The Last Epoch

1. The Last Epoch Sections 39.1-39.3

2. Reminders • Final Mallard-based reading quiz due prior to start of next class (Ch 39.4-39.5). • There are no more labs or weekly reflections. • Final exam December 13, Thursday, 7:50 AM - 9:50 AM dealing with Chs. 29, 37–39 (23 points) andreview(12 points) plus extra creditbased on questionsfromearlierchapters (5 points).

3. Cosmic Structure Formation • A matter dominated universe ruled by the force of gravity. • Slight variations in density produces formation regions for stars and galaxies. • New stars and galaxies have 74% H & 26% He by mass (just like the universe as as a whole)

4. Star Formation • As H and He accrete, gas pressure increases limiting further growth unless there is sufficient matter. • The Jeans mass (≈ 105Msun) constitutes the minimum amount of mass required for star formation (corresponds to globular star cluster). • Collapses of smaller clouds are helped along by: • stochastic processes (wakes of exploding stars or two or more gas clouds merging) • compression by magnetic field of galaxy

5. Wrinkles in Spacetime • COBE observed the Cosmic Microwave Background, but there was an ever so slight variation in temperature (and thus density) from point to point across the sky.

6. Problems with the Standard Model of Cosmology • The standard model works quite well, explaining: • Olber’sparadox • X, Y, and Z abundances (74%, 26%, and 0%) • Hubble’s relationship, v = Hd • 2.7K cosmic background radiation • Three major problems remain with model: • The Flatness Problem • The Horizon Problem • The Structure Problem

7. The Flatness Problem • If shortly after the Big Bang, the universe was even remotely non-flat, we would not have the relatively flat universe we observe today. • Why did the universe’s original flatness balance on a knife’s edge when so many other possibilities existed?

8. The Horizon Problem • The cosmic microwave background is amazingly uniform but for very minute variations equal to about 0.00001 K. • How is this possible when opposite “ends” of the universe cannot “communicate”?

9. The Structure Problem • Friedmann’s assumption of homogeneity and isotropy is not entirely correct as seen in the pockets of higher density in the universe such as shown in the cosmic background radiation. • How is it possible that galaxies too far apart to “communicate” can still look pretty much the same as a function of distance throughout the universe? This problem is amplified by the fact that we don’t really understand galaxy formation.

10. Inflationary Cosmology • In an attempt to solve these three problems, the suggestion was made of an inflationary period in the early universe. • Between 10-34 and 10-32 seconds after the Big Bang, the universe grew exponentially – from the size of a nucleon to approximately 85 LY. • Inflation is a part of modified field equations and solves 3 problems mentioned earlier.

12. Review: Section 8.1 • Work-energy relationship, Fd = ΔE (not be confused with impulse-momentum relationship, FΔt = mΔv) • Conservation of energy, Ei = Ef • Energy and power definitions: • KE = ½mv2 • PEg= mgh • PEe = ½kx2 • P = E/t

13. Review: Chapter 11 • Definitions of wave forms: transverse and longitudinal • Definitions: • Amplitude, wavelength, frequency, speed, period • T = 1/f and λf = v • Note well that v = c if we are dealing with electromagnetic radiation • Polarization, interference, diffraction • The Doppler effect, Δλ/λ = v/c (non-relativistic)