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Not really. The "roiling sea of particles" is a metaphor for perturbation series, which very specifically does not work for the strong force at low energies. T
by nimish 4y ago
Not really. The "roiling sea of particles" is a metaphor for perturbation series, which very specifically does not work for the strong force at low energies.
Take anything involving virtual particles as just that, virtual. They're an aid for computation and cannot be observed directly. They aren't necessary either; lattice gauge theory is always applicable if not practical.
The mass(-energy) being from the strong interactions is still true. And the residual bit of the strong force between protons and neutrons works with the virtual particle/perturbation theory approach pretty well, using pions.
- tines 4y agoI'm glad you brought this up, because I've been reading some stuff lately that makes it seem like virtual particles actually have visible effects, like this one: https://www.forbes.com/sites/startswithabang/2019/07/12/yes-virtual-particles-can-have-real-observable-effects/ https://www.forbes.com/sites/startswithabang/2019/07/12/yes-... So is it that these articles are wrong, or that I'm reading them wrong, or that the idea that virtual particles are just for calculations is outdated?
- tadfisher 4y agoWe discovered the mesons by photographing their tracks on plates exposed to the sky. They're real, just extremely short-lived.
- marcosdumay 4y agoWhat a bad piece of journalism, intent on confusing instead of explaining. Virtual particles were invented because they have measurable effects. Physicists don't go around inventing invisible things for no reason. What they are not is "particles". The particle facade is only there because it fits the math. (The article seems to be describing an experiment that measured energy-time uncertainty.)
- cwillu 4y agoIncomplete analogy that's probably a better starting point: if the tone of a bell is a particle, then the other movements of the bell that don't resonate are virtual particles. Now, imagine we called the thermal motions of that bell “virtual tones”, and you have an idea why physicists always sigh and emphasize that virtual. particles. are. not. particles.
- nine_k 4y agoIf virtual particles "fit the math" the same as real particles, what makes them not real? What do they not fit?
- evanb 4y agoWhat makes particles travel long distances as lumps is that they are on-shell. Virtual particles are not on shell. https://en.wikipedia.org/wiki/On_shell_and_off_shell https://en.wikipedia.org/wiki/On_shell_and_off_shell
- nimish 4y agoYou don't _need_ them, and IIRC _can't_ (in general) use them if you deal with non-perturbative effects, unless you do stuff like re-summing infinite series of diagrams and that really makes interpreting the ultimately observable effect in terms of virtual particles interacting difficult.
- burnished 4y agoAn example that comes up in semiconductor is the 'hole' virtual particle. It is the absence of an electron. It is not a real and independent phenomenon. But you can treat it like a particle just fine
- gizmo686 4y agoElectron holes are quasi particles, not virtual particles.
- burnished 4y agoAh hell, guess I have to start treating the stuff I learned in undergrad into the unreliable narrator category. Thanks for the correction!
- cwillu 4y agoVirtual particles are not particles. Virtual particles are all the disturbances in a field that don't behave like particles do. It's really a terrible name to have entered the lay vocabulary: “virtual memory is something that behaves largely like real memory” is _exactly_ wrong, it's more like “virtual memory is all the circuitry that doesn't perform any memory function, but is still made of silicon”.
- antognini 4y agoMy 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.