Do the Energy-Momentum Transformations apply to Photons?

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Discussion Overview

The discussion centers around whether the Energy-Momentum transformations apply exactly to photons, particularly in the context of special relativity. Participants explore the implications of these transformations for photons, including the need for corrective terms and the relationship between energy, momentum, and the speed of light in various frames of reference.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the Energy-Momentum transformations must apply to all entities, including photons, due to the invariant nature of the energy-momentum four-vector.
  • Others question whether corrective terms are necessary when applying these transformations to photons, suggesting that the transformations should hold without modifications.
  • There is a discussion about the role of the relativistic Doppler factor in determining the energy and momentum of photons as observed from different frames.
  • Some participants argue that since photons do not have a rest frame, the Lorentz transformations and derived energy-momentum transformations do not apply to them.
  • Counterarguments suggest that the transformations can still be valid for photons when considering different inertial frames, similar to how one would analyze the momentum of a ball thrown on a moving train.
  • Participants express uncertainty about the implications of the Lorentz transformations when applied to light, particularly regarding the undefined nature of γ when v=c.
  • Some participants propose checking the transformations by plugging in the energy-momentum relationship into the transformation equations to verify consistency.

Areas of Agreement / Disagreement

There is no consensus among participants. Some believe that the Energy-Momentum transformations apply to photons without corrective terms, while others argue that the lack of a rest frame for photons complicates their application. The discussion remains unresolved with competing views on the applicability of these transformations.

Contextual Notes

Participants express various assumptions about the nature of photons, the role of reference frames, and the implications of the Lorentz transformations. There are unresolved questions regarding the dependence of wavelength on the speed of the source and the implications of using the transformations for massless particles.

  • #31
sweet springs said:
In these strict sense rest frame could be applicable for a few kind of single elementary particles
Which is precisely why the term "center of momentum frame" is so common in the particle physics literature.

This convention is not universally used, but it is more descriptive and is appealing to many scientists.
 
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  • #32
Indeed the term "center of momentum frame" is the most precise expression for "rest frame", if not the only correct one at all, of a composite system.
 
  • #33
sweet springs said:
The theory of relativity excludes rigid bodies.

More precisely, it excludes bodies in which internal forces are propagated faster than light. But it is perfectly possible to have rigid motions of bodies, under appropriate conditions.
 

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