1. THE EXPANDING UNIVERSE

2. How objects are moving
Objects moving away from us appear redder than actually are due to the appearance of lengthening waves.
Objects approaching have their light waves shifted toward blue (shorter wavelengths)
This occurs with both light (shift in color) and sound (Shift in pitch) and is known as the Doppler Effect

3. The Expanding Universe
 Red Shifts
• (Red end of spectrum) - light waves “stretched,” shows that Earth & source are moving away from each other.
 Hubble’s Law: states that galaxies are retreating from us at a speed that is proportional to their distance
• Red Shifts of distant galaxies indicate universe is expanding.
Also, no matter where a galaxy is located in the universe, every other galaxy (except those in the SAME cluster) will be moving away.

4. Did the Universe Begin?
Any theory about the origin of the universe MUST account for the fact that all distant galaxies are moving away from us.
If the universe is expanding, every galaxy would be moving away from every other galaxy.
BIG BANG THEORY: the universe began as a violent explosion from which the universe continues to expand, evolve, and cool.

5. George Gamow Big Bang theorist in 1948 The Big Bang
 Entire universe was confined to a dense, hot, supermassive ball. About 13.7 bya, violent explosion hurled material in all directions (all matter and space were created at that instant).
 Supporting Evidence F I G 23
• The Red Shift.
• Energy called cosmic back- ground radiation, believed was produced during Big Bang (detected as faint radio signals coming from every direction in space).
George Gamow
Big Bang theorist in 1948

6.  The Big Crunch? (reverse of BIG BANG)
• Future of the universe:
1. Expand forever… (stars will burn out, replaced by invisible matter and black holes that will travel outward through an endless, dark, cold universe).
2. Expansion will stop & gravitational contraction will follow (galaxies will collapse into high-energy, high-density mass from which the universe began).
** View currently favored by most scientists is an expanding universe with no ending point.
(Note, methods used to determine the ultimate fate of the universe have substantial uncertainties)