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
0 – 10-43
seconds
10-35 – 10-32
seconds
10-8 – 10
seconds
10 – 300
seconds
400,000 yrs
1 – 2 billion
years
9 – 10 billion
years
Today (14
billion years)
EVENT
The Planck Time: Nothing is known during
this time.
Inflation: Universe goes through period of
enormous expansion, grows by factor of
1043!!
Production of Matter: quarks and electrons
created from extremely hot photons
Nucleosynthesis Era: 2H and 4He created by
fusion reactions throughout the universe
Era of Recombination: Electrons combine
with nuclei to form atoms; (T = 3000 K),
space is now transparent
Formation of Galaxies: Young galaxies seen
as quasars
Formation of Solar System: Sun and planets
form within the Galaxy (4.6 billion years ago)
Universe still expanding; Average
temperature
T = 2.725 K
?
Radiation
Dominated
Universe
(Primordial
Fireball)
Matter
Dominated
Universe
(Transparent)