This is more a question about the Higgs field than anything else. If you were to take, for example, a neutrino and send it out into empty space how could you determine that it has a mass in the first place unless it interacts with a particle? And on that level also couldn't one say that it's not possible to determine what we consider to be mass without the evidence of some interaction between particles?


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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – David Z Feb 5 at 23:37

The rest mass of most fundamental particles (possibly not neutrinos) is a property of the quantum field. Specifically it is the Yukawa coupling to the Higgs field. Since the particles described by a quantum field differ only in their momentum, all similar particles have the same rest mass.

So we can be sure that an isolated particle in a vacuum has the same rest mass as one that is in some situation where it is interacting strongly.

Your choice of a neutrino as an example for your question is an awkward one since we don't know how neutrinos get their mass. However there is no reason to suppose that all neutrinos are not equal just as is the case for the other fundamental particles.

  • $\begingroup$ Presumably is it not through spontaneous symmetry-breaking and the Higgs mechanism just like all other particles. Also I'm of the mind set that no such thing as a rest mass exists, I don't believe that any such statement has physical meaning. $\endgroup$ – Sam Cottle Feb 5 at 17:29
  • $\begingroup$ The neutrino could get its mass through a seesaw mechanism. $\endgroup$ – John Rennie Feb 5 at 17:31
  • $\begingroup$ @SamCottle Only the W and Z bosons (and the Higgs boson itself) get their mass through spontaneous symmetry breaking. Quarks and non-neutrino leptons get their mass through a Yukawa coupling to the Higgs boson. For photons, gluons, and neutrinos, such a coupling does not exist. $\endgroup$ – probably_someone Feb 5 at 17:34
  • $\begingroup$ The implication here is that the Higgs mechanism is stilted and incomplete, also this question was more about how we define mass in the first place. $\endgroup$ – Sam Cottle Feb 5 at 17:55
  • 2
    $\begingroup$ @SamCottle Rest mass is a quantity appearing in the Lagrangian for the field. For the fermions it arises from a Yukawa coupling between the fermion field and the Yukawa field. This definition of rest mass has the advantage of matching experiment. You may have your own definition of rest mass, but unless it can do a better job than the accepted definition you are unlikely to make friends and influence people with it. $\endgroup$ – John Rennie Feb 5 at 18:04

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