Astronomy 100 -- Cosmology

THE UNIVERSE:
THE END AND THE BEGINNING

The discovery by Hubble that the Universe is expanding uniformly is one the MAJOR DISCOVERIES in Astronomy. The Hubble Constant is the RATE OF EXPANSION OF THE UNIVERSE!

TWO MAIN IMPLICATIONS:
• The Universe is CHANGING!
  Opposes the "Steady-State" Universe, that the Universe has always been and always will be the same.
• The Universe had a BEGINNING!
  Winding the clock backwards would bring all the galaxies together.

TWO QUESTIONS ABOUT AN EXPANDING UNIVERSE:

1) What will happen to it?
COSMOLOGY
2) How did it start?
COSMOGONY

---

---

COSMOLOGY

A Couple of Definitions:

TO BOUND (verb transitive): To provide a limit to.

INFINITE (adjective): Having no boundaries or limits.

Immeasurably great, as in duration or extent.

These two definitions are not necessarily contradictory!! Here are some examples of adding infinite amounts together that add to a certain amount:

 1   1   1    1    1    
 - + - + - + -- + -- + ... = 1
 2   4   8   16   32


 1   1   1   1   1         (pi)2
 - + - + - + - + - + ... = -----
 12  22  32   42  52          6


 1   1   1   1   1         (pi)2
 - + - + - + - + - + ... = -----
 16  36  56   76  96         960

---

THE EXPANDING UNIVERSE

• We are NOT at the center! (No one is!!)
  All observers see the same thing!
  (center of Time, not Space)

• The Universe has a finite age!
  Best scientific determination is 13.8 billion years!

• There was a beginning to the Universe!
  This is called the "Big Bang", but a better name would be the "Big Expansion".

---

FATES OF AN EXPANDING UNIVERSE

After Hubble's discovery of the expansion of the Universe, great effort was made to determine the future of the Universe. Simply considering only gravity, there were 3 possibilities:

1) OPEN UNIVERSE
The Universe will expand forever. Eventually, everything will burn out.

2) FLAT UNIVERSE
This is the borderline case between the Open and Closed Universes. The Universe will continue to expand, but slows down and never stops. Just enough energy to keep going.

3) CLOSED UNIVERSE
This Universe will have enough gravitational pull to bring itself back together in what is sometimes called "The Big Crunch".

---

---

WHAT DO WE KNOW ABOUT THE
FATE OF THE UNIVERSE

Recent observations suggest that gravity is not the only property that is determining what will happen to the Universe. Based on distances to SUPERNOVAE, two teams of astronomers have shown that the Universe is actually accelerating, rather then decelerating, in its rate of expansion. The cause of this acceleraltion is referred to as "Dark Energy"!

While this makes the Universe much more complex for astronomers to try to understand, the Universe will continually expand meaning we have an

OPEN UNIVERSE!
- - - - - - - - - - - - - - -