Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

The Big Bang

The universe is expanding now, and was denser & hotter in the past

The three pillars of the big bang

Cosmological expansion (1930s)

The Cosmic Microwave Background Radiation (60s)

The abundances of light elements (40s−70s)

The important numbers

The open questions

Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

The History of Cosmology

Cosmology − study of the history and evolution of the Universe

(kosmos, order, universe + logia, speech, word, reason)

16th C. − Copernicus/Galileo − the sun vs. the earth at the center?

17th − 20th C. − Newton, Kant, Laplace, Herschel

What are the nebulae? “Island Universes”/Galaxies

1920s: The Shapley/Curtis debate

20th C. − Einstein, Hubble − Steady State vs. Big Bang

Theory: General Relativity(Freedman, Robertson, Walker, LeMaitre)

Observation: Expansion

Finally resolved in favor of the Big Bang only in 1950s−1970s

Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

The Three Pillars of the Big Bang

Cosmological expansion

All galaxies are moving away from one another

No center, no edge!

The Cosmic Microwave Background Radiation

Light (photons) from the hot (3000K!) early universe, cooler now (3K)

Picture of the universe at early times

The abundances of light elements

Hot enough for fusion!

4 Hydrogen → 1 Helium and beyond

(Lithium, Deuterium...)

Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

The Parameters of the Big Bang Theory

H0, Hubble’s constant:

How fast is the universe expanding?

Ω: What are the components of the universe?What is the geometry of the universe?

Normal matter: ~5%

Dark Matter: ~25% what is it????

“Dark Energy”/“Vacuum Energy”: ~70%

Accelerating universe???

t0: What is the age of the Universe?

(actually, determined by the answers above!)

Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

Open Big Bang Questions

What are those parameters in detail?

Why is the universe flat?

Why are there galaxies? What formed the initial perturbations that grew into the ones we see today? How did they grow?

What is the dark matter?

Why is there more matter than antimatter?

Why is there anything at all?

Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

Cosmic Microwave Background

Boomerang + Maxima: The universe is spatially flat!

Physics 24 B. Sadoulet/A.H. Jaffe 31 August 2000

From Quarks to the CosmosBig Bang enables influence of infinitely small on infinitely large