1. Cosmology

2. Some important questions Did the universe have a beginning or has it always existed? Will the universe end? If it ends, what will happen at the end? Is the Universe infinite or does it have a boundary?

3. The Universe is expanding! During the 1920s, Edwin Hubble and Milton Humason found that galaxy spectral lines were redshifted The distant galaxies are moving away from us! The Universe is expanding!

4. Hubble’s Law The most distant galaxies had the largest redshifts and speeds.

5. Hubble’s Law velocity of galaxy = H o d =(Hubble’s constant) (distance to the galaxy)

6. Expansion without a Center

7. The Universe is not infinitely old! If the universe is expanding, it must have been smaller in the past In the beginning of time all material was in a “singularity” with infinite density The Universe is 14 billion years old

9. An “event” called the BIG BANG created the Universe and caused it to expand

10. COsmic Background Explorer (COBE) Satellite (1990) Penzias and Wilson (1965) The 2.7K cosmic microwave background radiation that fills all space is evidence for the BIG BANG

11. Cosmic Microwave Background Radiation By COBE 1990

12. Cosmic Microwave Background Radiation By WMAP 2001

13. Structure of the Universe

14. Figure 17.18 The Inflationary Universe

15. Cosmological Timeline

16. Figure 17.15 E=mc 2 : Energy turn into mass- particle and antiparticle pairs

17. Fire and Ice “Some say the world will end in fire, Some say in ice. From what I’ve tasted of desire I hold with those who favor fire. But if it had to perish twice, I think I know enough of hate To say for destruction ice Is also great And would suffice” - Robert Frost

18. Fire? If we live in a high density closed Universe: The expansion of the Universe will stop. The Universe will collapse; all matter and energy will be squeezed back into a singularity at high temperatures If we live in an oscillating Universe: Cycle of Collapse then rebirth in another “Big Bang”

19. Ice? If we live in a low density open or critical density flat Universe, the Universe will expand forever: 1.stelliferous era: lots of stars 2.degenerate era: brown dwarfs, white dwarfs, black dwarfs, neutron stars, black holes, planets 3. black-hole era: only objects left are black holes which will eventually evaporate 4.dark era: low-energy photons, neutrinos, and some elementary particles (10 110 years) The Universe would be a cold, lifeless, lonely world!

20. Geometry and Fate of the Universe Critical Density: Flat and Infinite in Size High Density: Closed and Finite in Size Low Density: Open and Infinite in Size

21. In the past we thought we live in a low density Universe... The Universe is open and will expand forever!! If the force of gravity is acting on the Universe, the expansion should be slowing down

22. But there may be a force that is speeding up the expansion of the Universe! If the Universe is speeding up, there must be a force that acts opposite to gravity This “fifth” force should be a long range repulsive force -“anti-gravity” Suggests that vacuum has a nonzero, positive energy density called dark energy

23. Dark Energy Dominates all of Space! Dark Energy causes space to expand faster with time Energy density due to dark energy + the density to matter exactly = The Critical Density!

24. Now... There is enough density so that it equals the critical value for the Universe to be flat! Only 30% is made of matter and 70% is made of dark energy!

26. Something to think about… Is our Universe the only universe or could it be one of many??? Do they exist in other dimensions??? Can we access them through wormholes???

27. Multiverse Theory New universes can sprout out within any black hole?

28. The Superstring Theory Each fundamental particle (quark, electron, neutrino) is a different vibration mode of a tiny, elongated, one-dimensional energy packet called a “string” “strings” are so small (10 -33 cm), they are almost point-like Universe is 11-dimensional, but 7 of the dimensions are too small to see