In The Beginning…

1. In The Beginning…

3. We can talk about time since the Big Bang, the temperature of the Universe, and the average particle energy interchangeably. • In the beginning, universe is very hot • As time proceeds, the universe expands, and temperatures/energies drop.

4. Planck Era (t < 10-43 s) Quantum fluctuations in spacetime break GR. Need quantum gravity (or string theory) to understand this. So far, we don’t really know what happens during this era.

5. GUT Era (10-43 - 10-35 s) GUT force Grand Unified Theory (GUT) force combines 3 of 4 forces. Inflation is thought to happen in GUT era (maybe when the strong force separates out)

6. Inflation (Dark Energy on steroids) • Universe expands by a factor 1030 in 10-36 seconds. • Size of atom to bigger than a galaxy. • Prior to Inflation, the entire observable universe (today) was about the size of a grapefruit. • Theory invented to explain 3 problems with the universe: • Where does structure come from? • Why is the universe so uniform? (Horizon Problem) • Why are we so close to the critical density? (Flatness Problem)

7. Where does structure come from? Quantum fluctuations (tiny) Seeds of structure formation Initial fluctuations put in place by Heisenberg Uncertainty Principle get magnified to size needed to form large scale structure

8. Why is the universe so uniform? (Horizon Problem)

9. Why is the universe so uniform? (Horizon Problem) CMB is uniform to 10 parts per million over the entire sky. Snapshot of the universe at t=380,000 years Point A: T = 2.71964 K Point B: T = 2.71963 K Points A and B are on opposite sides of universe, yet are able to equalize their temperature in only 380,000 years What speed does this imply? V = D / t = 14 million ly / 380,000 years = 37 x speed of light

10. Why is the universe so uniform? (Horizon Problem)

11. Why is the Universe flat?

12. The fact that the Universe is flat means we are at the critical (energy) density. • If the universe is closed, the mutual gravitational attraction of the ‘stuff’ within the universe will cause it to collapse again. • If the expansion is fast enough, gravity can’t overcome it, and it keeps expanding forever. (open universe) • If the universe is flat, it has just enough energy to keep expanding forever without collapsing again.

13. The fact that the Universe is flat means we are at the critical density. There may have been curvature before inflation. By increasing the size of the universe, this gets smoothed out. Only noticeable on scales bigger than observable universe This is because the expansion happens so fast that light can’t keep up.

14. inflation

15. Electroweak Era EM and weak forces become distinct at 10-10 s. This is the closest energy to the big bang we’ve ever been able to make in a lab. Got Weinberg his Nobel Prize in 1979

16. Particle Era • Beginning of Particle Era: • So hot that energy turns into particles (matter, antimatter, WIMPs) • End of Particle Era: • No longer hot enough to convert energy to particles (1 millisecond) • Slightly more matter than antimatter for some reason

17. Nucleosynthesis Era • Beginning of nucleosynthesis era: • Balance between photons (break up nuclei) and fusion (build bigger nuclei) • One big fusion reactor • End of nucleosynthesis era: (3 minutes after big bang) • H, He, D, Li • Too cold for fusion to make bigger nuclei • Too cold for photons to destroy nuclei

18. Era of Nuclei Pretty boring time. 3 minutes after BB to 380,000 years • Beginning of nuclei era: • H, He, D, Li, + electrons floating around • Too hot to form atoms • Matter and radiation coupled because free electrons stop photons from going very far • End of nuclei era: (RECOMBINATION) • Universe has cooled to the point where you can form atoms • Atoms quickly steal all the electrons and light is free to travel

19. Recombination CMB is where recombination occurred. The light we see is from the first photons that were able to escape once the universe recombined 380,000 years after the big bang. This is the farthest back in time we can “see”