Cosmology

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

2. 2 2013Aug 06 Cosmology Dr. Bill Pezzaglia

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

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

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

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

7. 7 B Newtonian Cosmology • 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 Universeis still Unstable and would collapse

8. 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 youlook between two cacti, you just seeanother cactus further away. In someplaces you see blue sky because theforest is not infinite, but if it was, you’djust see cacti everywhere, and so theuniverse would be “green”.

9. 9 C.2 Olber’s Paradox 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 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) 10

11. 11 A. Finite Size Universe • 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. 12 B. Curved Space 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. 13 C. Finite Age of Universe • 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 Universe Evidence suggests the universe is NOT static. It is expanding with time 14

15. 15 A. Galactic Recession • 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. 16 B. Big Bang Theory • 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. 17 C.1 Hubble’s Law 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. 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!) 18 C.2 Hubble’s Law (1929) (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).

19. IV. Big Bang vs Steady State 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. 19

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. 6 B. Cosmic Background Radiation 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 Field 22 • March 2004 -- 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. 23 V. Summary 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. 24 Question 2 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. 25 Question 3 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