Ch 17--Fate of the Universe

1. Ch 17--Fate of the Universe ASTR103, GMU, Dr. Correll

2. What do you think? • What is the universe? • Did the universe have a beginning? • Will the universe last forever? ASTR103, GMU, Dr. Correll

3. Cosmology • Cosmology--the study of the origin, structure, and evolution of the universe • Scientific underpinnings began in 1915 with Einstein’s General Theory of Relativity • The universe is spacetime • GR allows for a dynamic, evolving spacetime, hence a dynamic, evolving universe is possible • Prevailing view was that the universe is static and unchanging--steady state universe • Hubble’s survey of galaxies revealed the universe to be expanding--the big bang! ASTR103, GMU, Dr. Correll

4. The Big Bang • The Hubble constant gives us an estimate of the age of the universe • imagine running the expansion of the universe backwards--assuming a constant recession velocity, how long does it take to reach the “big crunch?” Time = separation distance = 1/H0 recession velocity = 1 / 75 km/s/Mpc = 13 billion years • General relativity corrects this to be closer to 9 billion years ASTR103, GMU, Dr. Correll

5. Big Bang--a Simple Model • The expanding universe that resulted from the big bang is most accurately thought of in simple terms as a baking loaf of raison bread • the bread dough expands (spacetime) • the raisons do not, they stay the same size but move further apart from each other (matter and galaxies) ASTR103, GMU, Dr. Correll

6. Big Bang--a Better, Simple Model • The expanding universe that resulted from the big bang is most accurately thought of in simple terms as the surface of an expanding balloon • the surface of the balloon expands (spacetime) • galaxies on the surface of the balloon are still best thought of as raisons attached (matter and galaxies) • the surface of the balloon has no edges! ASTR103, GMU, Dr. Correll

7. History of the Universe • In the big bang theory, the earliest moments of after its creation, the universe was a ultra-dense, ultra-hot, yet infinitesimally small place • Important events in the history of the universe Time Temp Phenomena 10-43 s 1032 K Quantum gravity 10-2 s 1013 K Particle/photon interchange, formation of light elements 106 yrs 1000 K Atoms form, radiation/matter decouple 1010 yrs 3 K Now--galaxies, stars, life >1032 yrs All matter erodes away?! ASTR103, GMU, Dr. Correll

8. Unified Forces ASTR103, GMU, Dr. Correll

9. Early Matter and Antimatter • During the first second of the universe, matter, antimatter, and radiation were in equilibrium ASTR103, GMU, Dr. Correll

10. Early Matter and Antimatter • After the first second, as the universe cooled, radiation no longer spontaneously creates matter antimatter pairs--matter and antimatter annihilate each other • but, there seems to have been an excess of matter vice antimatter! • Results from a strange property of, once again, quantum mechanics--”right-handedness is not strictly preserved” ASTR103, GMU, Dr. Correll

11. Nucleosynthesis • As the universe continued to cool, hydrogen could undergo nuclear reactions forming helium and lithium--nucleosynthesis • After the first three minutes, hydrogen, helium, and lithium rations were established ASTR103, GMU, Dr. Correll

12. Radiation/Matter Decouple • For the first 300,000 years, radiation too intense to allow electrons to be captured by nuclei • at about 300,000 years, temperature became cool enough for electron and protons to combine forming hydrogen atoms • the radiation field decoupled from matter and evolved separately ASTR103, GMU, Dr. Correll

13. Cosmic Microwave Background • The radiation field cools as the universe expands leaving a fossil remnant of the big bang • predicted by Alpher, Gamow and Bette in 1948 • discovered by Penzias and Wilson in 1965 • Measured by COBE satellite in 1990- ASTR103, GMU, Dr. Correll

14. How Big is the Universe? • We can see back in time to the edge of the observable universe • Distant regions in the universe look the same, this isotropy and homogeneity indicate the universe was once all in causal contact, even though it now isn’t • The inflationary universe solves this conundrum ASTR103, GMU, Dr. Correll

15. Acausal Isotropy ASTR103, GMU, Dr. Correll

16. Inflationary Universe ASTR103, GMU, Dr. Correll

17. Formation of Galaxies • Galaxy formation began in the first billion years of the universe • Elliptical galaxies form stars at a faster rate, possibly preventing the collapse of the proto-galactic cloud into a disk • Slower star formation rate allows disk to form leading to spiral galaxies ASTR103, GMU, Dr. Correll

18. Fate of the Universe • Will the expansion continue forever (the “big chill”), or will the universe eventually contract into a “big crunch” • GR allows for three scenarios • Unbound (expands without limit • Bound (will eventually collapse) • marginally bound (expands forever, but with a limit) ASTR103, GMU, Dr. Correll

19. Is the Universe Flat or Curved • Bound • spherical geometry • Marginally bound • flat • Open • Hyperbolic ASTR103, GMU, Dr. Correll

20. Observational Data • Data not yet conclusive, but universe is very nearly flat! • Recent data from supernovae observations indicate expansion may be speeding up! Verdict still out. ASTR103, GMU, Dr. Correll

21. What do you think? • What is the universe? • It’s all matter, energy, and spacetime • Did the universe have a beginning? • Yes, probably occurred between 12-18 billion years ago in an event called the “big bang” • Will the universe last forever? • Current observations support the belief that it will last forever ASTR103, GMU, Dr. Correll

22. Questions for Thought • Describe the history of the universe, explaining why the big bang theory is the prevailing accepted theory, and describing observational evidence which supports this theory. (probably a mandatory question) ASTR103, GMU, Dr. Correll