I'm reading Carroll and Ostlie's "An Introduction to Modern Astrophysics". In the BBN section, they describe that the universe contains a mixture of photons, electron-positron pairs, and electron and muon neutrinos and their antiparticles. They also mention that there was a small number of protons and neutrons and that protons and neutrons were constantly being transformed into each other from various reactions. From my understanding (not C & O necessarily), the Heisenberg Uncertainty Principle permits matter to spontaneously appear because there is some uncertainty as to how much mass there is in a vacuum; however, these particles must appear in "pairs" (ie. positron and an electron). If we assume inflation is correct, it is thought that these particles would become diluted after this process. So I guess I'm wondering how are these particles predicted in general (during the radiation era)? Is the energy released during inflation thought to have created these particles or something else?

  • $\begingroup$ I don’t have the expertise to write a full answer, but basically the energy to create the massive particles is coming from the photons. “Pair production” can produce a particle and its antiparticle from a single photon if that photon has more than the rest-mass energy of the two particles. This creation process competes with processes that destroy particles, like annihilation of matter-antimatter pairs, and photodissociation of any nuclei that form. The net effect of all these processes determines the matter-photon balance at any time. $\endgroup$ Apr 20, 2021 at 12:37
  • $\begingroup$ Thanks. I was reading something about the particles being created from reheating after inflation. Does it have something to do with that? $\endgroup$
    – Astroturf
    Apr 20, 2021 at 14:54


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