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How Many Elementary Particles Are There, Really?

quantamagazine.org

71–80 of 160 posts

Re: How Many Elementary Particles Are There, Really?

#71
post #62

Physicist here. I don’t buy some of these distinctions, like the chirality. Chirality is an observable, it’s like saying there are two photons because they can come in two polarizations, but polarization is not an inherent property: it depends on how we measure it. So I could describe any photon in the left/right chiral basis just as well as in the vertical/horizontal basis or any two antipodal points in the Poincaré…

Chirality is a real property of (most) elementary particles. For example the electron with left chirality has a weak hypercharge of -1, but the electron with right chirality has a weak hypercharge of 0. https://en.wikipedia.org/wiki/Weak_hypercharge#Definition In some sense, they are very different particles. Also, only the left version interact with the weak interaction.

Re: How Many Elementary Particles Are There, Really?

#72
post #8

Earlier quoted context omitted.

> They're manifestations of fields. Or wave. Everything is a quantum wave. https://www.vlatkovedral.com/everything-in-the-universe-is-a...

A wave is already what we call a manifestation of a field, maybe I skimmed too quickly but I don't get the author's breakthrough point.

I am not sure there’s any breakthrough here, but this article is about a different QM interpretation (as opposed to Copenhagen or Many Worlds). Interesting but seems irrelevant to the discussion here of particles and fields.

Re: How Many Elementary Particles Are There, Really?

#73
post #20

Earlier quoted context omitted.

> if you're looking for the short list of simplest things, the number of types of fields there are is probably what you're looking for Definitely. It's rather strange that the OP article doesn't even mention the word "field". It seems that people in general have a hard time letting go of the idea of particles as fundamental. A good overview of this is "There are no particles, there are only fields" ( https://arxiv.or…

You've said that "37 fields" at least twice. It doesn't seem to come from the arxiv article you linked, though. And it seems rather high to me. (Of course, 118 seems ridiculously high...) Anyway: Would you list them? Or supply a link to somewhere that does?

First, just to clarify - there are different ways to count the quantum fields, just as there are different ways to count particles, as the article points out. You really need to specify the premises you're using to count them. But either 17 or 37 are natural counts. 17 is a somewhat simplified version, which ignores quark color charges and groups the W and Z bosons together.

Here's how the list of 37 typically breaks down:

18 quark fields: 6 flavors x 3 colors

3 charged leptons: electron, muon, tau

3 neutral leptons: neutrinos corresponding to the charged leptons

12 gauge bosons: 1 photon, 3 electroweak bosons (Z, W+, W-), 8 gluons

1 Higgs boson

(Note: this refers to fields as we observe them today, essentially counting what are known as Dirac fields. These are not the more fundamental fields that were present before the electromagnetic force separated from the weak nuclear force in the early universe, a process known as electroweak symmetry breaking. More on this below.)

In writing that list out, I realized that it skips one of the properties the article mentioned: chirality. If we take that into account, the number of charged lepton fields doubles to 6, and we have 40 fundamental quantum fields.

The reason that distinction is often ignored is that at everyday energies, the left- and right-handed components of particles are essentially blended together, so experiments don’t see them as separate particle types. Treating left- and right-handed chirality as a single field is a simplification of the underlying electroweak theory. Treating them as distinct particles, as the article does, is actually a bit dubious.

Re electroweak symmetry breaking, if we're really looking for "fundamental", then it makes sense to look at the fields before symmetry breaking. In a very real sense, these are more fundamental, because they give rise to the fields we observe.

But, that gets into fields that most non-physicists won't recognize, and that don't even have good names: the weak isospin gauge fields W^1_\mu,\; W^2_\mu,\; W^3_\mu,\; and the hypercharge field B_\mu.

In that scenario, there are 4 Higgs fields, which brings the total field count to 43. After symmetry breaking, those extra 3 Higgs fields became longitudinal polarization modes of the electroweak bosons, which are not counted as extra fields. The article mentions this, "the W+, W−, and Z bosons have a third, “longitudinal” polarization state as well," and adds them to its particle count.

We can relate this all back to the article as follows:

1. To count antiparticles, group the quarks and leptons into fermions - 18 + 3 + 3 = 24, and double that to count antiparticles, giving 48. Bosons are their own antiparticles, so their count doesn't change. The total particle count is now 48 fermions + 12 gauge bosons + 1 Higgs = 61.

2. For spin/polarization, double the number of fermions again to 96, double the number of gluons from to 16, multiply photons by 2, multiply the 3 electroweak bosons by 3 giving 9. This gives 96 fermions + 2 photons + 16 gluons + 9 electroweak bosons + 1 Higgs boson = 124 particles.

That 124 is 6 more than the 118 mentioned in the article, but again it depends on exactly what you're counting. Chirality in particular complicates things, because of the blending issue I mentioned earlier.

Re: How Many Elementary Particles Are There, Really?

