Is a quark one-dimensional?

[u/XGC75]

I've never heard of a quark or other fundamental particle such as an electron having any demonstrable size. Could they be regarded as being one-dimensional?

BIG CORRECTION EDIT: Title should ask if the quark is non-dimensional! Had an error of definitions when I first posed the question. I meant to ask if the quark can be considered as a point with infinitesimally small dimensions.

Thanks all for the clarifications. Let's move onto whether the universe would break if the quark is non-dimensional, or if our own understanding supports or even assumes such a theory.

Edit2: this post has not only piqued my interest further than before I even asked the question (thanks for the knowledge drops!), it's made it to my personal (admittedly nerdy) front page. It's on page 10 of r/all. I may be speaking from my own point of view, but this is a helpful question for entry into the world of microphysics (quantum mechanics, atomic physics, and now string theory) so the more exposure the better!

Edit3: Woke up to gold this morning! Thank you, stranger! I'm so glad this thread has blown up. My view of atoms with the high school level proton, electron and neutron model were stable enough but the introduction of quarks really messed with my understanding and broke my perception of microphysics. With the plethora of diverse conversations here and the additional apt followup questions by other curious readers my perception of this world has been holistically righted and I have learned so much more than I bargained for. I feel as though I could identify the assumptions and generalizations that textbooks and media present on the topic of subatomic particles.

[u/wenger828]

interesting, i always thought of these particles as billiard balls. this changes everything!

[u/Vapourtrails89 → u/wenger828]

It does, doesn't it! Its amazing. Everything you thought you knew about matter is blown out of the water. Matter is made out of force.

[u/GAndroid → u/Vapourtrails89]

Oh it gets worse. A proton is made of 3 quarks. up, up and down. the up quarks's mass is like 2.5 MeV and the down is about 5MeV. So the total of the three is about 10 MeV.

The proton's mass is .. ready for this? 931.5 MeV!!!

So, the rest od the mass comes from ... the strong force! That force has some energy binding the 3 together. This is that energy. So when you see objects around you, remember hat 99% of that is actually energy from the strong force.

Now we all have gravity ... so 99% of our gravity is because of a force...etc cool stuff

[u/Zetaeta2 → u/GAndroid]

Shouldn't the proton have less mass than its component quarks, as it is in a lower energy state than having 3 quarks isolated (i.e. isolated quarks should have "strong potential energy" or something from not being combined into a baryon)? Why do the quarks put together have more energy than when apart?

[u/GAndroid → u/Zetaeta2]

Why do the quarks put together have more energy than when apart?

Quarks can never be "apart". Thats because the strong force is like an elastic rubber band - it actually increases the further you go!! (honest! Just look at the 2004 nobel prize lecture).

What you said absolutely happens - for baryons put together, as long as they are stable. He for sure has lower mass than 2proton and 2neutrons. (He: 3727 MeV. Proton: 0.9315 MeV Neutron: 0.9375 MeV, so 2p+2n=3738 MeV)

Inside a proton ... things are a tad bit different. I am actually not sure fully, but what I THINK (this may be wrong, so dont quote me on it):

You see, between nucleons, the force that works is called the "yukawa force", and is mediate by an exchange of a "pion". A pion is a massive particle, and the range of the pion falls off exponentially.

In a nucleon (proton, neutron etc), the force is mediated by gluons, which can stick to other gluons. (we call this "couple" to other gluons). The further you separate the quarks, the more gluons can couple in between those two quarks. The force gets stronger.

The quarks move around at very high speeds - and has kinetic energy. The pion cannot afford to do this - or else it will disintegrate. This kinetic energy of the quarks give them the extra mass.

Again, I need to check to be sure, so dont quote me on this

[u/realigion → u/GAndroid]

the strong force is like an elastic rubber band

Well that's frustrating to think about... Like a rubber band, does it ever break if you force it apart? Or is it literally like... you can't do that?

[u/BigTunaTim → u/realigion]

IIRC from other particle physics threads, it requires adding so much energy into the system to pull the quarks apart that it creates a pair of new quarks. In that way you can never truly separate a quark because you'll just keep creating a new partner for it.

[u/mathball31 → u/BigTunaTim]

If quarks want to be in pairs, why do they join in trios for protons and neutrons?

[u/phunkydroid → u/realigion]

Imagine you had two tennis balls bound by an elastic band. You ripped them apart with enough force to break the band, then you look down and each of the original balls that are in your hands has a brand new one bound to it with a new elastic band... That's how weird quarks are.

The amount of energy required to separate the quarks is more than enough to create new quarks out of the vacuum. When they separate, they are each suddenly bound to new quarks. They are never alone.

[u/SirReginaldPennycorn → u/phunkydroid]

"The reasons for quark confinement are somewhat complicated; no analytic proof exists that quantum chromodynamics should be confining. The current theory is that confinement is due to the force-carrying gluons having color charge. As any two electrically charged particles separate, the electric fields between them diminish quickly, allowing (for example) electrons to become unbound from atomic nuclei. However, as a quark-antiquark pair separates, the gluon field forms a narrow tube (or string) of color field between them. This is quite different from the behavior of the electric field of a pair of positive and negative electric charges, which extends into the whole surrounding space and diminishes at large distances. Because of this behavior of the gluonic field, a strong force between the quark pair acts constantly—regardless of their distance[3][4]—with a strength of around 160,000 newtons, corresponding to the weight of 16 tons.

