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When an electron drops to a lower orbit, energy is released as a photon. Gluons expand and contract in-between quarks, described like springs or rubber bands that have tremendous force when extended but only minor force when contracted. Where does that energy go when a gluon contracts? Is it released as some other virtual particle?

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  • $\begingroup$ Like all other “elementary” particles in the Standard Model, gluons — the quanta of the gluon field — are point particles and can’t expand or contract. The gluon field forms, in some sense, a color flux tube and this flux tube can expand or contract. Since the gluon field only interacts with itself and quarks, any energy transfer has to be with those fields. $\endgroup$
    – Ghoster
    Commented Nov 6, 2022 at 21:15

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In quantum mechanics, a proton is a stationary state, like the ground state of a hydrogen atom: all protons are indistinguishable at all times, forever. The only time evolution is an unobservable phase factor.

Any language that contradicts that (other than GUTs and proton decay) is metaphorical: don't take it too seriously.

An analogy of atomic transitions is the decay of the Delta baryon:

enter image description here

While gluons are working underneath, this can be viewed in effective field theory as an energy level transition via pion emission.

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  • $\begingroup$ I have read many times that electrons are indistinguishable but I have never heard the same for protons. Given that protons contain "a sea of quarks and gluons popping in and out of existence" I can't see how they can be indistinguishable from each other or even individually given that they are constantly changing. Can you give me more information on this aspect of your answer? $\endgroup$
    – foolishmuse
    Commented Nov 7, 2022 at 0:44
  • $\begingroup$ @foolishmuse They aren't constantly changing. That language is not precise. Atoms in BECs are certainly indistinguishable, yet the lamb shift tells us $e^+e^-$ pairs are "popping in and out of existence" from the virtual photon that binds the electron and nucleus. It's just an expression left over from old fashion perturbation theory. $\endgroup$
    – JEB
    Commented Nov 8, 2022 at 14:27

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