1. The Big Bang and the Expansion of the Universe

2. What is the Big Bang?
It was not a “bang”, this name came about by accident
The universe started out as a super hot, infinitely dense point
Rapid expansion started and after a while, matter started clumping together and stars were born.

3. Time: < 10-43 sec Temp: > 1032 K
Planck Era
Time: < sec Temp: > K
No theory of quantum gravity
All forces may have been unified
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4. Time: < 10-37 sec Temp: > 1032 K
Inflationary Period
Time: < sec Temp: > K
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5. Time: 380,000 years–1 billion years Temp: 3,000–20 K
Era of Atoms
Time: 380,000 years–1 billion years
Temp: 3,000–20 K
Atoms formed at age
~380,000 years.
Background radiation is released. Universe becomes transparent.
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6. Time: ~1 billion years– present Temp: 20–3 K
Era of Galaxies
Time: ~1 billion years– present
Temp: 20–3 K
The first stars and galaxies formed by
~1 billion years after the Big Bang.
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7. Inflationary period 10^-37 to 10^-35 seconds
Doubling every 10^-60 seconds Expanding faster than the speed of light!
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8. Tuesday, December 4, 12

9. Evidences of the Big Bang
1. The universe is expanding- All galaxies are moving away from each other. The space in between galaxies is expanding.
Not only is the space in between galaxies expanding, but the rate of expansion is accelerating.
2. The abundance of elements- By running simulations of the big bang on computers, the abundance of H and He match what we actually measure.
74% Hydrogen
25% Helium
3. Cosmic background radiation- This is the leftover energy from the Big Bang. Conditions were very hot and that heat energy is spread throughout the universe equally.