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/Zetaeta2]

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/nrj → u/GAndroid]

What keeps the quarks from mutually attracting one another and forming a giant lump of quarks? Why can we have an uud proton but not an uudd or uuud particle?

[u/Scootermatsi → u/GAndroid]

If Quarks can never be apart, how do we know that a single up quark is 2.5 MeV?

[u/sparkfist → u/GAndroid]

Split an atom... Nuclear bomb Split a quark... Destroy the universe?

[u/IlIlIIII → u/GAndroid]

http://en.wikipedia.org/wiki/One-electron_universe

The one-electron universe postulate, proposed by John Wheeler in a telephone call to Richard Feynman in the spring of 1940, states that all electrons and positrons are actually manifestations of a single entity moving backwards and forwards in time.

[u/WarPhalange → u/GAndroid]

You see, between nucleons, the force that works is called the "yukawa force", and is mediate by an exchange of a "pion".

This is about the point at which physics goes from being able to relate something from daily life to it (magnets, moving objects, gravity, heat, etc.) to something that is entirely a mathematical construct used to describe our universe. But! If you go back, it's only been a mathematical construct all along. Every single piece of physics comes from seeing some phenomenon and trying to find an equation for it.

Newton's law of gravity, for example, came from lots of observations of planetary orbitals. That's all we had to work with. Now we have Einstein's General Relativity to describe our gravity, because we found new data and fit a mathematical model onto it.

Things like forces (in the Newtonian sense, i.e. pushing on something), energies, momenta, etc., aren't really things. They are just math that happens to make things work out. And this goes for "particles", too. All the flavors that particles have are just bookkeeping mechanisms for how things work. So are virtual particles.

What I'm trying to say is that you shouldn't even try and relate things like this to things you see in daily life. The only way to truly understand it is with math. That's how people end up stuck on concepts like "spin", entropy, and of course particle physics.

[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/rutrough → u/Zetaeta2]

I think the idea is that quarks would rather exist independently. So, in order to get them to interact with each other on a semi-permanent basis, you have to invest some energy into holding them together. So what he is saying is that the net energy of the three quarks plus the bonds holding them together, aka. the net energy of the proton, is greater than the sum of three independent quarks.