# Chapter 23 The Beginning of Time

When did it all start?   About 14 billion years ago

Extrapolating the Hubble Constant backwards (allowing for acceleration)
Universe is aging -- more distant galaxies look younger

"Big Bang" Theory:
Universe started as small, dense, hot blob of matter and photons
Expanded
Expansion caused cooling: temperature plot

Grand Unified Theory GUT All forces are the same when the energy is high
Inflation -- a sudden expansion of spacetime by a factor of roughly 1030
It flattens our piece of the universe

Outline of the events:
Diagram

Table:

 Time Temp K Event Planck Era 10-43 s 1032 Planck time Gravity separates GUT era:   Gravity + 3 forces 10-38s 1029 Symmetry breaking Strong separates Electroweak era: GUTS Inflation, Quarks + leptons 10-10s 1015 Electroweak separates Particle era: quarks + leptons, four forces 10-3s 1012 Confinement q -> p, n Nucleosynthesis era: p+e  -> n+n p, n -> He plus a little Li  (Start of Standard Big Bang) 5 min 109 nuclear freeze out He/H set Era of nuclei:  H, He, electrons plasma 380,000 yrs 3000 E-M freeze out recombination p+e -> H atom CBR released Era of Atoms 1 billion yrs 30 Protogalaxies condense Era of Galaxies  galaxy formation, etc present CMB at 3

Evidence

Cosmic Microwave Background

H He abundance in Population II stars

Number of neutrons sets amount of H vs. He

Persistent problems

Why is the universe so smooth?  [ to about .01%]

Why is the universe so close to the critical density

Solved by Inflation

Why not perfectly flat?

Quantum fluctuations get ‘inflated’ to be the current size of the lumps

If all this happened we should see the lumps in the CMB and their size should tell us what the density was at that time. (Was it the critical density?)

According to WMAP:

Baryonic matter is 4.4%

Total matter is 27%

Universe age is 13.7 billion years

The Future
An accelerating universe slows down
Eventually, protons decay -- all ordinary matter falls apart
Eventually, even black holes evaporate
Only subatomic particles and photons are left, rattling around the vast spaces of the universe