Cosmology

1
Cosmology

• Origin, early history, and fate of the Universe
• Does the Universe have a beginning? An end? What
  physics processes caused the Universe to be
  what it is? Are other universes possible? Would
  they look like ours (have the same physics)?
• Indication that the Universe is expanding, and it
  has been ever since it was created in the Big
  Bang about 13 billion years ago
• Cosmological Principle - the Universe appears the
  same from any location
• - no center
• -no edge

2
Expanding Universe

• Measurement of Hubble constant gives age about
  15 billion years - depends on how Hubble
  constant is changing with time
• As the Universe expands it cools down. At its
  earlier times it was much, much hotter.
• If the Universe keeps on expanding forever
  everything will come to a cold end, the stars
  will all end there lives and no new ones will be
  formed (Open Universe)
• if the expansion stops and a contraction begins
  the Universe will heat up as it returns to a hot
  state similar to when it was formed (Closed
  Universe)
• Not unambiguously known what fate will be

3
Expanding Universe II

• Hubble constant H changes with time
• Gravity can slow the expansion rate (by pulling
  inward)
• How rapidly H changes depends on the amount of
  matter - we seem to be very close to the Critical
  Density which separates an Open from a Closed
  Universe (hint of underlying physics?)
• recent (perplexing) data indicated Universe is
  accelerating! Like anti-gravity!

4
Fire and IceRobert Frost - 1923

• Some say the world will end in fire,
• Some say in ice.
• From what Ive tasted of desire
• I hold with those who favor fire.
• But if I had to perish twice,
• I think I know enough of hate
• To say that for destruction ice
• Is also great
• And would suffice.

5
Hubble Law - Age of Universe

• Hubble Law -- v Hd
• Universe is expanding. Work backwards to estimate
  when time began
• assume constant velocity (not true)
• time distance/velocity d/v
• d/Hd 1/H
• so 1/H is about the age of the Universe
  

Time now Distance d
Time 0
Velocity v
6
Beginning of Universe

• Sometime called Big Bang but not normal
  explosion moving outward into existing 3D space
• explosion occurred everywhere at same time and
  expanding universe create its own space as it
  expands outward
• Einstein predicted in 1915 general Theory of
  relativity

7
Expanding Universe
Time 1
Red void nothingness (hard to picture). Space
just gets bigger with time
Time 2
Time 3
8
Expanding Universe

• No edge, no center to Universe
• Consider balloon. 2D surface in 3D space. All
  points moving away from each other with v Ad.
  All points are the same no edge or center
• Universe is 3D surface on a D manifold
  (wormholes burrow through this)

9
Expanding Universe III

• As Universe expands it cools
• Physical processes at any time depend on
• -Temperature
• -Nature of forces and particles
• Current Temperature is 3 degrees K
• We can see light back to a time when the
  universe was still transparent when temperature
  is below 3000 degrees. Before then Universe was
  opaque

10
Expanding Universe IV

• When temperature above 3000 degrees Universe is
  opaque as atoms are ionized - free H, He nucleii
  plus free electrons
• Formation of atoms allows for transparent
  Universe -- occurred about 1,000,000 years after
  beginning
• Burst of light everywhere - now observed as 3
  degree microwave background -- (1964 Bell Labs)

11
Microwave Background

• When emitted at time 1,000,000 years
• Temp 3000 degrees
• wavelength 1 micron (visible)
• Same photons observed now. Universe has
  expanded/stretched by 1000 (all directions)
• Temp 3 degrees
• wavelength 1 mm (microwave)