PHYS 037 Lecture Notes - Lecture 4: Cosmic Neutrino Background, Deuterium, Weak Interaction
18 Oct 2016
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Universe expanded and cooled down when density of material and intense heat caused fusion of elementary particles to form nuclei of light chemical elements. Reached temp that was no longer enough for elements heavier than. Whatever light elements are present in the universe are left over from the big. Rate of weak interaction was enough to keep particles in equilibrium. Rate of weak interaction between neutrinos & electromagnetic eld slowed. Emergence of a neutrino background in the universe. For every 1 neutron, there were 6 protons. When temp of universe reached below 8 x 10^8 k at 1-2 min after the big bang. Fragile & would be destroyed by energetic photons. Results in ^4he with 2 protons & 2 neutrons. There were only protons and electrons after the big bang https://emailucr-my. sharepoint. com/personal/nyree_catlin_email_ucr_edu/_layouts/15/wopiframe. aspx?sourcedoc={c82d6fc0-8c22-4d0b-9da7-2a2b2b3a1269}&acti After the big bang, temp & density became high enough for deuterium (heavy hydrogen) to form by fusion. Bbt predicts 24% of matter in early universe was helium.
