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My impression is that the notion of "virtual particles" is a bit of an outdated concept. There isn't really as much of a physical distinction between "real" an
by antognini 4y ago
My impression is that the notion of "virtual particles" is a bit of an outdated concept. There isn't really as much of a physical distinction between "real" and "virtual" particles as there is sometimes made out to be. All particles are excitations of some underlying field. Generally speaking, these excitations can have some resonance that allows them to persist for long durations. This resonance occurs when the particle is "on the mass shell" in the jargon --- that is, it has a rest mass that is equal (or at least extremely close) to the observed mass of the particle. Excitations that are "off the mass shell" decay exponentially. But these other excitations do have real observable effects. The Casimir effect is the most famous, but they're also responsible for the Lamb shift and Hawking radiation which have also been observed.
- Chabsff 4y agoHawking radiation has been observed? When did that happen?
- antognini 4y agoIt's been observed in sonic black holes, which are mathematical analogs of gravitational black holes in fluids (though to be fair the experiment has been disputed, so the evidence is not absolutely unambiguous): https://www.nature.com/articles/nphys3863.epdf https://www.nature.com/articles/nphys3863.epdf
- Chabsff 4y agoThanks for the clarification. I don't have the background to be confident about this, but aren't the predicates on which Hawking Radiation is based on part of the equivalency framework between sonic and "real" black holes? If so, then while the observation of Hawking radiation in the model is certainly interesting, calling it an observation of Hawking radiation with regards to real black holes sounds like a stretch.
- antognini 4y agoI agree that observations from analog black holes don't rise to the level of definitive proof of the existence of Hawking radiation around gravitational black holes. But what has been observed demonstrates that a system whose behavior is described by the equations that we believe to be correct will exhibit Hawking radiation.
- nimish 4y agoNo, it's a pretty well-defined concept when you stick to its technical definition as an aid in interpreting terms of a perturbation series as Feynman diagrams. > these other excitations do have real observable effects Yeah, that's the major thing: virtual particles explain observable effects in a sort-of intuitive way. But you could (to my knowledge) get the exact same results without involving any virtual particles, via lattice gauge theory. Since you get the same observable results without them, virtual particles, IMO, shouldn't be considered fundamental to any effect, even if they make the explanation a lot easier. Anything involving complicated interactions with relativity like Hawking-Unruh stuff has an even bigger issue since the notion of a particle/vacuum is observer dependent.
- l33tman 4y agoAll post-classical effects in quantum field theory arise from various "corrections" that come from what you could define as virtual particles, whether it's from the perturbative treatment or a numerical lattice gauge calculation. In the latter, you need to (formally) sum over all possible field configurations, the majority of which will contain half-witted weird off-shell "particles" and the entire spectrum between stuff you'd never see as a particle and the classical resonances. It is more clearly visualized in a perturbative expansion, for sure, but it's a bit disingenous I think to argue that there are no virtual particles in a lattice calculation.
- so-and-so 4y agoYeah, the 'Standard model of particle physics' actually states that particles don't exist and there are only fields around.