Question about protons

A couple of weeks ago, the science section of the NYTimes had an article about protons. The article said that scientists now believe that protons aren’t sphere shaped, but can also be shaped like a doughnut, etc. And that the protons shape can change.

I can understand that and I don’t have a big problem with it.

But then the article started talking about the particles that make up protons ie; quarks and gluons. According to the article the theory is that there are "theoretical pgliuns and anti-gluons which wink in and out of existence."

Huh??? How is this possible?

Also, the article mentioned how these gluons theoretically would give off energy comparable to a black hole.

If that’s true, (and if it is, would someone please explain how) I would think that our bodies would catch fire due to the tremendous amount of energy.

It may be related to vacuum energy AKA quantum fluctuations, particles spawning in and out of existence out of nowhere…
Theorically the whole universe sprang into existence on one of those vacuum fluctuations, so a virtual particle with the same theorical energy as a black hole wouldn´t be a problem.
Perhaps someone with a better grasp of quantum mechanics would give a better answer. :wink:

Gluons winking in and out of existence isn’t all that exotic; the same thing happens with photons. The electro-magnetic force is carried by photons which travel from one charged object to another.

I don’t know what they mean by the energy of a black hole, but black holes of different sizes give off different amounts of energy. Bigger black holes give off less. Black holes as big as the ones you find in nature give off very very very little amounts of energy, like 10[sup]-30[/sup] Watts.

I thought a proton was shaped like a triangle…its made up of three quarks, isn’t it?

Well, yes, it’s made of three quarks (plus a whole bunch of gluons and quark-antiquark pairs); you can actually see that (or really, infer that) by certain experiments which essentially shoot things at protons and see what happens when they bounce off. Nonetheless, the quarks are rattling around in the proton in a way which is pretty much spherically symmetric, making the proton appear to be rather like a sphere.

Does it really make sense to talk about the shape of protons? Or is this just our attempt at fitting something into our view that’s completely unlike anything we know?

Honestly? No, it really doesn’t make a lot of sense, IMO, but it’s one of those things that sounds good.

That’s kinda what I thought.

If the quarks are hoping around then the shape of a proton would be a cloud of probabilities; you know the old uncertainty principle.

It may not be exactly what we think of when we say “shape”, but I think it’s reasonable to talk about proton’s shape. An object with a spherically symmetric wave function, like an s electron orbital, can reasonably be said to be spherical.

I agree. It sounds like the Times article was referencing spherical harmonics. I know very little about particle physics, but it seems reasonable that the quarks and whatnot could be described by a spherically symmetrical wave equation that allows non-symmetrical solutions.

Either this or they were bringing in some string theory (which I know almost nothing about).

Wait…so protons (and others) are no longer considered point particles? Is this because of string theory (whereby the smallest unit of matter is an n-dimensional loop of string)? Also, due to the Uncertainty Principle, since the location of the quarks within a proton is very well nailed down (i.e., within the “volume” of the proton), does that mean that the uncertainty in the velocity is hugely uncertain? i.e. individual quarks have a velocity between (0 + epsilon) and c ?

A little off topic but why then don’t we see photons travelling between magnets?

rather than talking about the shape of the proton it is probably proper to talk about the shape of it’s probabilty distribution which appears to be spherical (NY Times article notwithstanding).

mooka, you get photons wherever there is an electric current, so for eample if an electric current is induced by a magnet, you do get photons. These phons though have very, very low frequencies and exhibit a very wave like nature (as opposed to particle-like nature) and manifest themselves in the form of electrical interference.

Actually, there are two reasons we don’t consider protons point particles. First and far more importantly, we find by observation that they aren’t. Secondary in importance is that in the Standard Model, which we rather like, protons are made up of three quarks, plus a boatload of virtual particles hopping around.

Ignoring string theory at the moment, the list of particles we believe to be points goes something like:
[li]leptons (electron, muon, tau, neutrinos, associated anti-particles)[/li][li]quarks (and anti-quarks, of course)[/li][li]photons, gluons, and the force carriers for the weak force (the W[sup]+[/sup], W[sup]-[/sup], and Z)[/li][li]gravitons (I presume they exist)[/li][li]Higgs (likewise)[/li][/ul]

Yeah, the momentum of the quarks is rather broadly uncertain.

The main problem is the use of the word “particle.” Particles, as field theorists use the term, are not like little ball bearings, although they are the closest thing to in the quantum realm.

The fundamental entities in quantum theory are fields. A field is something has a “value” at every point in a region of space. For instance, you can talk about temperature field (scalar), the value of the temperature at various points. Fields can also be vector (Newtonian gravity, flow in a liquid), tensor (gravity, stress in a solid).

“Particles” are theorists shorthand for various modes of excitation of field – kind of like a standing wave on a string. And like a wave on a string, a particle need not be localized in space. Also just like two waves can cancel each other, two particles can cancel each other out (if one is the anti-particle of the other).

First piece of advice: Completely ignore any scientific article you read in the New York Times or similar publications. When scientific stories make it into popular (i.e., non-scientific) publications like the Times, they’re generally either so oversimplified as to be nearly meaningless, or on a “new” discovery which has been known for decades, or some combination of the two. At best, they can provide some good search terms for more information.

But as for point particles: Protons are definitely made of quarks (well, as definite as anything can be in particle physics), so they’re not points. The leptons, quarks, weakons, and (I think) Higgs are currently believed to be point particles: In the case of the charged leptons, this is from experiment (if they have any non-point structure, it’s really really small), but for the others, I suspect it’s mostly just a matter of simplicity of the model: It’s really hard to measure most elementary particles, so lacking any evidence to the contrary, Occam tells us to consider them points. For the massless particles (photons, gluons, and the hypothetical gravitons), I’m not sure if it’s possible to meaningfully say that they’re point particles.

I suppose my contention is that essentially, a fundamental particle oughtn’t have any internal structure, in that if it did, we’d probably wind up explaining said internal structure in terms of yet another set of particles. I’ve been somewhat cavalierly using “point particle” and “particle which has no internal struture” interchangeably.

You’re quite possibly right to suggest that it’s not particularly meaningful to say that a massless particle is a point, but of course it’s certainly meaningful to say that a massless particle isn’t a bound state of yet other particles.

A bit of a hijack… but this question has been bothering me for some time: what keep the protons in an atomic nucleus from repelling each other out of it?

That’s what the strong force does, basically. It binds quarks together to make protons, and it binds quarks in different protons and neutrons together to make nuclei.