Cosmology and the Evolution of the Universe

Edwin Hubble, 1929: -almost all galaxies have a redshift

-moving away from us -greater distance greater redshift

Implications of the Hubble Law:

- Universe is changing (getting bigger!) - it is not static, unchanging

- Universe had a beginning !! - could not have been expanding forever

HUBBLE LAW: v = Ho r v = velocity (speed); r = distance

Rate of expansion: Ho= Hubble constant (slope of line)

The Hubble Constant tells us: - Size of observable universe

largest redshift = largest distance

- Age of universe how long ago everything was together

- Fate of universe what will happen in future

Most accurate measurements (2014):

Ho = 70.4 to 74.3 km/s per Mpc

Age = 13.25 to 13.98 billion years

The Big Bang Model

Universe began from a single point - that was extremely dense and hot

Cosmic Singularity

- "Explosion" of matter and energy (and space and time!)

-today, still expanding

- properties of universe change with time - had different conditions in the past - will have diff. conditions in future

- ultimate fate is unknown The Early Universe:

Initially was very HOT! - Hot enough for Hydrogen fusion

everywhere in space! - explains why 25% of universe is

Helium Basic Principles of Big Bang Model

1. Universe cools as it expands: Time

Temperature

0.01 s

100 billion Kelvin

180 s

1 billion Kelvin

400,000 yrs

3000 Kelvin

2. High energy radiation (photons) create matter

E = m c2

electron

Gamma Rays

positron

3. Energy of radiation (photons) depends on temperature of universe

- As universe expands and cools - radiation loses energy - universe is a blackbody

PREDICTION: According to Big Bang Model:

What is temperature of universe TODAY? Prediction: 3 Kelvin (1964, Peebles and Dicke, Princeton Univ.)

1964, A. Penzias and R. Wilson (Bell Labs)

-built antenna for satellite communications

-detected "noise" in all directions -background noise corresponds to temperature of 3 Kelvin!

Energy leftover from the

BIG BANG !!!

“Cosmic Microwave Background” (CMB)

1989, satellite COBE - accurate measurements of Cosmic Microwave Background

- Temperature of Universe: T = 2.725 +/- 0.002 K

Expansion of the Universe: - the space between objects is expanding - objects are not moving through space.

Cosmological Principle: - there is no center, no edge - every location appears to be at

center

- same at every location (large scales) “Homogeneous”

- same appearance in every direction “Isotropic”

Clusters, Superclusters, Voids - origins should be seen in the CMB - 1992, temp fluctuations of 0.0002 K - seeds of large scale structure

Surprising Discovery in 1998:

- rate of expansion is increasing!

- previously thought that gravity would slow expansion over time

- what can overcome affects of gravity? - repulsive, anti-gravity force

- “Dark Energy”

Fate of the Universe: Three Possible Fates:

- based on overall density of universe - need to know total mass - need to know overall size (Ho)

Closed Universe: - expansion will eventually stop - gravity will cause universe to collapse

- Universe will end in "Big Crunch" - maybe start again (?)

Overall geometric “shape” of universe is spherical

Flat universe: - expands forever, always slowing down - not enough gravity to start collapse - Universe will end in “Cold Death” - all forms of energy becomes evenly distributed in space. - everywhere in universe is same temperature -close to absolute zero

Overall “shape” of universe is flat.

- Flat universe is predicted by current theories.

Open Universe:

- expands forever, possibly going faster and faster

- dark energy overwhelms gravity

- Universe will end in “Big Rip” - dark energy overwhelms all other forces. - expansion will accelerate so much, all matter will get ripped apart Overall “shape” of universe is hyperbolic.

TIME EVENT 0 – 10-43 seconds

The Planck Time: Nothing is known during this time. ?

10-35 – 10-32 seconds

Inflation: Universe goes through period of enormous expansion, grows by factor of 1043!!

Radiation Dominated

Universe (Primordial

Fireball)

10-8 – 10 seconds

Production of Matter: quarks and electrons created from extremely hot photons

10 – 300 seconds

Nucleosynthesis Era: 2H and 4He created by fusion reactions throughout the universe

400,000 yrs Era of Recombination: Electrons combine with nuclei to form atoms; (T = 3000 K), space is now transparent

Matter Dominated

Universe (Transparent)

1 – 2 billion years

Formation of Galaxies: Young galaxies seen as quasars

9 – 10 billion years

Formation of Solar System: Sun and planets form within the Galaxy (4.6 billion years ago)

Today (14 billion years)

Universe still expanding; Average temperature T = 2.725 K