#75
post #62

Physicist here. I don’t buy some of these distinctions, like the chirality. Chirality is an observable, it’s like saying there are two photons because they can come in two polarizations, but polarization is not an inherent property: it depends on how we measure it. So I could describe any photon in the left/right chiral basis just as well as in the vertical/horizontal basis or any two antipodal points in the Poincaré…

chirality is how particles get mass - the Higgs field gives fermions mass by coupling their left and right-chiral parts, causing chirality mixing

Re: How Many Elementary Particles Are There, Really?

#76
post #57

I'm not a physicist (so take this with a grain of salt) but I have spent a lot of time trying to find an answer to this question. If you interpret the physics before Spontaneous Symmetry Breaking as more fundamental, and you treat the antimatter fields as distinct, then I think you can reasonably claim that there are 30 fundamental fermion fields. Specifically, in each of the 3 generations, you have: 1. The left-hand…

that's pretty impressive for a non-physicist (assuming no LLM)

Re: How Many Elementary Particles Are There, Really?

#77
post #61
post #25

Earlier quoted context omitted.

Yes, the field is the substrate. "I insist upon the view that 'all is waves'." Letter to John Lighton Synge (9 November 1959), as quoted by Walter Moore in Schrödinger: Life and Thought (1989) ISBN 0521437679 It is not a breakthrough, it is just something we refuse to see, something that was known for a century. "All is a wave" is the unifying principle. I am no mathematician, but the math needs to start with that fu…

> I am no mathematician, but the math needs to start with that fundamental principle. This is a weird sort of hubris. “I’m not qualified to do this job but I can certainly tell you how it needs to be done.” > And if everything is a wave there are no discrete quantities beyond our definition of what constitutes the end, or borders, of the wave. This is not true in multiple ways. First, it’s known that these particles…

> This is a weird sort of hubris. “I’m not qualified to do this job but I can certainly tell you how it needs to be done.”

A quantum state is a mathematical entity that represents a physical system. Since waves are not physical can you see where I can assume that the math needs to start from a different place? If it is even useful at all?

> it’s known that these particles exhibit quantum behavior. Many measures are in fact quantized.

To measure is to quantize, so this is circular reasoning. If particles are always waves we would still see the quantum behavior.

> Second, existing as a wave does not mean no discrete quantities.

Where is the precise point a standing wave ends and begins? The best we can do is guess with calculus and differential equations. Again, yoiu are quantifying things that in and of themselves are not quantized outside of our conception.

Re: How Many Elementary Particles Are There, Really?

#78
post #22
post #8

Earlier quoted context omitted.

> They're manifestations of fields. Or wave. Everything is a quantum wave. https://www.vlatkovedral.com/everything-in-the-universe-is-a...

A wave is a phenomenon that propagates through a field - i.e. the field is what allows the wave to exist. (The philosophy of that admittedly gets messy, though, e.g. "are fields real objects?")

Yes, very messy and ultimately unknowable.

Re: How Many Elementary Particles Are There, Really?

#79
post #30

There are also 17 wallpaper groups. That always seemed like a funny number. I know it's a long shot, but is there a relation?

As the article explains, counting is very hard.

IMHO, I like to count the x3 colors of quarks and the x2 chirality of bosons. So I get 16*3 fermions and 1+8?+3?+1 bosons, in total 61 but the number of bosons is not a hill I will do die on.

On the other extreme, there are some proposal to reduce the number of particles, in particular it makes a lot of sense to consider the electron and neutrino as a single class of particle, and the up and down quark as a single class of particle, so I guess the number goes down to 6 fermions + 4 bosons = 10? in total (I'd keep chirality, so perhaps 12+4=16?).

And there are even more extreme proposals to consider quarks and leptons in a single bag of mud. In particular this was popular like twenty years ago, but the experiments disagree (IIRC by a small amount, IIRC it's not a very bad approximation) https://en.wikipedia.org/wiki/Georgi%E2%80%93Glashow_model I tried to count the particles there and I gave up, let's say a lot.

And you still have to add gravitons (and their weird cousin particles) and perhaps more than one Higgs bosons. So the number should increase in the future.

And there are still ideas to add a global x2, because it would be nice if every bososn has an undiscovered fermion companion and vice versa. IIRC it's falling out of fashion because the simple versions don't agree with the experiments https://en.wikipedia.org/wiki/Supersymmetry but it sounds interesting :(

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In conclusion: Don't get too attached to the number 17.

Re: How Many Elementary Particles Are There, Really?

#80
post #43
post #32

D

Hmm if a particle is a quantized packet of a field, then if multiple quantizations are possible in a field, then it's possible for more particles than fields?

it's called quantum occupation number - literally how many particles (packets) are at a particular point in space-time. only for boson fields.

think like the intensity of a RGB pixel - R can be 1, or maybe 10 for a particular pixel, thus you have 10 red "packets"

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