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How Many Elementary Particles Are There, Really?

quantamagazine.org

111–120 of 160 posts

Re: How Many Elementary Particles Are There, Really?

#111
post #104
post #73

Earlier quoted context omitted.

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…

I'm a bit surprised that the weightier generations of fermions are categorized as fundamentally different fields. Is this a crutch/temporary classification that we expect to be resolved with further research, or are there real indications that the apparent similarities between e.g. up/charm/top are fully independent manifestations?

I can speak definitively on behalf of the Standard Model here:

"No idea, bro!"

It's one of the biggest open questions about the Standard Model, and it's considered an indication that the model is probably incomplete.

Btw you mentioned "weightier generations", but mass is a consequence of the difference between the generations, not the fundamental difference. Before electroweak symmetry breaking, those particles had no mass, but they already existed as three distinct generations, with different Yukawa couplings. When the Higgs field acquired a vacuum expectation value, those different couplings became different masses.

The Standard Model treats the number of generations and the Yukawa couplings as fundamental inputs to the theory. There's a Nobel Prize waiting for whoever figures out whatever might be behind this.

Even string theory doesn't solve this. Calabi-Yau manifolds provide a model which could explain it in theory, but no actual, concrete solution has been found.

Re: How Many Elementary Particles Are There, Really?

#112
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…

> it’s like saying there are two photons because they can come in two polarizations

The article claimed exactly that! It said, "Not everyone counts these different chiral and polarization states as distinct particle types. Yet it’s logical to do so, because they affect how particles behave and interact."

At one point the author reaches a particle count of 118. This corresponds to the degrees of freedom of the on-shell physical states (polarizations, spin orientations, colors, and antimatter) of all particles in the Standard Model. As you say, it's misleading to call this a count of different particles.

Re: How Many Elementary Particles Are There, Really?

#113
post #77
post #61

Earlier quoted context omitted.

> 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 i…

Either you understand this stuff at a level so much deeper than me that I can’t comprehend what you’re getting at or you are way out of your depth because none of this makes any sense to me.

Waves aren’t physical but everything is waves? We can’t measure standing waves but have to “guess” with calculus and differential equations?

Re: How Many Elementary Particles Are There, Really?

#115
post #87
post #9

Earlier quoted context omitted.

How long can you break something apart until you cannot any longer? The things we are breaking apart are illusions in a sense. There will always be a smaller particle because that is what we are looking for. When we understand that everything that we see is a manifestation of a probability wave, then we will understand everything is a wave and end these foolish experiments.

planck scale is the theoretical limit to disassembly.

its only the limit we can probe things. just because we can’t measure something doesnt mean nature cant operate at that scale

Re: How Many Elementary Particles Are There, Really?

#116
post #35

Earlier quoted context omitted.

...and a field is just a value that behaves in a particular way. An example outside QFT: phonons [1] behave like particles, but there is no "palpable" sound field, there's only local distribution of implulses of the molecules of air (or whatever medium) where the sound propagates. Other fields can be seen as attributes of the space itself , and "elementary particles" as wrinkles on it. Gravity is special because it b…

> Gravity is special because it bends the very geometry of space. It's important to remember that this is not true in QFT, and QFT is not true in GR. That is, the math of QFT does not work if spacetime can become curved (at least, if it can become significantly curved).

Maybe you want to leaf through a copy of Birrell & Davies or Parker & Toms again. QFTCS is good in strong gravity, and is as good as anything else at transplanckian scale (which is to say there's presently no way of knowing when around there QFTCS becomes a bad approximation to an unknown quantum gravity).

We should also remember the enormous cosmological curvature in which testable quantum systems exist; it's not just about compact objects. Significant? There's observed H-sources above z ~ 15, and of course the CMB photons at z ~ 1100. Indeed, B&D deals with Robertson-Walker spacetimes over several chapters before they get to black holes.

Also at the weak but measurable curvature regime there's e.g. Pound-Rebka, time metrology[1], and so forth, and lots of spacecraft confirming the strong equivalence principle (e.g. MESSENGER, LAGEOS) and thus supporting the LLI one expects to find in relativistic QFTs of the sort one would use to describe the behaviour of laser altimeters, distant astrophysical masers (and the Lyman-alpha forest), the spectral lines in stellar atmospheres and so on.

[1] just because it's neat and directly relevant to your comment: https://journals.aps.org/prxquantum/abstract/10.1103/q188-b1... [2025]

Re: How Many Elementary Particles Are There, Really?

#117
post #87

Earlier quoted context omitted.

planck scale is the theoretical limit to disassembly.

its only the limit we can probe things. just because we can’t measure something doesnt mean nature cant operate at that scale

actually the idea is that nature cant operate at that scale.

the thing about planck units is they are extrapolations that end at single planck length that has some problems just with basic geometry, as well as a supposed instability of a planck space spontaneously collapsing.

a planck unit volume must take a form that has dimensions of single planck units and pack together so that no smaller spacings are created. it cant be a sphere, at best it can be some sort of riemannian tetrahedron or triangle.

it would be conveinient if that level was a 2D plane, but it still has issues.

Re: How Many Elementary Particles Are There, Really?

#118
This and not being able to divide by 0 in math always drove me up the wall in school. Encountering a god level difficulty unsolved problem in the first 5 minutes of discussion around the basics of the field and then shrugging and continuing to build castles of complexity atop the seemingly rickety foundation irrationally irked me.

Feels good to get that off my Chest. I’ve been holding it in for ~20 years

Re: How Many Elementary Particles Are There, Really?

#119
post #25

Earlier quoted context omitted.

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.

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…

> It is not a breakthrough, it is just something we refuse to see, something that was known for a century.

This sounds like you're about to try selling me a crystal and a magic ritual. The wording here is far too grandiose, and I assure you physicists are not "refusing to see" that "everything is a wave". Whatever you imagine that might mean.

> The very notion of calling it "qunatum" physics is probably wrong since quantum is "a discrete quantity of energy proportional in magnitude to the frequency of the radiation it represents."

> And if everything is a wave there are no discrete quantities beyond our definition of what constitutes the end, or borders, of the wave.

Mumbo-jumbo.

It's called "quantum" physics because of the discovery that many parts of nature do indeed exist in discrete steps. Yes, electron orbitals are described with wave functions - that is, the electron exists as a probability cloud, but the functions themselves are still discrete! When an electron gains energy, it jumps from one orbital to another without passing through a continuous state in the middle. That is the fundamental insight of Quantum Mechanics - energy, momentum, etc are all quantized and not actually continuous.

The wikipedia article on quantum mechanics literally covers this in the intro - https://en.wikipedia.org/wiki/Quantum_mechanics

Re: How Many Elementary Particles Are There, Really?

#120
At least for the fermions the answer is a nice power of two for each generation. There is the electron, the neutrino, the red, green and blue up quark and the red, green and blue down quark, giving 8 fermions per generation. Since one can distinguish between particles and antiparticles, one could also argue for 16 fermions per generation. Also one can distinguish between left and right handed particles, giving a total of 32 fermions per generation.
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