Background radiation (light) from Big Bang (visible) freely streaming from universe since atoms formed at temperature ~ 3,000 K (cf. sun = 6000 K)

using oldest light in the sky, extrapolate from infant universe to today NASA - WILKENSON MICROWAVE ANISOTROPY PROBE

…4 scenarios for evolution of universe… Friedmann’s General Relativity solutions depend upon total mass of universe (+ any cosmological constant = dark energy =energy of the vacuum)

Grand Unification Era from Planck time (~ sec) to end of GUT force (~ sec) strong interaction distinct from others history of the universe?

Electroweak Era from end of GUT force (~ sec) to end of electroweak force (~ sec) …studied at accelerators

Particle Era matter ~ antimatter ~1 extra proton for every 10 9 proton-antiproton pairs!

Era of Nucleo- synthesis matter annihilates remaining antimatter at ~ sec old 2 protons + 2 neutrons fuse making helium nuclei …1 st 3 minutes

Era of Nuclei deuterium & helium nuclei form at age ~ 3 minutes Universe now too cool to blast helium nuclei apart

Era of Atoms atoms form at age ~380,000 years big bang light liberated …free flowing until our epoch

Era of Galaxies galaxies form at ~ 1 billion years

RESERVE

Amount of dark matter is ~25% of the critical density suggesting fate is eternal expansion Not enough dark matter

But expansion appears to be speeding up! Not enough dark matter Dark Energy?