Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

How Many Elementary Particles Are There, Really?

quantamagazine.org

Post reply on HN
Print view View original

31–40 of 160 posts

Re: How Many Elementary Particles Are There, Really?

#31

Post by tsimionescu »

HarHarVeryFunny wrote: post #26
jerf wrote: post #6

Earlier quoted context omitted.

You don't have to wonder, because they are. They're manifestations of fields. I think it is a reasonable answer to tell people "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". That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecif…

But of course one can then question why are there exactly N different types of fields, with their specific types of interaction (at least in our universe)? Why should we suppose that this is the most fundamental description of reality, rather than being emergent from something else?

Well, why would there be fewer than N? There is no general principle that we can impose on the world, it just is, we can only discover what the laws and components of the world are (hopefully). I'm not claiming it's impossible for there to be fewer fields than we think right now. But there is no reason to believe there should be.

Re: How Many Elementary Particles Are There, Really?

#33

Post by unholiness »

Stopped reading after "Yet in the mathematical equations that define the Standard Model, the eight gluons are distinct from one another in the same way that the W and Z bosons differ."

W and Z bosons, photons, etc have fixed masses, charges, interaction strengths with other particles. These properties can exactly be listed and looked up in a table of elementary particles with discrete rows.

Gluon color is continuous property in a vector space. Gluons can have any color in that space, with any combination of the 8 basis vectors (and that choice of basis is also completely arbitrary). The color |g1> is no more valid than the color (|g1> + |g2> + |g8> / √3) or any other of infinite combinations.

Calling this "8 gluons" is like saying there's "3 photons" because they can have momentum in 3 dimensions. If you want to argue there's infinite kinds of gluons, go ahead, but there aren't 8.

Re: How Many Elementary Particles Are There, Really?

#34

Post by AnimalMuppet »

antonvs wrote: post #20
jerf wrote: post #6

Earlier quoted context omitted.

You don't have to wonder, because they are. They're manifestations of fields. I think it is a reasonable answer to tell people "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". That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecif…

> 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?

Re: How Many Elementary Particles Are There, Really?

#35

Post by nine_k »

TheOtherHobbes wrote: post #18
jerf wrote: post #6

Earlier quoted context omitted.

You don't have to wonder, because they are. They're manifestations of fields. I think it is a reasonable answer to tell people "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". That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecif…

In QFT every particle type has its own field.

...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 bends the very geometry of space.

[1]: https://en.wikipedia.org/wiki/Phonon

Re: How Many Elementary Particles Are There, Really?

#36

Post by jerf »

HarHarVeryFunny wrote: post #26
jerf wrote: post #6

Earlier quoted context omitted.

You don't have to wonder, because they are. They're manifestations of fields. I think it is a reasonable answer to tell people "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". That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecif…

But of course one can then question why are there exactly N different types of fields, with their specific types of interaction (at least in our universe)? Why should we suppose that this is the most fundamental description of reality, rather than being emergent from something else?

I completely agree that's a reasonable question.

I'd also observe that between dark matter and dark energy, there's good reason to believe that we may not have a full accounting of all fields.

I am just observing that if you have a non-scientist asking the question "how many fundamental particles are there", with the expectation that "995.5" is not really the right answer, "the number of fields" is a reasonable response that probably gets closer to what they are looking for. Even if someday someone does get them to all be some manifestations of a single field it would arguably still be the case that people are more interested in the answer of the current number of fields then being told "1", because "1" is in many ways not a helpful answer to "how many types of things are there". Even if there is a profound sense in which it was true, there would still be a profound sense in which it was false, too.

Re: How Many Elementary Particles Are There, Really?

#37

Post by HarHarVeryFunny »

tsimionescu wrote: post #31
HarHarVeryFunny wrote: post #26

Earlier quoted context omitted.

But of course one can then question why are there exactly N different types of fields, with their specific types of interaction (at least in our universe)? Why should we suppose that this is the most fundamental description of reality, rather than being emergent from something else?

Well, why would there be fewer than N? There is no general principle that we can impose on the world, it just is, we can only discover what the laws and components of the world are (hopefully). I'm not claiming it's impossible for there to be fewer fields than we think right now. But there is no reason to believe there should be.

I'm not saying fewer fields, but perhaps a more fundamental substrate to reality than fields that fields emerge from. Maybe the N fields are just vibrational modes or attractor dynamics of something simpler.

It seems there has to be a reason WHY there are exactly N fields, and WHY they interact in the ways they do.

Edit: As I noted in another comment, the best explanation may come down to "there are only 100 viable types of universe, and ours is type 42". I'd be happy with that.

Re: How Many Elementary Particles Are There, Really?

#38

Post by [deleted] »

HarHarVeryFunny wrote: post #26
jerf wrote: post #6

Earlier quoted context omitted.

You don't have to wonder, because they are. They're manifestations of fields. I think it is a reasonable answer to tell people "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". That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecif…

But of course one can then question why are there exactly N different types of fields, with their specific types of interaction (at least in our universe)? Why should we suppose that this is the most fundamental description of reality, rather than being emergent from something else?

[deleted]

Re: How Many Elementary Particles Are There, Really?

#39

Post by frutiger »

HarHarVeryFunny wrote: post #26
jerf wrote: post #6

Earlier quoted context omitted.

You don't have to wonder, because they are. They're manifestations of fields. I think it is a reasonable answer to tell people "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". That doesn't invalidate this question in general, though the number of different answers from people looking at the same thing suggests it may be underspecif…

But of course one can then question why are there exactly N different types of fields, with their specific types of interaction (at least in our universe)? Why should we suppose that this is the most fundamental description of reality, rather than being emergent from something else?

> But of course one can then question why are there exactly N different types of fields, with their specific types of interaction (at least in our universe)?

Even that has a (still unsatisfactory) answer.

Poincaré symmetry imposes constraints on the kinds of fields we can have. Gauge symmetry shows us how they may couple.

There are still some arbitrary selections of the possible permutations that nature has “picked”.

Re: How Many Elementary Particles Are There, Really?

#40

Post by pdonis »

unholiness wrote: post #33

Stopped reading after "Yet in the mathematical equations that define the Standard Model, the eight gluons are distinct from one another in the same way that the W and Z bosons differ." W and Z bosons, photons, etc have fixed masses, charges, interaction strengths with other particles. These properties can exactly be listed and looked up in a table of elementary particles with discrete rows. Gluon color is continuous…

> W and Z bosons, photons, etc have fixed masses, charges, interaction strengths with other particles.

But you can form a continuous set of linear combinations of these things, just as you can with gluons. Indeed, what the article calls W and Z bosons (and photons) are just such linear combinations--the ones that appear in the low energy limit after the electroweak phase transition occurs. Before that phase transition, different linear combinations (i.e., a different basis of the electroweak vector space) are the ones that naturally appear. So saying that there are two W, one Z, and one photon is really counting basis vectors in the electroweak vector space, just as saying there are 8 gluons is really counting basis vectors in the gluon sector of the strong interaction vector space.

Post reply on HN