We are told by cosmologists that the universe was dominated by quarks and photons up until one microsecond. Then the quarks formed protons, neutrons, and mesons, and electrons and neutrinos appeared. Now why were the electrons and so forth not there before? Where can I find a fairly technical answer?
The reason is simply temperature. Up until that point, the expanding young universe was just too hot. Collisons between forming particles were so highly energetic, that quarks were ripped free from one another, so that any particles formed from groups of quarks, like electrons and neutrinos, couldn’t exist for any significant length of time.
Wasn’t the ‘universe’ plasma-ish at this ‘point’, and once it got to a stage where electrons could outnumber positrons, conditions were ‘right’ for the continuation.
So, the fact that we are here demonstrates that.
Or something like that.
Protons and Neutrons are made of quarks. Electrons and neutrinos are not made of quarks.
I think the answer to the OP is that at high enough energies, quarks, electrons, and neutrinos are indistinguishable, but I’m not sure.
I wish I had seen this thread earlier, because I hate to miss an opportunity to correct Q.E.D.
But yeah, electrons aren’t made up of quarks, or any other particles for that matter. They’re elmentary. And DrMatrix’s idea about high-energy symmetry may have something to do with it.
Where’s Chronos when you need him?
Go back early enough and any type of elementary particle - quarks, electrons, neutrinos etc., but not nucleons or mesons - will be present in large numbers. Temperatures in the plasma are high enough that any particle in it has enough energy to create particle-antiparticle pairs of any other type. Thus you’ll have quark-antiquark and electron-positron pairs popping up all over the place. But the densities are sufficiently great that any particle is almost instantly annihilated by an antiparticle. One thus has lots of both quarks and electrons kicking around, but individual ones don’t last very long.
As the universe expands, the temperature is dropping. A lot of different things happen together at about 10[sup]-7[/sup] seconds. One is that it’s become sufficiently cool that nucleons and antinucleons can form out of the quarks and antiquarks. By 10[sup]-4[/sup] seconds the outcome is that all the antinucleons have been annihilated and there are just nucleons left.
But the temperature is still sufficiently high that electron-positron pairs are still being produced as before. At this stage, there are thus long-lived protons and lots of short-lived electrons. In fact, on average there are lots more electrons about compared to protons. There’s just this immense turnover of them as they are still being created and annihilated.
Finally, at about 1 second, the temperature drops to the point where electron-positron pairs are no longer being created. They can still annihilate each other, so most of the electrons and all of the positrons are quickly eliminated.
The SDMB, of course.
There are two things you could be thinking of here.
Firstly, when the energies involved are high compared to the masses of both electrons and quarks, the cross-sections for pair production all become roughly the same. Similarly for the annihilation processes. Everything is effectively just massless. That greatly simplifies the thermodynamics.
More fundamentally, however, once you get to GUT energy scales then quarks and leptons start behaving even more similarly. All their interactions (except for gravity) become closely related and they’re all just varients of a much smaller set of particles. The distinction between quarks and leptons disappears entirely. This however only applies in a period much earlier than the OP is asking about.