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human
Did all neutrons arise from the Big Bang?

As I understand it, all Hydrogen atoms were created directly at the time of the Big Bang. However, most hydrogen is comprised of a single proton and single electron.

I read that there is a variation on Hydrogen, which contains 1 proton, 1 neutron and 1 electron, but that is far less common as the "no-neutron" version.

All the Helium in the universe was created just after the Big Bang, in the first few minutes as I understand it, but only by *fusion of existing Hydrogen atoms* - they weren't created directly from the Big Bang.

So, given that most of the Hydrogen created had no neutrons (just a single proton), it seems to follow that a far greater number of protons were created than neutrons, at the instant of the Big Bang.

If this is correct, and all the Helium in the universe was created in the first minutes following the Big Bang, and Helium requires neutrons, how are there enough neutrons in the universe to create all the other elements?  Every heavier element seems to require as many neutrons as protons, so I'm not sure how that works, assuming far less neutrons than protons were originally created?

(ed spelling)
gpt
>Did all neutrons arise from the Big Bang?

Not really, no, because most neutrons have been created in stars due to the high density, and some have been created in tiny amounts through other beta-decay processes.  However, many neutrons did arise from the big bang.

>I read that there is a variation on Hydrogen, which contains 1 proton, 1 neutron and 1 electron, but that is far less common as the "no-neutron" version.

Yes -- this isotope of hydrogen is known as "deuterium," also called heavy hydrogen.  There is also an isotope called "tritium" (1 proton, 2 neutrons, 1 electron), but unlike deuterium it is unstable.

>So, given that most of the Hydrogen created had no neutrons (just a single proton), it seems to follow that a far greater number of protons were created than neutrons, at the instant of the Big Bang.

Yes, this is correct.  The ratio was approximately 7 protons for every 1 neutron -- or equivalently, 1 helium atom for every 12 hydrogen atoms, which is 75% hydrogen and 25% helium (by mass).

>If this is correct, and all the Helium in the universe was created in the first minutes following the Big Bang, and Helium requires neutrons, how are there enough neutrons in the universe to create all the other elements?

Because neutrons are created during the fusion processes within stars.  Protons beta-decay into neutrons when enough energy is present for the process to be allowed -- this results in hydrogen (all protons) being converted into deuterium/helium (both protons and neutrons).  This is why the densest stars (neutron stars) are composed almost entirely of neutrons; the extreme pressure causes electrons to be captured by protons, and neutrons to be created.

So after the big bang, there were only enough neutrons to form a little bit of helium, and the stars and early supernovae were responsible for creating the rest of the heavy elements through fusion processes.

Hope that helps!