Upgrade your account to a Community Supporter account and remove most of the site ads.

Reply to thread

Message: <blockquote data-quote="freyar" data-source="post: 6691127" data-attributes="member: 40227">For quarks, up/down, charm/strange, and top/bottom are sort of like "weak force charges" for quarks (very very roughly, think of the first of the pair having one charge and the second a different charge), though it's somewhat more complicated than that.  But the weak nuclear force is extremely short range and can't really reach even across a nucleus very well.  To understand the binding of a nucleus, we need to talk about the strong nuclear force.  First off, protons and neutrons are made of fundamental particles called quarks.  Quarks carry "strong force charge" known as color.  There are three colors (red, green, and blue) for quarks (anti-quarks have anti-colors, which you might call cyan, magenta, and yellow or less imaginatively anti-red, etc).  The strong force is actually strong enough that you can't have a colored object like a quark sitting around by itself.  If you tried to pull the quarks of a proton apart (by, for example smashing the proton with something), the energy you'd need to do that would actually be sufficient to produce (lots of) quark/antiquark pairs from the vacuum, which would the assemble with the original quarks from the proton.  So, in the end, every particle we see on it's own is color-neutral: you can either have a quark/antiquark bound together (so it would have a color plus the corresponding anti-color, which adds to no color) or three quarks with one red, one green, one blue so the colors add to "white."  Quark/antiquark states are called mesons and include the pions I mentioned earlier, and the three-quark states, including protons and neutrons, are baryons.  Together, mesons and baryons are called hadrons, as Umbran already said.  Short version: the quarks in protons and neutrons are held together by the strong force, and protons and neutrons are therefore strong-force-neutral.But even though protons and neutrons don't carry color, the strong force still holds them together.  The analogy is the van der Waals force between electrically neutral atoms: if two atoms are close together, the electrons and nuclei inside can move around so there is a net attraction between the atoms.  It's much much more complicated (to the point where we don't have a good way to calculate it from first principles), but protons and neutrons in a nucleus are held together by the strong force version of the van der Waals force.  And, yes, that is strong enough to overcome the electromagnetic repulsion among the protons (which all have the same electric charge).  Last note: there have also recently been discoveries of 4-quark and 5-quark bound states (tetraquarks and pentaquarks) but not a lot is known about them yet.  Tetraquarks have two quarks and two antiquarks; pentaquarks have 4 quarks and one antiquark.  The question is whether they are one big blob of quarks or something like a meson orbiting another meson/baryon.  These qre quite unstable, though.</blockquote>

Verification