1. Dr. Bill Pezzaglia Cosmology Interview West Valley College Aug 6, 2013

2. 2
2013 Aug 06
Cosmology
Dr. Bill Pezzaglia

3. Andromeda The Chained Maiden Pegasus The Flying Horse Alpheratz Markab
M31 Andromeda Galaxy
Alpheratz
Markab
Pegasus
The Flying Horse

4. Cosmology The UNIVERSE: Eternal, infinite, unchanging? Or4
The UNIVERSE:
Eternal, infinite, unchanging? Or
Had a beginning, and may end?

5. Outline The Infinite Universe The Finite Universe5
The Infinite Universe
The Finite Universe
The Expanding Universe
Big Bang vs Steady State
Summary

6. I. The Infinite Universe6
A. Copernican Cosmological Principle:
We do not occupy a special location in space (no preferred center)
Universe is isotropic & Homogeneous

7. B Newtonian Cosmology 7
Newton proposed that the universe must be infinitely filled with stars to be balanced
a finite universe would collapse due to gravity
But:
1823 Olber shows universe is not infinite
1920 Eddington shows Newton’s Universe is still Unstable and would collapse

8. C.1 Olber’s Paradox (1823?) Heinrich Olber 1758-1840
discoverer of the minor planets Pallas and Vesta
If the universe is infinite in extent, and filled with stars, Why is the sky dark at night?
For example, in this cactus forest, if you look between two cacti, you just see another cactus further away. In some places you see blue sky because the forest is not infinite, but if it was, you’d just see cacti everywhere, and so the universe would be “green”.

9. C.2 Olber’s Paradox 9
It’s the same with stars. If you look between two stars, you will just see another. Everywhere the sky should be as bright as the sun!

10. II. The Finite Universe size (no galaxies far away)10
Solutions to Olber’s Paradox might be that the Universe might be finite in:
size (no galaxies far away) or
time (no galaxies in distant past)

11. A. Finite Size Universe 1917 Einstein proposes static universe:11
1917 Einstein proposes static universe:
Is finite, curved like a ball
But gravity would still collapse it
Proposes negative pressure (cosmological constant) prevents collapse (now called “dark energy”)
Later calls this his “biggest blunder”

12. B. Curved Space 12
If we live in a (positively) curved space, then no matter what direction we look, we might see that back of our head!
Its like living on the surface of a big ball.
This would explain why sky is dark at night.

13. C. Finite Age of Universe13
Lookback Time:
The further away we look, the further into the past we are seeing
Look far enough away the sky will be “dark” because stars (galaxies) have not yet formed!

14. III. The Expanding Universe14
Evidence suggests the universe is NOT static.
It is expanding with time

15. A. Galactic Recession 15
Recall from earlier lectures that stars (galaxies) show absorption spectral lines
1912 Vesto Melvin Slipher observes redshifts (lines shifted towards red) of galaxies
1917 Willem de Sitter interprets as a Doppler effect, meaning that the galaxies are moving away from us (known for a time as the “de-Sitter effect).

16. B. Big Bang Theory 16
1922 Friedmann, and 1927 Father Lemaitre show that another solution to Einstein’s equation would be that the universe is expanding from kinetic energy leftover from a “big bang” creation. No need for negative pressure.
This would also explain the observed “redshifts”

17. C.1 Hubble’s Law 17
To visualize the expansion of our three-dimensional universe, imagine a two-dimensional universe crisscrossed by a grid of parallel lines (like on a piece of graph paper). The animation shows five galaxies that happen to lie where gridlines cross. As the universe expands in all directions, the gridlines and the attached galaxies spread apart. From the viewpoint of any one of the galaxies, all the other galaxies appear to be moving away. The more distant a galaxy is, the more rapidly it appears to be receding.
1929 Hubble’s Law

18. C.2 Hubble’s Law (1929) 18
(recessional speed) =(const)x(Distance)
Or: v = H d
H=Hubble’s Constant, which will be the “slope” of the line. The approximate value is 75 km/(sec-MPC)
MPC=megaparsec (a million parsecs).
If the universe has been expanding at a constant rate, then by “playing the movie backwards”, 13 billion years ago the universe was a single point (big bang!)

19. IV. Big Bang vs Steady State19
An expanding universe does not necessarily mean that there was a “big bang”
The Universe can be homogenous in time, always getting bigger, without a beginning.

20. A. Steady State Model 20
1948 Sir Fred Hoyle (and others) propose that the universe may appear to be expanding, but its actually not changing. Matter is constantly created to keep the “flow” going.
“Every cluster of galaxies, every star, every atom had a beginning, but the universe itself did not."
He ridiculed LeMaitre’s theory by calling it the “big bang” theory.

21. B. Cosmic Background Radiation6
1960 Penzias & Wilson measure it (Nobel Prize 1978). It was predicted in 1948 by Alpher, Bethe and Gamow in a famous paper, that there would be leftover radiation after the big bang explosion, corresponding to a black body curve at 3000 degrees. Today its at 3 degrees, telling us the universe has expanded 1000x since that time.

22. C. Evidence: Hubble Ultra Deep Field22
March the Hubble Telescope probed a small area about three minutes of arc square, showing 10,000 galaxies.
The most distant galaxies, nearly 13 billion years old, appear to be small irregular “protogalaxies”, i.e. the first building blocks which merged to form the modern day normal-sized galaxies

23. V. Summary The “Copernican Cosmological Principle” is that23
The “Copernican Cosmological Principle” is that
(a) The sun is the center of the universe
(b) There is no center to the universe
(c) The universe is a ball of curved space
(d) The earth is the center of the universe
(e) none of these

24. Question 2 The evidence favors that the Universe:24
The evidence favors that the Universe:
(a) is homogeneous in time
(b) is constantly creating matter
(c) had a “big bang” beginning
(d) is infinite in size
(e) none of these

25. Question 3 25
What is the best argument against the Steady State model of the universe?
(a) Detection of primordial radiation
(b) Detection of Galactic redshifts
(c) Hubble’s law
(d) Olber’s Paradox
(e) none of these