Aaron1947 said:
Okay, good, that's what I thought. Does the pauli exclusion principle explain why electrons don't crash into the nucleus?
PS-I'm trying to understand how the elements were formed during the big bang. I understand how the strong interaction formed protons and neutrons, then bound them into nuclei, from the quark-gluon plasma, but what I don't comprehend is how electrons came into existence, or how they ended up orbiting around the nuclei.
1. Short answer to "how electrons came into existence": Nobody really knows.
The term for how electrons came into existence is "leptogenesis". And, the real question the plagues leptogensis, and also the question of how quarks came into existence, which is called "baryogenesis" is how there came to be so many more quarks than anti-quarks, and so many more electrons than positrons in the universe, when all process that we observe today produce new quarks only in quark-antiquark pairs, and new leptons only in lepton-antilepton pairs. (Creating new quark-antiquark pairs, and new lepton-antilepton pairs happens all of the time according to more or less perfectly understood processes in the Standard Model such as W and Z boson decay.)
These processes are also limited by conservation of electric charge, but that is not so problematic, because the net electric charge in the universe is zero or very nearly so.
But, we don't know why there is this matter-antimatter asymmetry. One way to achieve this is to have a process that creates more matter than antimatter, and then you need all the antimatter to annihilate in collisions with matter, so that what is left over being almost all matter. But, no such process has been identified. It also doesn't help that most of the particles in the universe are neutrinos and we don't know the ratio of neutrinos to antineutrinos in the universe because its really hard to tell the difference when measuring them when you don't know their source.
A process that does not conserve the net number of quarks minus antiquarks in the interaction violates conservation of the quantum number B (baryon number). A process that does not conserve the net number of leptons minus antileptons in the interaction violates conservation of the quantum number L (lepton number).
The only violation of independent B and L conservation in the Standard Model involves a hypothetically possible but never observed high energy process called a sphaeleron process in which B-L rather than B and L separately is conserved. But, models of the Big Bang have shown that this process combined with CP violation that is found in the Standard Model (since any process that treats matter and antimatter differently must by CP violating), cannot account for the matter-antimatter asymmetry in the universe if it started at B=0 and L=0 as pure energy. An alternative is that at time zero, both B and L had their current values or something close modified only by sphaeleron processes since then, and that we are simply presumptuous in assuming B=0 and L=0 to be the initial conditions of the universe.
Other processes beyond the Standard Model (because they are prohibited by the Standard Model) that would violate independent conservation of baryon number and lepton number (usually while preserving B-L or B+L) are flavor changing neutral currents and neutrinoless double beta decay. Neither of these phenomena have ever been observed either and have been rigorously ruled out to high precision (although the effort to push that precision greater is ongoing and an important area of investigation). At a minimum, these processes are rare enough that they don't contribute meaningfully to changing matter-antimatter symmetry today and not enough to account for what we observe earlier in the universe.
Presumably, any process that gives rise to baryogenesis or leptogenesis with the observed matter-antimatter asymmetry occurs only in very early parts of the Big Bang-like conditions which is why we don't observe it in nature or in high energy physics experiments today.
2. Electrons end up orbiting around nuclei because nuclei are positively charged and charged leptons that are not antimatter are negatively charged, so they are attracted to each other until they are paired up one proton to one electron. Electromagnetic forces are powerful.
3. I leave to someone else an explanation of why electrons don't crash into the nucleus which I basically understand but I am not very good at explaining succinctly. It is more to do with conservation of momentum and less to do with the Pauli exclusion principle.
