When an electron travels through a magnetic field, it alters course and by doing so it emits synchrotron radiation.

What we call magnetic field, as I understand it is a mathematical "simplification" of what would happen on average to (macroscopic) charged particles traveling through said field. But on a quantum scale, these events are explained through photon interactions, or virtual photon interactions. So I guess the virtual photons surrounding the electrons inside the magnet, interact with the electron passing by, altering its course. But there is also a "real" photon being emitted from the traveling electron. The synchrotron radiation photon. The magnet itself does not lose energy by altering the course of the electron. What puzzles me is: the electron changes course, by "spontanaous" emission of a synchrotron photon, so there is no net loss or gain of energy in the system, but it is not that spontanaous, because without the magnet present this would be a highly unlikely event. So if no energy is lost by the magnet, but it is still able to influence the electron's probability of emitting a synchrotron photon, what kind of interaction is this. Can we say that in a way,magnets are sort of a quantum probability amplifiers?

  • $\begingroup$ Not sure I could give a full answer, but the reason the magnet doesn't change energy is only because the magnet is much more massive than the charged particle. If you described this reaction as the magnetic field between two moving charged particles of equal mass the effect would be symmetric. $\endgroup$
    – Señor O
    Commented Dec 8, 2022 at 22:25
  • $\begingroup$ Energy is always conserved .... so if photons are being generated then possibly the electron is losing some kinetic energy. Also usually the electron is being accelerated in an E field .... force x distance is energy. $\endgroup$ Commented Dec 8, 2022 at 22:53
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    $\begingroup$ The magnetic field just deflects the electron; simply changing direction does not cause the electron's energy to change. However, an electron undergoing acceleration will emit radiation; the radiation will carry away energy from the electron, causing the electron to lose kinetic energy and slow down. So the magnetic field never does work on the electron. You don't need to invoke virtual photons to explain this. (You can, but if the above points don't make sense then adding virtual photons is just complicating things unnecessarily). $\endgroup$
    – Andrew
    Commented Dec 9, 2022 at 4:27

1 Answer 1


So if no energy is lost by the magnet, but it is still able to influence the electron's probability of emitting a synchrotron photon, what kind of interaction is this.

See if you can find an inconsistency in the following statement.

The electron has kinetic energy and it is a magnetic dipole. This dipole is influenced and aligned by the external magnetic field. And in the process three things happen:

  1. the electron resists the alignment and converts a (very small) part of its kinetic energy into a photon.
  2. the momentum of the photon deflects the electron a little from its path.
  3. the orientation of the dipole to the external magnetic field is disturbed. This process repeats until the electron has exhausted its kinetic energy and comes to a standstill in the centre of a spiral.

The spiral path is therefore in reality a sequence of arcs, similar to the stringing together of tangerine slices.


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