When does a quasiparticle become “particle physics”?
As far as I can tell, protons and neutrons are quark-gluon quasiparticles, but we’re happy to call studying protons and neutrons “particle physics”.
From Wiki:
> complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum
That is, this description fits protons and neutrons relative to quarks and gluons: very cold quark-gluon regions behave as if protons and neutrons exist.
Quasiparticles, as usually defined, are embedded in some bulk substrate. So electron holes exist as part of a chunk of metal, for example. Phonons are mechanical vibrations of some bulk matter. They're not made of any particular piece of the bulk matter, like a molecule is made of atoms or a proton is made of quarks; they're emergent phenomena (an electron hole is "made of" not an electron- it's only a hole because of the matter surrounding it).,
Protons and neutrons, on the other hand, exist in free space. You can accelerate protons and fire them at the moon (or whatever). You can't do that with phonons or electron holes. They are composite particles (not fundamental) but they aren't quasiparticles.
(quarks, weirdly, can't exist in free space. If you try to pull a proton apart you will have to put so much energy into it that you generate more quarks which then immediately couple up with the proton's quarks, possibly in a novel combination producing new composite particles. So you have to study composite particles to study quarks)
I’m unaware of any “free space” which doesn’t have a mass of quarks and gluons oscillating, so I’m not sure I follow. In fact, the mass of the proton arises from disrupting that typical quark-gluon oscillation.
I’m also unsure that’s true, even ignoring that issue:
I can shoot an electron hole by moving the chunk of metal it’s situated in, the same way I can shoot a proton by shooting the constituent quarks and gluons.
You can’t separate an electron hole from the metal, but you also can’t separate the proton from quarks and gluons.
Sure, you can take it further and declare that electrons are actually quasiparticles because they're actually excitations of surrounding fields, if you want. I'm not sure what it gets you though- there are real differences between an electron hole and an electron and that's what the quasi- moniker is getting at.
Sure — but I wasn’t talking about electrons, which as far as we can tell are fundamental particles.
I was talking about protons and neutrons.
What distinguishes a proton, which gains its mass as a hole in the quark-gluon fuzz permeating the universe, from an electron hole in metal?
I think that gets you something:
You can understand protons and neutrons as holes in the “crystallized” space that came out of the universe cooling to its current state — that the fuzz of quarks and gluons is something like a “metal” in which protons and neutrons are “holes”.
It is mathematically useful to think of space as being full of virtual particles including quarks, gluons, and electrons, but there isn't actually a quark-gluon "fuzz" permeating the universe. There was such a physically real fuzz, or more properly a quark-gluon plasma in the extremely early universe (the first few microseconds) which "froze" into hadrons, but this is more akin to water in a cloud condensing into snow.
You can certainly formulate the math such that hadrons, or any other particle for that matter, behave like holes in a substrate, indeed this is the basis of quantum field theory. But unlike quasiparticles where that substrate is something in the universe like a block of metal, for regular particles the substrate is the universe.
I appreciate the time people are taking to walk me through this confusion!
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> You can certainly formulate the math such that hadrons, or any other particle for that matter, behave like holes in a substrate, indeed this is the basis of quantum field theory.
Okay — I’m with you here.
> But unlike quasiparticles where that substrate is something in the universe like a block of metal, for regular particles the substrate is the universe.
Okay — but so what?
Why is it different that it’s within a metal than the stuff the universe cooled into? In both cases, we’re discussing an emergent object with new quantum numbers in some substrate:
- electron holes are a hole in the fuzz of electrons in metals
- protons are a hole in the background fuzz of quarks and gluons in cold aether
> It is mathematically useful to think of space as being full of virtual particles including quarks, gluons, and electrons, but there isn't actually a quark-gluon "fuzz" permeating the universe.
I’m not sure I follow: proton mass is related to flux tubes suppressing that fuzz in the area of the proton.
Empty space has energy, which manifests as that particle fuzz.
> Why is it different that it’s within a metal than the stuff the universe cooled into?
Because that's the point of classification - we want to distinguish between case A and case B. Everything in existence is an emergent property of the universe, but you can't really have any meaningful conversation if the only noun in your vocabulary is "stuff."
> protons are a hole in the background fuzz of quarks and gluons in cold aether
No, there is no cold aether, and protons are not holes in anything. They are composite particles. To the degree that their constituent parts can be described as excitations of quantum fields, so can they, but they are no less real.
> I’m not sure I follow: proton mass is related to flux tubes suppressing that fuzz in the area of the proton. Empty space has energy, which manifests as that particle fuzz.
Proton mass comes from the confinement of its constituent parts. Only about 9% of the proton's mass is a result of the quarks it contains interacting with the quark field, which again is not literally a "fuzz" of discrete particles. Flux tubes are just shapes of magnetic fields. Protons are not just their mass, they have many properties.
> Because that's the point of classification - we want to distinguish between case A and case B.
Right — but why?
What is useful about that classification if the two types of particles emerge the same way, as holes within a substrate?
What do we gain in “composite” vs “quasi”?
> No, there is no cold aether, and protons are not holes in anything.
There is — we can measure vacuum energy as existing. We can also measure spacetime as existing, directly. We know there’s an aether.
> Proton mass comes from the confinement of its constituent parts. […] Flux tubes are just shapes of magnetic fields.
Flux tubes are the region where the connection between quarks suppresses the fuzz from vacuum energy. That’s where the non-quark mass comes from. (As you call it, confinement.)
Hey don't throw shade on quasiparticles, they're people too.