Lorentz Transforms: Question About Inverting LT Frames

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Discussion Overview

The discussion revolves around the application and inversion of Lorentz transformations (LT) between different inertial frames in the context of special relativity. Participants explore the implications of transforming between frames and the correct method for calculating relative velocities.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant constructs a Lorentz transformation from an un-prime frame to a prime frame and then to a double prime frame, questioning why inverting the first transformation does not yield the same result as a direct transformation between the double and single prime frames.
  • Another participant points out that the relative velocity between frames is not simply the difference of the velocities used in the transformations, suggesting a need for clarification on the addition of velocities in special relativity.
  • A later reply acknowledges the need to apply the special relativity (SRT) addition of velocities to correctly determine the relative velocity between the prime and double prime frames.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial misunderstanding regarding the relative velocities, but there is agreement on the necessity of using the SRT addition of velocities for accurate calculations.

Contextual Notes

The discussion highlights potential limitations in understanding the transformation process and the assumptions regarding relative velocities between frames, which may depend on the definitions and context of the transformations applied.

exmarine
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If I construct a LT from an un-prime frame to a prime fame: S':=LT(S,v') and another to a double prime system: S":=LT(S,v"), then invert the first: S:=LT(S',-v') and substitute it into the second: S":=LT([LT(S',-v')],v"), I do NOT get the same transform as going directly between the double and single prime frames: LT([LT(S',-v')],v") ≠LT(S',[v"-v']). Does this question make any sense? What am I missing?

Thanks.
 
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When going from S' to S'', what velocity did you use?

Realize that if v' is the relative velocity of S and S' and v'' is the relative velocity of S and S'', then the relative velocity of S' and S'' is not simply v'' - v'.
 
Last edited:
Oh? I thought it would be v"-v'. What is it then?

Thanks.
 
Ok, I get it. I have to use the SRT addition of velocities. Thanks!
 
exmarine said:
Ok, I get it. I have to use the SRT addition of velocities.
Right!
 

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