1. Observational Evidence of Creation 1)The sky is dark! (Olber’s Paradox) If the Universe were infinite in space and time, every line of sight would eventually end on a star. Even if it were very far away and faint, that would be made up for by having more of them in a smaller patch of sky. The sky should have the same brightness as the Sun (or at least an M star!). This resolved by the fact that the Universe started a finite amount of time ago (the expansion helps too with the redshift).

2. 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 (actually about 14 billion) and that it started at a set and knowable point of time. The moment of Creation is now an empirical fact.

3. Conceptual Framework for the Big Bang 1)As you run the movie backwards (look back in time), the Universe shrinks and gets hotter. 2)The average photon increases in energy with decreasing time, and the photon density goes up like T 4 (matter density like T 3 ). 3)Energy and mass are equivalent, so they will freely exchange when E average >m particle c 2 for a given particle. 4)The particles created from energy must be equal numbers of matter and antimatter (to conserve all quantum numbers). 5)Once the matter froze out (going forward in time), all the antimatter would annihilate with the matter, leaving energy (which gets redshifted down below the threshold energy to make particles again). Since there is matter now, there must have been a slight overproduction of matter compared with antimatter. This tiny symmetry violation (1 per 100 million) produced all the particles now in the Universe. You can infer that there are 100 million photons for every proton. Where are they…? Energymatter + antimatter Energy

4. 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% He by number or 25% helium 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 of those then determines the amount left today (so we know what it was).

5. The Recombination Era Age of Universe: about 300,000 years The light comes to us from the time when hydrogen atoms were able to recombine and stay that way. The interaction of photons with matter was then restricted to the hydrogen spectral lines, leaving almost all photons free to fly unimpeded. We see such photons redshifted by z=1000 (meaning the Universe was 1000 times smaller at that time).

6. All Around Us – The Fireball

7. The Cosmic Background Radiation Those photons should be all around, but very cool (redshifted). And they are… A perfect blackbody (thermal) spectrum: 2.736 K Cosmic dipole (motion) Penzias & Wilson 1965 (and Dicke) COBE (1990)

8. Imperceptible structure then  galaxies today The fireball had to have some structure, or we wouldn’t have any now. The effort to find it was epic; it was only seen at one part in 100,000. Galactic plane

9. The Formation of Large Scale Structure The Universe hasn’t really been around long enough for the gravity from all the galaxies we see to have caused the collapse of matter into this foamy structure. Computer models show this could only happen if there is a lot more “cold, dark matter”out there – invisible, but dominating the mass in the Universe.

10. Dark Matter - rotation curves Rotation curves imply the mass-to-light ratios of galaxies go up as we look on larger scales: Sun  M/L=1, solar neighborhood  M/L=3, galaxy  M/L=50

11. Dark Matter – cluster speeds galaxy clusters  M/L=200-500 From average speed of galaxies – the cluster would fly apart From X-ray gas held in – several million degrees and extensive

12. Dark Matter :gravitational lensing The mass required to produce the observed lensing is much higher than the luminous mass. This is a direct observation of gravity due to dark matter.

13. What could the dark matter be? 1)Normal but dark matter (“baryonic”) : rocks, white or brown dwarfs? 2) Black holes or neutron stars? Too much metals would have been produced. Anyway, Big Bang nucleosynthesis tell us this can’t be it…

14. WIMPS and Cold Dark Matter Could dark matter be some kind of new particles which interact very weakly with matter (like neutrinos do) but massive, and not moving relativistically? Experiments at Berkeley and elsewhere are looking for them (guaranteed Nobel prize!).

15. A Brief History of Time

16. The Horizon Sets the Limit of the Observable Universe 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).

17. 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.

18. 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?

19. The Solution : Inflation!

20. 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  =0.25. Where’s the other 0.7?

21. 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 really is flat or doing something else. Type I supernovae provide such an opportunity…

22. 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.

23. A Major Surprise! Something is giving us a push… A very Berkeley project…

24. W-MAP A detailed view of the cosmic fireball. Results: The Universe is 13.7+/-0.2 billion years old. The curvature of observable spacetime is flat. Galaxies began to form after 200 million yrs.

25. 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 results of Big Bang nucleosynthesis shows that matter of all forms 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. The rest appears to be in the form of “dark energy” (eh???) What’s in the Universe: VACUUM (with dark energy) 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

26. 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)

27. 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)