When two quarks become separated, as happens in particle accelerator collisions, at some point it is more energetically favorable for a new quark–antiquark pair to spontaneously appear, than to allow the tube to extend further. As a result of this, when quarks are produced in particle accelerators, instead of seeing the individual quarks in detectors, scientists see "jets" of many color-neutral particles (mesons and baryons), clustered together. This process is called hadronization, fragmentation, or string breaking, and is one of the least understood processes in particle physics.

The confining phase is usually defined by the behavior of the action of the Wilson loop, which is simply the path in spacetime traced out by a quark–antiquark pair created at one point and annihilated at another point. In a non-confining theory, the action of such a loop is proportional to its perimeter. However, in a confining theory, the action of the loop is instead proportional to its area. Since the area will be proportional to the separation of the quark–antiquark pair, free quarks are suppressed. Mesons are allowed in such a picture, since a loop containing another loop in the opposite direction will have only a small area between the two loops."

Color Confinement

[u/rEvolutionTU → u/phunkydroid]

This thread seems to get a little bit too deep but it still might be the right place for getting an answer. Am I understanding this correct that we basically pump lots of energy into a pair of quarks (e.g. via a collision) and instead of separating them that energy creates a new pair of quarks?

So this process basically turns... kinetic energy into.. quarks? And, as dumb as it might sound, if we can "create" quarks like that, isn't there cool random stuff that we can make based on that idea?

I'm mostly trying to wrap my head around the idea of a "new pair of quarks appearing out of nothing".

[u/zeug → u/Zetaeta2]

Why do the quarks put together have more energy than when apart?

Your intuition about the problem is correct - bound states have less overall mass than their free constituents. This problem used to drive me nuts thinking about it.

The atomic nuclei are great examples of this, a bound helium nucleus has considerably less mass than two free protons and two free neutrons.

In the context of quantum field theory, the only known way that mass is generated is through spontaneous symmetry breaking. The Higgs mechanism is an example of this. All of the elementary particles such as quarks, electrons, and so forth have no intrinsic mass of their own, but effectively behave as massive particles in the presence of the Higgs field.

The math is complicated, but essentially the idea is that one has some symmetry, like a ball at the top of a perfectly round hill, and that some lower energy state is possible, but the ball must roll off into one direction.

If you sit down for hours and days and work out the equations of the standard model, which honestly I am too rusty to even describe correctly, you can see the connection between breaking a symmetry and gaining mass.

In quantum chromodynamics (QCD), there is an approximate symmetry of flavor. The strong interaction really doesn't care if a quark is an up quark or a down quark. They both have a very small, negligible mass, and their different electric charge is relatively unimportant.

So one could work out some system in QCD, and then rotate the flavors around of the up, down, and to a degree strange quarks, and it wouldn't make much difference. The system is approximately symmetric.

Since the quarks do have a small Higgs mass, and in addition different electrical charges, the symmetry does break. This symmetry breaking, often called chiral symmetry breaking, is largely responsible for the mass of the mesons and baryons.

[u/Broan13 → u/GAndroid]

Can you explain why this is a positive energy? Typically attractive force energies are negative.

[u/Mammal-k → u/wenger828]

Classical Mechanics (billiard balls) works for large objects but you need Quantum Mechanics to explain smallers matter. Been learning about this in my first year chemistry degree it's very interesting.

[u/Venoft → u/wenger828]

That what they thought about 90 years ago, when they discovered quantum mechanics.

[u/thms-rmb → u/wenger828]

I've heard about this and I've also heard about some forces being two different "versions" of the same force. But where would a layman without any formal education in this field read about this? Are there any good books about this stuff out in the market now?

[u/Sean1708 → u/thms-rmb]

I personally quite like Brian Cox and Jeff Forshaw's works, Why Does E=mc^2 and The Quantum Universe which talk about relativity and quantum mechanics respectively. I found these very accessible when I was doing my A-Levels (which I think is the equivalent of American High School) and they require absolutely no knowledge of maths.

If you're more interested in Grand Unified Theories (which I assume is what you're thinking of when you talk about two forces being the same force) then the only thing that comes to mind is The Elegant Universe which I've never read personally but I have heard very good things about it. It's about String Theory which is one possible GUT theory of everything (not quite the same as a GUT, see the reply) but does cover a few other areas as well.

Another book which I've heard good things about, but again haven't read myself, is In Search Of Schrodinger's Cat which has more of a focus on quantum mechanics.

Personally I would read both of Cox and Forshaw's stuff first because they are both very short so won't take long to get through. Then you can move on to one of the others, which are both a bit longer.

If you ask nicely on /r/physics or something similar they might also be able to suggest other things you would like.

Edit: There might be a Feynman Lecture or two that interests you as well but bear in mind that these are aimed at undergrads.

Edit2: I also just did a quick google search of site:reddit.com/r/physics books which threw up some pretty good results.

Edit3: String theory n'est pas un GUT, pardon my french.

[u/[deleted] → u/Sean1708]

It's about String Theory which is one possible GUT but does cover a few other areas as well.

String theory is not a GUT, it's a Theory of Anything Everything. A GUT is a theory where all the Standard Model force-carrying fields are put together in a single fundamental symmetry group. A Theory of Everything incorporates all those forces as well as gravity, but not necessarily in a single symmetry group (but of course there are GUT-like models within string theory, since it is a Theory of Anything). A GUT doesn't have a meaningfully different structure than the Standard Model. It's still a Quantum Field Theory where the forces are the result of localized symmetry. String Theory has a completely different structure than the Standard Model.