Can an electron in a magnetic field radiate a virtual photon?

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Discussion Overview

The discussion revolves around the nature of photons emitted by electrons in a magnetic field, particularly in relation to virtual photons and their connection to phenomena like MRI and Zeeman transitions. Participants explore the distinction between real and virtual photons in the context of quantum mechanics and magnetic resonance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant references Leonard Susskind's description of an electron radiating a photon when transitioning between spin states in a magnetic field, questioning if this photon is a virtual photon related to electromagnetic mediation.
  • Another participant clarifies that the photons involved in magnetic resonance are real photons of low energy, specifically in the context of MRI, which primarily involves protons rather than electrons.
  • A third participant explains that virtual photons are not emitted as real photons and are represented as internal lines in Feynman diagrams, suggesting that they cannot be directly radiated.
  • A later reply emphasizes that the photon emitted from an electron's spin flip is a real photon, observable as electromagnetic waves, and cites the 21 cm line of hydrogen as a significant example.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the photons involved in the discussed processes, with some asserting that virtual photons cannot be emitted while others focus on the real photons associated with magnetic resonance. The discussion remains unresolved regarding the relationship between virtual photons and the phenomena described.

Contextual Notes

Participants highlight the distinction between real and virtual photons, with some assumptions about the applicability of quantum mechanics to classical phenomena like MRI. The discussion does not resolve the complexities of these concepts.

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TL;DR
Does a spin in a magnetic field radiate a virtual photon?
In Theoretical Minimum: Quantum mechanics, Leonard Susskind describes an electron in the higher energy spin state in a magnetic field radiates a photon of energy ##\hbarγ|B_0|## and flips into the lower energy spin state. I am wondering if this photon is related to the "virutal photon" that mediates the electromagnetic field. I am wondering whether a large number of such a photon relates the Zeeman transition of the spin 1/2 particles to a classically observable magnetic field, such as MRI? I am sorry if my question is not clear, I do not have a strong background in physics yet. A thoughtful explanation including equations would be greatly appreciated. Thank you.
 
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The quantum description of absorbing energy by atoms (or electrons) for magnetic resonance involves actual (not virtual) photons of low energy (i.e. radio frequencies). The MRI uses the transitions of protons in the hydrogen nucleus and so while similar to the electron Zeeman splitting, it is not usually called that.
Most of the details of magnetic resonance are completely understandable in terms of Classical physics although the Quantum explanation is sometimes easier to understand.

There are many articles extant without me reproducing them here.
 
The photon emitted due to a spin flip of an electron within an atom with the energy difference between the two possible spin orientations due to the magnetic field of nucleus, i.e., the hyperfine structure of the atomic energy levels, is of course a real photon. It can be observed as em. waves. The most important example for astrophysicists is the 21 cm (wavelength) line of the hydrogen atom:

https://en.wikipedia.org/wiki/Hydrogen_line
 

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