1. Cosmology: The Study of the Universe as a Whole Physics 360 Geol 360 Astronomy John Swez

2. Ancient Cosmology: Why A Finite Age Universe Even simple observations can lead to thoughtful questions about the Universe Olbers’ Paradox – Why is the night dark? Newton’s Law of Gravity – Why hasn’t everything fallen together?

3. Why A Finite Age Universe: Olbers’ Paradox (1823) Assume Universe is infinitely old Then every line of sight will cross a star The Night Sky would not be black The black night sky implies the Universe is finite

4. Why A Finite Age Universe: Newton’s Law of Gravity Every object attracts every other object in the Universe Therefore, every star attracts every other star After infinite time, all stars should clump together into one big blob This could imply a finite aged Universe, or (from Newton) Divine Intervention

5. Modern Cosmology Observations Things Any Modern Cosmology Must Explain Expansion of the Universe Cosmic Microwave Background Radiation Evolution of the Universe Cosmic Element Abundances

6. Interpreting It All: The Underlying Principles of Cosmology Universality –The same laws of physics apply everywhere Isotropy –At large scales, from any point the Universe looks the same in every direction Isotropy with time would also be aesthetically pleasing, but doesn’t hold

7. Expansion of the Universe Edwin Hubble: The redshift of the wavelength of spectral lines increases with distance This is equated with expansion

8. Balloon Model of Expansion Each button on the surface of a balloon expands away from all other buttons The Universe is a 3-dimensional version of this

9. Expansion of the Universe Redshift of galaxies proportional to distance Implication: The Universe is Expanding Implication: In the past, the Universe was more dense than now

10. Redshift Interpretation The redshift is due to space expanding, not a velocity effect Space stretches light as it expands Longer light is redder light

11. What Expansion Is Not Redshift is due to space expanding between galaxies Expansion is not ‘into’ anything The Universe doesn’t need an ‘edge’ The Universe and expansion can be everywhere

12. Cosmic Background Radiation Space is filled with 2.7K blackbody radiation This peaks in the microwaves It has small variations, but is basically very uniform

13. Evolution of the Universe Gas clouds collapse into stars, which die Galaxy shapes vary with distance/time Number of radio galaxies increases with distance/time Older stars have less heavy elements like carbon and oxygen Implication: The Universe is changing

14. Galactic Evolution Hubble Deep Field A view of the most distant galaxies observed Many shapes besides common (spiral, elliptical) types

15. Cosmic Element Abundances The Universe appears to be –~73% Hydrogen –~25% Helium –~2% everything else This appears to be true for most every star, in most every galaxy Deuterium abundance can’t come from stars Isotope ratios for Helium and Lithium are also the same everywhere

16. Modern Cosmology Observations (recap) Expansion of the Universe Cosmic Microwave Background Radiation Evolution of the Universe Cosmic Element Abundances

17. Big Bang Theory In the past, the Universe was very hot and dense The Universe is expanding Therefore, the Universe is cooling  Modern Universe Most credible theory of the early Universe Supports all the modern observations Does not address the origin of the Universe

19. Early Universe E=mc 2  e + + e -

21. Fate of Universe General Theory of Relativity Energy/Mass shapes space and slows the expansion Cosmological Constant (‘dark force’) increases expansion Open: Universe expands forever Flat: Universe barely expands forever Closed: Universe eventually contracts

22. Geometry of the Universe Spherical –Surface of a sphere –Finite size Flat / Euclidean –‘Normal’ geometry –Infinite size Hyperbolic –Surface of a saddle –Infinite size

23. Not Observed! Observed!

24. Dark Force Cosmological Constant ‘Negative Pressure’ or ‘Dark Force’ Strong only over very long distances (between galaxies) A static universe requires it to fight gravity (Einstein invented it for this) An expanding universe does not require it (until recently, it was discounted) It may now dominate Universal expansion

25. Expansion Age of the Universe Running expansion backwards -> start Depends on current and past expansion rates Depends on relative strengths of: –gravity –Dark force, which may vary over time

26. Fate of Universe

27. Latest Results The expansion rate is measured by knowing the distance to very distant objects Type I Supernova are exploding stars (very bright!) and good distance indicators Recent observations support a universe where the expansion is now dominated by the Dark Force

28. Gravity Vs Cosmological Constant Redshift Fraction of mass to close Universe Relative strength of Cosmological Constant Distance ‘Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant’, Riess et al, 1998 Astronomical Journal v116 1009

29. Gravity Vs Cosmological Constant ‘Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant’, Riess et al, 1998 Astronomical Journal v116 1009

30. Expansion Age of the Universe

31. Reiss et al Conclusions Dark Force / Cosmological Constant positive (99.7% likely) Expansion is accelerating (99.5% likely) Universe is flat Expansion Age of the Universe 14.2 ±1.5 Gyr These are reinforced by further observations

32. Ages of Objects in the Universe These are all very consistent – a good sign!

33. Cosmology Summary The Universe was hot, dense and expanded –We observe galaxy redshifts –Assuming we are not at center implies expansion –Expansion Age is consistent with other ages –Cosmic microwave background, element abundances and evolution are integrated into Big Bang Universe will probably expand forever

34. Before the Big Bang - Inflation Why is the Universe so uniform? It stretched very early on

35. Origin of the Universe Before the Big Bang Idea: Universe Started as a Random Quantum Event –Universe appeared from nothing – net energy is zero –‘Early’ Universe did not have time as a dimension –There is no ‘before’ Idea: Universe properties initially unspecified, but the Universe selects for properties that lead to life (“Life of the Cosmos” by Smolin) There is not a well established theory for before Inflation / Big Bang