2

An 'free' electron accelerated in an electromagnetic field can both absorb and emit a photon. What about an election accelerating in a gravitational field?

Edit: Some users have suggested that the question is a duplicate. However, my question asks about photon absorption, not radiation of photons.

Abdul Moiz Qureshi
  • 151
  • 2
  • 14

1 Answers1

1

A 'free' electron accelerated in an electromagnetic field can both absorb and emit a photon.

Both electrons and photons belong to the table of elementary particles in the standard model of particle physics, i.e. are quantum mechanical entities and have to be modeled as such. Thus , an electron does not absorb a photon, it interacts with a photon according to the rules of quantum mechanics. Feynman diagrams are used to model the integrations necessary to find the probabilities of interacting electrons and photons, in this case called Compton scattering.

compton scattering

What about an electron accelerating in a gravitational field?

If we accept the effective quantization of gravity, i.e. that gravitons will be part of the future standard model of elementary particles, an analogous diagram will exist, where a graviton will replace one of the photons in the diagrams.

anna v
  • 233,453
  • I think some confusion about "an electron does not absorb a photon" comes about due to the diagrams: where's the photon in the center section? It's certainly looks like it's been absorbed. – Maury Markowitz Nov 08 '18 at 18:20
  • It is not called absorption , as the intermediate line is just a mathematical representation within an integral, integrated over the limits. It is not a real electron as its mass is variable over a continuum of values, and off mass shell. Absorption would mean the mass of the electron would change in its center of mass system, and this is false. – anna v Nov 08 '18 at 18:38
  • That's just it, these diagrams are often put up as an "easy way to understand" these things, but in fact, there is a serious complexity that is not actually illustrated. At first glance, anyone who looks at that sees a missing photon that's "been absorbed". So now you're back to explaining everything you hoped the diagram might avoid! – Maury Markowitz Nov 08 '18 at 18:45
  • @MauryMarkowitz I put up the diagram because it is the quantum mechanical correct model. It is not called absorption, but compton scattering after all. It also allows to see how gravitons would enter in the game. – anna v Nov 08 '18 at 18:50
  • So an electron being accelerated by a gravitational field won't radiate photons? Has an experiment been done to verify this, and can anyone provide a link to such an experiment? – Abdul Moiz Qureshi Nov 09 '18 at 08:38
  • @AbdulMoizQureshi I just described the opposite , in the correct quantum mechanical frame. A graviton on the left interacting with an electron can transfer its energy and a photon appear. That is how acceleration is in he quantum frame. This interaction is very improbabble because the gravitational-electron coupling is very small, so it cannot be measured, see the couplings here http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/funfor.html – anna v Nov 09 '18 at 11:10
  • But has an actual experiment been done to show that an electron accelerating in a gravitational field won't emit or absorb photons? – Abdul Moiz Qureshi Nov 14 '18 at 08:59
  • did you look at the size of the coupling constants in the link I gave above? The electron couples with the electromagnetic field so much more, its radiation within errors fits the electromgnetic calculations, there is no way to discern the effect of the gravitational acceleration that all electrons undergo anyway in the gravitational field of the earth. It will be 10^-37 smaller. there can be no experiment to reach the necessary accuracy. There is a tiny probability to emit due to a graviton interaction, but it is not measureable – anna v Nov 14 '18 at 09:22