1. COSMOLOGY HOW IT BEGAN Chris Impey University of Arizona

2. Norton, 2010 2

3. Science is Seeing Space 3

4. A Scale Model Set the Earth to the size of a walnut, or a 1:500,000,000 scale model = The Moon is a pea at arm’s length The Sun is a 3 m ball 300 m away Neptune is a softball 9 km away Nearest star is 80,000 km away

5. The Moon is a seconds walk away The Sun is 8 minutes walk away 10 hours to walk the Solar System 4 years to walk to the nearest star And at this scale, light is reduced to very slow walking speed. There’s no way information in the universe can travel any faster

6. Reduce the scale by a factor of 10,000,000 The Solar System is a grain of sand The distance between stars is 20 m The Milky Way is the size of the U.S. The MW has 400,000,000,000 stars

7. Now reduce by another factor of 10,000,000 The Milky Way is like a small plate The nearest galaxy is 5 m away The universe is the size a large city Billions of galaxies within this space

8. The Contents 8

9. Scattered in a universe 46 billion light years across Galaxies 9

10. The Milky Way is typical with 400 billion stars Stars 10

11. Almost all the simple elements hydrogen and helium Atoms 10 80 11

12. A billion photons for every particle Photons 10 89 12

13. Mediocrity We therefore live on an: Average planet around An average star in an Average galaxy in a Very large universe Copernicus 13

14. Composition of the Universe Dark matter: 22% Dark energy: 73% Universal Pie 14

15. Cosmology 15

16. Cosmology Slipher 16

17. Lookback Time If the speed of light were infinite, light from everywhere in the universe would reach us at exactly the same time and we would see the entire universe as it is now. But it is not, so we see distant regions as they were in the past. 17

18. Cosmology: What We Know 1.Redshift – it’s a universal expansion of space-time, not a Doppler shift. 2.The microwave background radiation (CMB), a signal that is close to perfectly thermal, at temp of 2.726K. 3C 273 18

19. 3.Deuterium and Helium synthesized (much higher temperatures in the past ). Hubble Ultra Deep Field HSTACS 4.Galaxies in past look younger (smaller and more irregular). 19

20. Big Bang 19

21. A good scientific model should always make predictions which can be verified. The big bang model makes two predictions which have been verified since the 1960s: the existence and characteristics of the cosmic microwave background (CMB) the expected Helium abundance in the Universe The model predictions agree with all current observations. There is much indirect evidence the universe was smaller and hotter in the past Evidence 21

22. Cosmic Microwave Background The universe is immersed in a sea of radiation. 380,000 years after the big bang, the universe had cooled enough for free electrons to become bound into atoms of Hydrogen and Helium Without electrons to scatter them, photons were able to travel unhindered throughout the universe The universe became transparent The temperature of the universe was 3,000 K at this time, similar to a stellar photosphere It has expanded by a factor of 1000 since then, reducing the temperature to 3000/1000 = 3 Kelvin 22

23. When we look at the CMB, we look at the surface of the glowing “fog” that filled the entire early universe! anything The CMB has highest redshift of anything we can see (z = 1000). 23

24. 24

25. 1% of the specks on any TV tuned between stations are interactions with the big bang 25

26. Science is Seeing Origin 26

27. The big bang was extraordinary― the instantaneous creation of all of space and time, containing energy to drive the expansion and enough matter for 100 billion galaxies. The initial state was so compact that it can only be described by a theory that unites gravity and the quantum world. We do not have such a theory at present. The big bang can be thought of as a quantum event, originating from very chaotic space-time in which the other quantum fluctuations might have led to other parallel universes. 27

28. Cosmic Inflation The standard big bang has trouble explaining why the universe is as smooth and flat as it is, leading to the idea of an epoch of extremely rapid inflation, just 10 -35 sec after the big bang. The mechanism is unclear but probably associated with the Grand Unified theories that seek to unite all the forces except gravity. 28

29. Status of Inflation Inflation makes the universe flat and smooth (by design!), and it implies vast region of space that are beyond view. It has tentative support from CMB satellite data. 29

30. Beyond the Horizon The universe is bounded in time and not space. General relativity sets no speed limit to the expansion. As time goes by, ever more distant regions come into view. At z = 1.3, an object was moving away from us at c at the time the light was emitted. At z = 1000, two distant points were moving apart at ~60c at the time the radiation was emitted. Consequence of standard big bang: The physical universe is much larger than the observable universe, we are subject to a horizon. Consequence of the inflationary big bang: A microscopic region of space-time became our universe; the universe is a quantum entity. 30

31. Us Milky Way Earth THE UNIVERSE AND US Solar System UniverseMultiverse?

32. Multiverse 32

33. Science is Seeing Life occurs in a range of scales that extends from galaxies to the atomic nucleus, as symbolized by the ancient symbol of the ouroboros, the snake that eats its own tail Beyond the Horizon 33

34. Quantum fluctuations are a mechanism for multiple realizations of the universe …leading to the concept of the “multiverse” 34

35. String Theory Landscape Perhaps 10 different vacua 500 de Sitter expansion in these vacua create quantum fluctuations and provide the initial conditions for inflation. String theory provides context for the “multiverse” 35

36. The “ekpyrotic” universe has a big bang, but it is not ever at an infinite temperature and density, and it is not the origin of all space-time… So our universe emerged from a collision of two 4D branes that are embedded in 5D space-time. The collision is the engine for expansion and matter creation. 36

37. Eternal Universe 37

38. Dark matter binds galaxies and dark energy is currently driving the cosmic acceleration. 38

39. Nature of the Expansion The early expansion was rapid, driven by intense radiation. It slowed down as the dark matter began to dominate, and more recently has begun to accelerate due to the relative growth of dark energy. 39

40. Within the expanding and cooling universe gravity formed stars, galaxies, and people. 40