Mystery of Einstein's Relativity Solved with Classical Physics

[vin300]

https://curiosity.com/topics/a-mystery-of-einsteins-relativity-has-been-explained-using-classical-physics-curiosity?utm_source=androidapp
If anybody understands what the author is trying to say, kindly elaborate. I haven't read the paper

 

[fresh_42]

The article in question: (PRL - 5 pages)
https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.118.053601

We show how a simple calculation leads to the surprising result that an excited two-level atom moving through a vacuum sees a tiny friction force of first order in v=c. At first sight this seems to be in obvious contradiction to other calculations showing that the interaction with the vacuum does not change the velocity of an atom. It is even more surprising that this change in the atom’s momentum turns out to be a necessary result of energy and momentum conservation in special relativity.

Follow-up article by the authors: (Journal of Modern Optics - html)
http://dx.doi.org/10.1080/09500340.2017.1374482

 

[PeterDonis]

If anybody understands what the author is trying to say, kindly elaborate

Ignore the pop science article; as so often happens, it doesn't give a good description of what the paper actually says.

What the paper actually says can be described as follows:

(1) Consider an atom in an excited state that emits two photons of equal energy in opposite directions. Since the two photons carry equal but opposite momenta, their recoils on the atom cancel and the atom's state of motion should not change.

(2) If we analyze this process in the initial rest frame of the atom, we find that, indeed, the atom's state of motion does not change; it remains at rest, and simply loses energy, and therefore mass (here and hereafter, "mass" means "rest mass" or "invariant mass"), equal to the energy carried away by the emitted photons.

(3) If we analyze this process in a frame in which the atom is moving, we find what appears to be a "paradox": the momentum of the atom changes (whereas in its rest frame it didn't--it remained zero). However, a more careful analysis shows that this momentum change is entirely due to the change in the mass of the atom; its velocity does not change. So there is no actual inconsistency with the principle of relativity; it is just that you have to be careful when analyzing scenarios where the rest masses of objects change.

 

[vin300]

What is recoil shift? Does it affect doppler shift?