Light clock running faster than light?

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Discussion Overview

The discussion revolves around the Twin Paradox, specifically focusing on the behavior of a light clock as perceived by an observer in a non-inertial frame during the journey to a distant star and back. Participants explore the implications of simultaneity shifts and the relativistic Doppler effect on the perceived speed of light and the operation of the light clock.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes observing their twin's light clock running slow during the outbound journey and then running fast upon turning around, questioning whether this is due to the light ray bouncing faster than light or the clock contracting.
  • Another participant notes that the interpretation of observations depends on the mathematical details of the non-inertial frame used, suggesting that using radar coordinates maintains the speed of light at ##c## without sudden jumps in simultaneity.
  • A different participant emphasizes that length contraction is relevant only between inertial frames and that the computation of what is seen is complex and frame-dependent.
  • One participant argues that the simultaneity shift is a convention and does not represent a physical change in the twin's clock, asserting that it does not affect the physics involved.
  • Another participant states that the observed changes in the twin's clock are linked to the relativistic Doppler effect, which is invariant regardless of coordinate choices, and advises looking into the mathematics of this effect.
  • Participants collectively reject the notion that the light ray could bounce faster than light, reinforcing the need to consider the relativistic Doppler effect in their observations.

Areas of Agreement / Disagreement

Participants express differing views on the implications of simultaneity shifts and the interpretation of observations in non-inertial frames. There is no consensus on how to reconcile these observations with the principles of relativity, indicating ongoing debate and exploration of the topic.

Contextual Notes

Participants highlight the complexity of interpreting observations in non-inertial frames and the dependence on chosen coordinate systems, which may lead to different conclusions about the behavior of the light clock.

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TL;DR
Twin Paradox - Light clock speed up?
Twin Paradox.

I am on the outgoing rocket and look back at my stay at home twins light clock (two mirrors with a ray of light bouncing in between)

I get to the nearest star and on the outbound journey my twins clock apears to run slow.

When I turn around my plane of simultaneity shift and I see my twins clock run fast as I “catch up” to in respect to his plane of reference for the return trip.

Do I see the light-ray of his clock bouncing faster than the speed of light between the mirrors or do I see his clock contract so that the light-ray can bounce quicker in the shorter space?


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tagehedin said:
TL;DR Summary: Twin Paradox - Light clock speed up?

Do I see the light-ray of his clock bouncing faster than the speed of light between the mirrors or do I see his clock contract so that the light-ray can bounce quicker in the shorter space?
It depends on the mathematical details of your non-inertial frame. Which you did not specify.

If you use something like radar coordinates (my preference) then the speed of light is always ##c## and there is no sudden jump in simultaneity
 
Last edited:
Length contraction is a phenomenon between inertial frames, and you aren't using one. What you actually see is messy to compute; how you interpret it depends on your choice of non-inertial frame.
 
tagehedin said:
When I turn around my plane of simultaneity shift and I see my twins clock run fast as I “catch up” to in respect to his plane of reference for the return trip.
A simultaneity shift, as you call it, is just a change of simultaneity convention. Nothing physical happens to your twin's clock. It's not a physical change to anything.
 
tagehedin said:
When I turn around my plane of simultaneity shift and I see my twins clock run fast
These two things have nothing to do with each other.

The "simultaneity shift" is purely a convention that depends on how you choose your coordinates. No physics depends on it.

What you actually see of the other twin's clock is an invariant, independent of how you choose your coordinates: it is the result of the relativistic Doppler effect. When you turn around, you change the relativistic Doppler effect that you observe in the light signals reaching you from the stay-at-home twin.

More here:

https://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_doppler.html

tagehedin said:
Do I see the light-ray of his clock bouncing faster than the speed of light between the mirrors or do I see his clock contract so that the light-ray can bounce quicker in the shorter space?
No.

I suggest looking at the actual math of the relativistic Doppler effect.
 
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