2 ms·

It gets a bit more complicated than that. Matt Strassler has a couple relevant articles on his blog site. The first goes deeper than the 3-quark simplificatio

It gets a bit more complicated than that. Matt Strassler has a couple relevant articles on his blog site. The first goes deeper than the 3-quark simplification. "What's a proton? First and foremost, it’s a mess. A total mess" http://profmattstrassler.com/articles-and-posts/largehadroncolliderfaq/whats-a-proton-anyway/ http://profmattstrassler.com/articles-and-posts/largehadronc... The second digs into both protons and neutrons "So there are reasons to go further and describe things as I have elsewhere on this website: a proton is made from three quarks (two up quarks and a down quark), lots of gluons, and lots of quark-antiquark pairs (mostly up quarks and down quarks, but also even a few strange quarks); they are all flying around at very high speed (approaching or at the speed of light); and the whole collection is held together by the strong nuclear force" http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ http://profmattstrassler.com/articles-and-posts/particle-phy... And the third deals with neutron stability in nuclei, and specifically focuses on the stability of the neutron inside a deuteron. http://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/the-energy-that-holds-things-together/neutron-stability-in-atomic-nuclei/ http://profmattstrassler.com/articles-and-posts/particle-phy... [forgive me for combining a reply to an earlier comment you made on neutron stars] We don't know the equation of state of a neutron star; most viable models have substantial layering and an impressively busy energy-density flow. Most models predict neutron stars to be very bright in neutrinos, although the brightness is typically greatest at the outer layers rather than from the deeper ones where one would expect a superfluid sea of degenerate neutrons to dominate almost to the exclusion of everything else (e.g. there may be small numbers of superconducting protons floating around in it), and mechanisms which produce the Pauli Exclusion Principle are non-negligible. Possible mechanisms are somewhat constrained. How the density profile goes below the superfluid layer is I think mainly speculation; there are BH-remnant-related reasons to hope for a lattice crystal or some block-like structure of subatomic particles forming an inner core. JM Lattimer has a recent (2013) paper: http://arxiv.org/abs/1305.3510 http://arxiv.org/abs/1305.3510

Manishearth 11y ago
> the whole collection is held together by the strong nuclear force to be pedantic, the "lots of gluons and q-antiq pairs" is the strong nuclear force in action Also, you're talking about virtual particles here, it's acceptable to (and usually this is done) ignore them when describing the "contents" of a particle since they're everywhere (in less concentration perhaps) anyway. But yeah, those particles are there.
- raattgift 11y ago
  I'm not sure what you mean by "they're everywhere (in less concentration perhaps)". There's no antiquark in the usual three-quark simplified description of a proton, yet without antiquarks how does one explain the charged leptons and anti-leptons readily observed following high-energy proton collisions? Are we dancing around a question like, "what really happens close to the IR fixed point"?
  - qubex 11y ago
    I think he means that the attendant “background noise” of virtual particles occurs within the notional radius of the compound proton just as they occur within any other volume of space.
  - Manishearth 11y ago
    I'm saying that these quarks are not long-lived, they come and go like other virtual particles. You have this behavior outside of a hadron too, just that you're more likely to see a quark-antiquark pair inside a hadron than outside. The sea quarks within the hadron are still virtual particles, though. And often virtual particles aren't considered to be there at all, after all, from that logic one might say that a proton contains all particles (it does, since there always is a possibility of a virtual particle pair of any type springing up). Of course, the possibility of the quarks coming up is more likely since they can be obtained from a gluon, but they're still virtual. We're just dancing around the question "should we count virtual particles when talking about the contents?". The answer usually depends on context. So it's completely ok to say that a proton is just three quarks, since those are the only real particles in it.
elbigbad 11y ago
The Strassler links are VERY good, thank you for posting. I'm especially impressed that he answers comments on the posts in detail, even "stupid" questions.
- raattgift 11y ago
  I agree, Matt Strassler is a gifted communicator. It's a tragedy that he has left full-time theoretical physics for greener pastures as a result of the huge (as in double-digit percentages, and in some cases more than a third) cuts in research budgets in the USA, coupled with his desire to remain working in the States. Unfortunately there are quite a few good working-scientist bloggers who have been producing much reduced output as a result of lower funding in general. Some have moved out of the USA and continue to blog. Some have had to focus themselves on earning survival income by pushing out many grant proposals in hopes of even partial funding, and simply cannot afford to take the time to explain other scientsists' work to non-scientists. Some have, alas, mostly stopped blogging altogether.

Manishearth 11y ago

> the whole collection is held together by the strong nuclear force to be pedantic, the "lots of gluons and q-antiq pairs" is the strong nuclear force in action Also, you're talking about virtual particles here, it's acceptable to (and usually this is done) ignore them when describing the "contents" of a particle since they're everywhere (in less concentration perhaps) anyway. But yeah, those particles are there.

raattgift 11y ago
I'm not sure what you mean by "they're everywhere (in less concentration perhaps)". There's no antiquark in the usual three-quark simplified description of a proton, yet without antiquarks how does one explain the charged leptons and anti-leptons readily observed following high-energy proton collisions? Are we dancing around a question like, "what really happens close to the IR fixed point"?
- qubex 11y ago
  I think he means that the attendant “background noise” of virtual particles occurs within the notional radius of the compound proton just as they occur within any other volume of space.
- Manishearth 11y ago
  I'm saying that these quarks are not long-lived, they come and go like other virtual particles. You have this behavior outside of a hadron too, just that you're more likely to see a quark-antiquark pair inside a hadron than outside. The sea quarks within the hadron are still virtual particles, though. And often virtual particles aren't considered to be there at all, after all, from that logic one might say that a proton contains all particles (it does, since there always is a possibility of a virtual particle pair of any type springing up). Of course, the possibility of the quarks coming up is more likely since they can be obtained from a gluon, but they're still virtual. We're just dancing around the question "should we count virtual particles when talking about the contents?". The answer usually depends on context. So it's completely ok to say that a proton is just three quarks, since those are the only real particles in it.

elbigbad 11y ago

The Strassler links are VERY good, thank you for posting. I'm especially impressed that he answers comments on the posts in detail, even "stupid" questions.

raattgift 11y ago
I agree, Matt Strassler is a gifted communicator. It's a tragedy that he has left full-time theoretical physics for greener pastures as a result of the huge (as in double-digit percentages, and in some cases more than a third) cuts in research budgets in the USA, coupled with his desire to remain working in the States. Unfortunately there are quite a few good working-scientist bloggers who have been producing much reduced output as a result of lower funding in general. Some have moved out of the USA and continue to blog. Some have had to focus themselves on earning survival income by pushing out many grant proposals in hopes of even partial funding, and simply cannot afford to take the time to explain other scientsists' work to non-scientists. Some have, alas, mostly stopped blogging altogether.