Redshift of a light pulse between 2 accelerating rockets

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    Light Pulse Redshift
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Discussion Overview

The discussion revolves around the redshift of a light pulse emitted between two accelerating rockets. Participants explore the implications of the rockets' acceleration on the perceived travel time of the light pulse, considering both theoretical approximations and the effects of relative motion.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions the assumption that the light pulse takes a time of ##z/c## to reach the leading rocket, suggesting that the pulse must cover a greater distance due to the forward movement of the leading rocket during that time.
  • Another participant agrees that the initial assumption is a first-order approximation, indicating that the actual scenario may require a more nuanced analysis.
  • A further elaboration is made regarding the displacement of the leading rocket, with a participant proposing a relationship involving the distance covered by the leading rocket during the time the light pulse travels.
  • Another participant confirms the previous points, noting that the reference frame is typically chosen such that the initial velocity of the leading rocket is zero, which leads to the displacement due to acceleration being considered a second-order effect.

Areas of Agreement / Disagreement

Participants generally agree that the initial approximation of the light pulse's travel time is simplistic and that a more detailed analysis is warranted. However, the discussion remains unresolved regarding the exact implications of the rockets' acceleration on the light pulse's travel distance and time.

Contextual Notes

Participants acknowledge that the analysis relies on certain approximations, such as neglecting higher-order terms in the equations of motion and the choice of reference frame. These factors may limit the accuracy of the conclusions drawn from the discussion.

sphyrch
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I'm reading book from here. Suppose two rockets are accelerating with the same acceleration ##a## and are separated by some distance ##z##. At time ##t_0## the trailing rocket emits a light pulse. The book tells that pulse reaches leading box after time ##z/c## as seen in background frame. But won't the pulse actually have to cover a distance more than ##z## to reach the front rocket since the front rocket would've moved forward in that time? This on pg 65
 
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Yes, that is a first order approximation.
 
Dale said:
Yes, that is a first order approximation.
It like this? If front ship moved extra ##x## dist by the time (say ##t##) light reached, then ##ct-z=ut+at^2/2##. and then we say ##u<<c## so we ignore, and we say that time taken is super short so we ignore ##t^2## too. So every thing gets ignored and we get ##ct-z=0##. This the author logic?
 
More or less, yes. The only other thing is that usually they choose the reference frame where ##u=0##. So the displacement due to acceleration is 2nd order (##at^2/2##)
 
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