1. Observational Evidence of Creation 2) The Universe is observed to be expanding (so in the past it was smaller). The Steady State Universe tried to get around this by supposing that new galaxies appear out of nowhere to fill the increasing volume (no more unreasonable than supposing that the Universe appeared). But then the past shouldn’t look different than the present (on average) 3) The Universe was hot and opaque in the distant past. This is proven by the thermal cosmic background radiation. Only if all space were opaque would all space be filled with thermal photons (and their current temperature is reasonable given the expansion factor) 4) A theory which supposes the Universe evolves in this way can predict how the composition of the Universe arose from the primordial fireball. These predictions are borne out well by the current observed composition. It seems inescapable that the Universe is only 10-20 billion years old, and that it started at a set and knowable point of time. The moment of Creation is now an empirical fact.

2. Big Bang Nucleosynthesis From t=1-200 sec the Universe had about the density of water and a temperature of about a billion degrees. Protons and neutrons froze out of the radiation field (fewer neutrons because they are a little more massive), and neutrons began to decay. There were 14 protons for 2 neutrons. The neutrons fused to make deuterium, and then helium. This left 12 protons and 1 helium (He 4 ), or about 8% Helium by number and 25% by mass. Just as we see everywhere today! A little bit of deuterium and lithium was also left, and we see that too. The exact density back then determines the amount left today (so we know what fraction of critical it was).

3. Density and Composition of the Universe Based on what we can see, stars fall short of providing the critical density by a factor of 200. Neutrinos don’t seem to help. Indeed, the fraction of helium observed implies that matter is a factor of 20 short. But there are good theoretical reasons to believe the curvature is flat. Dark matter provides about a third of what is needed. What’s in the Universe: VACUUM Counting particles in 100 sq meters 1 heavy (more than O) atom 100 atoms of C,N,O 100,000 atoms of helium 1,000,000 atoms of hydrogen 30 times that mass in dark matter (particles of unknown mass)? 100,000,000,000,000 cosmic photons and as many cosmic neutrinos

4. A Brief History of Time

5. The Horizon Problem 14 billion light years 28 billion light years The observable Universe has a horizon (in light years) set by its age. Each point has the same size horizon. Not only has light beyond the horizon not had enough time to reach us, but the redshift at the horizon is infinite. This is an event horizon (like a black hole’s).

6. Mysteries in the Big Bang Theory The Horizon Problem –The cosmic background in all directions has the same temperature, yet opposite sides of the sky are not in “causal contact” (they are outside each other’s horizons). The largest COBE structures are also larger than their own horizons! The Flatness Problem –The geometry of the Universe now appears to be flat. But it has expanded by a factor of 10 60, so at the beginning it had to be flat to within a factor of 10 -60 ! And yet it had to have enough density fluctuations to produce today’s structure. How was that arranged? The Matter Problem –Matter and antimatter should be created in exactly equal amounts, but they weren’t (by a tiny bit). The Creation Problem –How did spacetime suddenly spring into being, with lots of mass and energy, and violently expand?

7. The Solution : Inflation!

8. The Flatness Problem Solved Geometrically, it is easy to see how inflation can remove any initial curvature to spacetime (at least within the horizon). But remember that the geometry of spacetime is tied up with the density of the Universe. We call this  (Omega) and set it equal to 1 if it has the critical value. If inflation is correct, then we must have  =1, and the question becomes: how is that accomplished? We know that matter can only supply  =0.05, and dark matter gives about  =0.3. Where’s the other 0.65?

9. Determining the geometry (fate) of the Universe The MAP mission. Boomerang

10. Cosmic Microwave Background Anisotropy spectrum The details of the features on the fireball (CMB) tell us what the curvature of spacetime is. They confirm that it is flat, which means the Universe will not recollapse, but will expand forever.

11. Another measure of curvature If we have an independent way of getting distances to very distant objects, we could try to measure the change in the Hubble constant with time, and get the behavior of the scale in the distant past. Then we’d know which curve we are on, and whether the Universe is flat or doing something else. Type I supernovae provide such an opportunity…

12. Exploding White Dwarfs as “Standard candles” We need to find them very far away, but be able to distinguish them from the light of the host galaxy.

13. Using Supernovae for Cosmology Then we must measure their “Type I” spectrum, and follow their brightness history. Finally, we must prove they really have a standard brightness (and dust isn’t a problem). A very Berkeley project Keck data

14. A Major Surprise!

15. Something is giving us a push… It’s not due to dust…

16. Astro Quiz The worst part about the accelerating expanding Universe is: 1)It means this must be the only Universe (no recollapse). 2)It means that everything will eventually freeze and fade away (as the cosmic background is doing). The average temperature has already fallen to 3 degrees absolute. 3)It means that the contents of the observable Universe are actually diminishing with time, as stuff accelerates out over our horizon. Eventually there won’t be much to see outside our locally bound region of space.

17. Dark Matter and Dark Energy Supernovae taken with the CMB anisotropies constrain us to a Universe in which the flatness is confirmed, but 2/3 due to “dark energy” which is currently accelerating the expansion of spacetime. This may be related to the original cause of inflation, or be a “cosmological constant”. It would be a form of “vacuum energy” (like an anti-gravity). We do not know how to calculate it at the moment (off by 10 120 – the single worst #!). Einstein had put such a force in his equations to keep the Universe static. When Hubble found it was expanding, Einstein said adding the force was his “biggest blunder”. It turns out, saying that may have been his biggest blunder!

18. Solutions in the Big Bang Inflationary Theory The Horizon Problem –Everything in the observable Universe (and well beyond) was within the horizon before inflation. The Flatness Problem –Inflation was so extreme that all initial conditions are erased, and Omega must now be exactly 1. The Matter Problem –Grand Unified theories show how excess matter can be produced (and symmetry violations have been observed in particle accelerators). The Creation Problem –A quantum fluctuation in the “false vacuum” led to a phase change, and imposed quantum fluctuations in spacetime which led to the observed structure

19. What Causes Inflation? A super-symmetric “false vacuum” goes through a phase transition into vacuum energy and mass-energy. The net energy is zero before and zero after (gravitational potential is a negative term).

20. Multiple Universe(s) This general picture allows for our Universe to keep branching, or for other Universes to be created within it (though of course there are no connections in spacetime between these Universes.

21. The History and Fate of the Universe Primordial Era t = -50: Planck epoch t = -35: symmetry breaking, inflation t = -12: formation of “normal” particles t = -6 : production of helium t = 4 : end of radiation domination t = 5.5: atoms form, cosmic microwave background Stellar Era t = 7 : first stars form t = 9 : Milky Way, galaxies form t = 9.5: formation of solar system t =10.2: Sun dies t = 14 : end of star formation, smallest stars die Define time by “cosmic decade”: time=10 t years (t is decade)

22. The History and Fate of the Universe Degenerate Era t = 16 : colliding brown dwarfs t = 19 : most brown dwarfs, planets ejected t = 30 : remaining dwarfs fall into central black hole t = 37 : free protons decay, neutron stars decay t = 39 : protons in dwarfs and planets decay Black Hole Era t = 42 : dark matter particles decay into photons t = 66 : stellar black holes evaporate t = 84 : galactic black holes evaporate t = 98 : cluster black holes evaporate t = 141 : last positronium decays (see “The Five Ages of the Universe” by Adams and Laughlin) Define time by “cosmic decade”: time=10 t years (t is decade)