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The HN title is incorrect -- perhaps the first direct evidence is Compton's original work, showing that electrons scatter photons. If electrons scatter photons, then photons scatter electrons.

Every time a photon scatters off an electron, there exists a reference frame in which the electron is brought to rest.

I'm certain that one could find an earlier argument than Compton scattering, too. Maxwell surely would have agreed that light could exert force upon charges.

The experiment to which the HN title links, however, is awesome, and is perhaps the first time one has demonstrated stopping 0.5 GeV electrons in a wall of light.




OK we've taken "first" out above.


Genuine question out of curiosity, what is your line of work? I don't see a lot of physicists around here


Physicist.


> If electrons scatter photons, then photons scatter electrons.

Does it mean that photons are able to scatter photons?


Photon photon scattering is a thing [1] but I am not sure whether that is implied by the interaction of light and electrical charged particles acting both ways. I slightly tend to think that is not implied but I am not a physicist.

[1] https://en.wikipedia.org/wiki/Two-photon_physics


Interesting! Thanks


Yes, they are. They cannot interact directly, but they can via "virtual" electron/positron pairs (or actually any other pair of charged elementary particle + antiparticle).


To expand a little -- the process is known as light-by-light scattering.

Searching will turn up plenty of good references, like this one: https://home.cern/about/updates/2017/08/atlas-observes-direc...


What’s the difference between this and radiation pressure on charges (which is classical physics)?


Good question! In radiation pressure the fact that the charges radiate energy isn’t included, it’s just the change in momentum due to to radiation being absorbed or reflected that produces a force. In radiation reaction the charges are accelerated and decelerated by the electric field of the light. Classical electrodynamics says the electrons must give off em radiation, and so must lose energy in the process, so must be an additional force associated with this emission. Physicists such as Dirac looked at classical radiation reaction in the early 20th century, but I don’t think it’s effect has been observed in the interaction of electrons with light before. At very high electron energies and/or laser intensities the classical description of radiation reaction should break down.




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