So, I have been reading about connection of particle physics and thermodynamics of early universe. Like after big bang, and quark - gluon plasma etc..

Anyway, after 1 second after big bang, the ratio of proton and neutron was around 7; which means there were a lot of more protons, rather then neutrons.

And this is also a reason which helped later nucleosynthesis. So, my question is what are the reasons here why there was a bigger number of protons, from neutrons.

Should I watch it here from the perspective are protons and neutrons stable? Is the same like radioactive decays?

  • $\begingroup$ stephen weinberg's book The First Three Minutes deals with this in detail and is highly recommended. $\endgroup$ – niels nielsen Jul 19 '19 at 3:51

It takes more energy to create a neutron than a proton. but some of the protons were transformed into neutrons later on. The proton is a stable particle and never decays, despite some rumours to the contrary, but the neutron is unstable outside the nucleus and decays with a half life of about 10.5 minutes. However, on the timescale you refer to in your question, hardly any would have had time to decay. For every matter particle created, there should have been an antimatter particle, for every proton an antiproton, every neutron an anti-neutron, and for every electron a positron. The great mystery is: where did all the antimatter go? One or two attempts have been made to explain this, but they are not very convincing.

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