts in the field (like me). What difference does it make how one's brain is "wired"? How is that relevant to the facts? How can physics be a matter of personal choice?

Where you describe a "medium" through which light and the car "propagate", would such a medium be analogous to the ether? How can that be "one way to make sense of" the Theory.

How can you describe Spacetime as "another conceptual model that works for special relativity"?
 
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  • #62
15characters said:
Numbers - speed of object

Light from any moving object will arrive at the observer at C. That observer will calculate the speed of light with relation to the moving object as: C minus speed of object.

Example

Light from a spacecraft heading towards Earth at 0.99c will arrive at Earth at speed C. The speed of the spacecraft is 0.99C. The speed of light is C. Therefore the speed of object with relation to the light emitted is 1C - 0.99C = 0.01C according to observers on Earth

For the comet the speed of light with relation to itself would obviously not be 0.01C, it would be C. The comet would calculate that the light arrived at Earth at 1.99C (from the comets perspective)

The formula for adding velocities is not required for the above analysis. It would be required if the comet traveling towards Earth at 0.99C fired a rocket towards Earth at 0.2C (or any velocity) relative to itself. Then the speed of the rocket relative to Earth would be calculated using the velocity addition formula.

Sources

"Spacetime Physics"

http://galileo.phys.virginia.edu/classes/252/time_dil.html

Interpretation

I don't think the special theory of relativity is matter of "interpretation". Especially if you do not understand the basics - like velocity addition. Can you explain?

For example, where you said a "medium" through which light and the car "propagate", would such a medium be analogous to the ether? How can that be "one way to make sense of" the Special Theory.

How can you say spacetime is just one of the many "conceptual model" that works with relativity and that another model that works would be one where there is a medium through which light passes (similar to ether)?

Finally, what difference does it make how one's brain is "wired"? How is that relevant to the facts? How can it be a matter of personal choice which interpretation is correct?

See our FAQ for how multiple interpretations such as Harrylin mentions are possible, and also the PF policy he refers to:

https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/
 
Last edited by a moderator:
  • #63
Thanks guys for your answers, I have some personal things to do and I don't have time to read through last 7-8 replies but I will. And I will read Spacetime Physics.
 
  • #64
A bunch of unnecessary argumentation has been removed from this thread.

Please try to stay on topic... and not make unnecessary work for the mentors... Please?
 
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  • #66
PAllen said:
See our FAQ for how multiple interpretations such as Harrylin mentions are possible, and also the PF policy he refers to:

https://www.physicsforums.com/threads/what-is-the-pfs-policy-on-lorentz-ether-theory-and-block-universe.772224/

Bad link :(
 
Last edited by a moderator:
  • #67
pervect said:
Bad link :(
Well, so is the link from the FAQ list at the top of relativity forum! This was apparently recently broken. It should be fixed.
 

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