Creation of matter in the big bang

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Hi,

http://curious.astro.cornell.edu/ab...matter-in-the-universe-come-from-intermediate

The website given above says that the matter was created via pair production process (like electron anti-electron creation) in the big bang. However, the linear momentum has to be conserved in the pair production. Therefore, you will need an electric field of a nucleus.

If you did not have nuclei how could matter was created via pair production in the big bang?

Thank you in advance.
 

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However, the linear momentum has to be conserved in the pair production. Therefore, you will need an electric field of a nucleus.
That only applies to pair production based on a single high energy photon. It doesn't apply to pair production from the collision of two particles, for example. At the densities of the early universe even photon-photon collisions were frequent enough to matter, and there were many other particles around to serve as collision partners. You don't need a nucleus. Nuclei are just the most relevant collision partners in today's universe.
 
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PeterDonis
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The website given above says that the matter was created via pair production process (like electron anti-electron creation) in the big bang.
I don't think "creation" is correct here. The website says "in the beginning, there was not yet any matter". I don't think that's correct; from what I understand, all of the Standard Model fields had a lot of energy pumped into them in the "reheating" event at the end of inflation. So there would have been electrons and positrons, quarks and antiquarks, etc. as well as photons.

From what I understand, the reason pair production reactions are important in the early universe is that, without them, all of the electron-positron, quark-antiquark, etc. pairs that were formed in the "reheating" event at the end of inflation would have annihilated each other almost immediately thereafter, so that there would only have been the tiny excess of matter over antimatter that we now have almost from the start of the Big Bang (i.e., the end of inflation). Pair production reactions at the high temperature of the early universe kept re-forming electron-positron, quark-antiquark, etc. pairs as fast as they were annihilated; not until the temperature fell below the threshold temperature for pair production did all of the pairs of particular types (electron-positron, quark-antiquark, etc.) annihilate each other for good, leaving only the tiny excess of matter over antimatter that we have now. (Each of the types has a different threshold temperature because of its different rest mass, so these final annihilation events happened at different times in the early universe.)
 

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