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

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The discussion centers on Einstein's train thought experiment, exploring the relativity of simultaneity. Observers on the train perceive lightning strikes at different times due to their motion, while an external observer sees them as simultaneous. The confusion arises from misunderstanding how light travels and the concept of absolute time, which does not exist in relativity. The conversation emphasizes that events can appear simultaneous in one frame but not in another, highlighting the importance of reference frames in understanding relativity. Ultimately, the relativity of simultaneity is a fundamental aspect of how different observers perceive events based on their relative motion.
  • #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 "propogate", 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 "propogate", 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/
 
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  • #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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