ASTR 340 Lecture Notes - Lecture 15: Nucleosynthesis, Big Bang, Isotropy
Document Summary
Cosmic microwave background: evidence for homogeneity and isotropy. As universe expands, physical density of any set of particles decreases, because space in between decreases. Matter stays the same but volume increases. In reference to light, must consider redshift to calculate energy density. Particle physics: strong nuclear force: force carriers: bosons. If protons have enough energy, they interact and produce particles and anti-particles. P=critical density of the universe which tells us its fate. Electron pairs, equilibrium reactions between protons/neutrons: neutrino + proton = anti electron + neutron, neutrino + neutron = proton + electron. Ended when temperature cooled and fell below threshold temp for electrons. Nucleosynthesis: primordial: big bang (first 20 mins) stellar: in the cores of stars t~180 s (3min): primordial nucleosynthesis neutrons, protons, electrons, protons, etc. Stability gap: no stable nuclei with masses of 5 or 8. Once universe reaches stability gap, pn stops (1000s, or 20 min)
