1. COSMOLOGY Prospects in Theoretical Physics Institute for Advance Study
I am both honored and pleased to be ask to participate in this series. Honored to be part of this impressive cohort of lecturers. And pleased because a School in Superstring Theory is giving attention to Cosmology. I happen to believe that the future of superstring theory is comology and that the future of cosmology is superstring theory. In particular, I think the stage is set for superstring theory to lead to a genuine revolution in cosmology by addressing the problem of the initial singularity. In fact, the revolution may have already begun, as I will explain in these lectures.
The plan of these three lectures is as follows. I am assuming that most of you know little or nothing about cosmology. I want to explain the most important aspects -- the things that everyone interested in string theory should know about. First, I will focus on what we know today about the present universe. Then, I will discuss inflationary cosmology, one of the most important ideas in contemporary cosmology. Then, I will turn to very ideas, an alternative model inspired by string theory and ultimately dependent on progress in string theory to complete the story.
Prospects in Theoretical Physics
Institute for Advance Study
July, 2002

2. What every string theorist should know about the Universe
Inflationary Cosmology
Cyclic Universe
These will break roughly into three lectures,

3. Salient Features of the Universe
• Homogeneity and isotropy
• Universe expanding uniformly
• thermal background of radiation with T~3K
• chemical composition is roughly 75% H, 25% He, + trace
• ordinary matter is more abundant than ordinary antimatter
• nearly scale invariant, adiabatic CMB fluctuations
• universe is spatially flat
• hierarchy of lumpy structure from 1 kpc to 100 Mpc scales
• ordinary matter is a minority (1/6x) of all matter
• matter is a minority (1/4x) of all energy
• expansion rate is accelerating

4. In 1980’s, this was the largest scale map of the universe available, the CfA map of Geller and Huchra.
We lie at vertex looking out at galaxies (dots). We see humunculus, Great Wall, voids. NOT homogenous and isotropic. The scale is 200 Mpc. 1 Mpc = XXX. and is equal to the mean distance between galaxies. So, this map says: go out 200 galactic distances and the universe still seems rather inhomogenous.
200 Mpc
1 Mpc =3.3 x1019 km = 3.26x106 l-yr

5. 1300 Mpc
However, today, we can do better. Here is the 2dF survey -- here looking at 2 cones, Each is about 6x longer. And look. we can see the finer structure that was in the Cfa survey, but no larger structures. The streaky feaures you are seeing are all to do with selection effects of the survey. So, the homogeneit and isotropic set in after 100 Mpc or so --those are the largest structures.

6. Comfirmation is seen in the cosmic microwave background
Comfirmation is seen in the cosmic microwave background. Here we are looking at radiation distribution and yet larger scales. Here the variations are 1 part in Extremely homogeneous. (We will come back and look at the inhomogeneities in a bit.) For the moment, be impressed by homogeneity. Smoother than your desk Mpc. Further we can see. BUT only 60 x inhomogenous scale. Should Einstein be embarrassed?
Why is homogeneity so important? Means we can understand universe from our one vantage point
6000 Mpc

7. Salient Features of the Universe
• Homogeneity and isotropy for Mpc > x > 100 Mpc
• Universe expanding uniformly
• thermal background of radiation with T~3K
• chemical composition is roughly 75% H, 25% He, + trace
• ordinary matter is more abundant than ordinary antimatter
• nearly scale invariant, adiabatic CMB fluctuations
• universe is spatially flat
• hierarchy of lumpy structure from 1 kpc to 100 Mpc scales
• ordinary matter is a minority (1/6x) of all matter
• matter is a minority (1/4x) of all energy
• expansion rate is accelerating

8. H = 72 ±3 (stat) ±7 (sys) km/s/Mpc
Hubble Key Project

9. Consequences • Universe has a finite age • Universe has a horizon
age ~ 1/H ~ 14 Gyrs
• Universe has a horizon
Finite age + finite speed of light
• Can look back in time
red shift (z)  time

10. Salient Features of the Universe
• Homogeneity and isotropy for Mpc > x > 100 Mpc
• Universe expanding uniformly
• thermal background of radiation with T~3K
• chemical composition is roughly 75% H, 25% He, + trace
• ordinary matter is more abundant than ordinary antimatter
• nearly scale invariant, adiabatic CMB fluctuations
• universe is spatially flat
• hierarchy of lumpy structure from 1 kpc to 100 Mpc scales
• ordinary matter is a minority (1/6x) of all matter
• matter is a minority (1/4x) of all energy
• expansion rate is accelerating

11. evidence Universe
was once hotter
than .1 eV

12. evidence
that the
Universe
was once
hotter
than
1 MeV
evidence of
baryon
asymmetry

13. Salient Features of the Universe
• Homogeneity and isotropy for Mpc > x > 100 Mpc
• Universe expanding uniformly
• thermal background of radiation with T~3K
• chemical composition is roughly 75% H, 25% He, + trace
• ordinary matter is more abundant than ordinary antimatter
• nearly scale invariant, adiabatic CMB fluctuations
• universe is spatially flat
• hierarchy of lumpy structure from 1 kpc to 100 Mpc scales
• ordinary matter is a minority (1/6x) of all matter
• matter is a minority (1/4x) of all energy
• expansion rate is accelerating

14. compare temperature at two points angle q apart
write down T autocorrelation function. explain delta T/T ~ delta Phi
compare temperature at two points angle q apart

15. ~ p/l

16. outside the horizon at last scattering
temperature fluctuation
Large angular scales
outside the horizon at last scattering
Focus in on small l or largest scales
temperature fluctuation

17. temperature fluctuation
What is striking about these fluctuations is that they are beyond he horizon
temperature fluctuation

18. ~ p/l