COSMOLOGY

1. COSMOLOGY How the Universe got started. • The Big Bang Model • Basis of the Big Bang model v = H d • Other supporting evidence • Consequences of the Big Bang model • Universe is finite. Yes -- Quasars • Original heat – microwave background. 2.7ºK microwave observed. • He/H=0.25 and D/H ratio=0.01% observed as predicted. Cosmology

2. Doppler shifted spectra of galaxies Cosmology Fig. 18-4, p.367

3. V = H d 108 ly Cosmology Fig. 16-27b, p.331

4. v = H d Cosmology Fig. 18-5, p.368

5. Edwin Hubble Hubble Law v = H d H ~ 70 km/s/Mpc H ~ 21.5 km/s/Mly Cosmology Fig. 16-5, p.317

6. Basis of Big Bang Model Fact • Universe is expanding • v = H d • Time = d / v = d / H d = 1/H independent of which two galactic clusters we look. • About 14 billion years ago (1/H) the Universe was very small and very hot and has been expanding ever since. Cosmology

7. Age of Universe = 1 / H Time (age) = 1/H = 1 / 21.5 km/s/Mly 1 Mly = 106 ly × 9.46 × 1012 km/ly = 9.46 × 1018 km Time = [1/21.5km/s/Mly] × 9.46 × 1018 km/Mly = 4.4 × 1017 sec. = 4.4 × 1017 sec / 3.15 × 107 sec/yr = 1.4 × 1010 yr OR 14 billion years Cosmology

8. Other supporting evidence of Big Bang model. Why is the sky dark at night If Universe was infinite in size, then the night sky should not be black. This was known as Olbers’ paradox. Cosmology p.364

9. Olbers’ paradox Brightness at night is proportional (α) to sum of all spheres. Intensity from each sphere α 1/R². Number of stars on each sphere is α 4πR². Total is sum (1/R²)×4πR² is infinite Therefore size is not infinite. Cosmology Fig. 18-1, p.365

10. Big Bang Model Cosmology Fig. 18-6, p.368

11. Cosmology Fig. 18-7, p.368

12. Each photon gets stretched Cosmology Fig. 18-9, p.369

13. Consequences of Cosmology • Universe is finite in size. • Where is the remnants of the original heat? • Universe has finite age Time = d / v Time = d / Hd = 1/H Distribution of quasars Or distance in billion ly Cosmology

14. Original Heat • Expansion is cooling • Universe got transparent when protons and electrons formed hydrogen. The temperature for this to occur is 3,000ºK. • Universe has expanded by a factor of about 100,000 since then. • Universe has cooled to ~ 3ºK. • The λmax(nm)= 2,900,000/ºK; For 3ºK, λmax ~1,000,000 nm = 1 mm. Microwave. Cosmology

15. Universe has expanded and cooled to 2.7ºK. The microwave background is the remains of the original heat COBE satellite results Cosmology Fig. 19-5, p.393

16. How do we measure distances? • To know more about Cosmology we need to measure distances to the edge of the Universe. • Need to obtain absolute luminosity • Measure apparent luminosity • Calculate distance • In galaxies that we observe individual stars, use Cepheid variables. • For far away galaxies where stars are not resolved, use Type 1A supernova. Cosmology

17. Cepheid variable star in M100 Cosmology Fig. 18-13, p.373

18. Cepheid variable stars Absolute magnitude M and apparent magnitude m are related by distance. m – M = 5logd – 5 d in parsec. Cosmology Fig. 18-11, p.372

19. HST photo of M100 Distance measured by Cepheid variable star Cosmology Fig. 18-14, p.374

20. Type 1ASupernova • A double star system where one star has shed enough mass to become a 1.4M white dwarf. • If the second star is close to the first star and becomes a red giant, mass flows from the red giant to the white dwarf. • When the mass of the white dwarf exceeds 1.4M the star goes supernova of Type 1A. All Type 1A supernovae have the same absolute magnitude. Cosmology

21. Type 1A supernovae Binary star system where one star is white dwarf. When matter from other star flows to white dwarf and exceeds 1.4 M star becomes Type 1A supernova. Cosmology Fig. 18-18, p.376

22. Type 1A supernova Cosmology Fig. 18-27, p.384

23. Hubble diagram from Cepheid variable stars To 65 million ly. Hubble diagram up to 1.3 billion ly. 0.1 size of universe Cosmology Fig. 18-16, p.375

24. Supernovae Type1a velocities Edge of the universe Cosmology

25. Supernova data Cosmology

26. Deviation from Hubble Law • The edge of the universe is expanding faster than Hubble Law predicts. • There must be a force that is pushing the edge out. • This force is the result of an unknown energy called DARK ENERGY. Cosmology

27. Dark Energy • Albert Einstein initially thought that the universe was static: that it neither expanded nor shrank. When his own Theory of General Relativity clearly showed that the universe should expand or contract, Einstein chose to introduce a new ingredient into his theory. His "cosmological constant" represented a mass density of empty space that drove the universe to expand at an ever-increasing rate. • When in 1929 Edwin Hubble proved that the universe is in fact expanding, Einstein repudiated his cosmological constant, calling it "the greatest blunder of my life." Then, almost a century later, physicists resurrected the cosmological constant in a variant called dark energy. In 1998, observations of very distant supernovae demonstrated that the universe is expanding at an accelerating rate. This accelerating expansion seemed to be explicable only by the presence of a new component of the universe, a "dark energy," representing some 70 percent of the total mass of the universe. Of the rest, about 25 percent appears to be in the form of another mysterious component, dark matter; while only about 5 percent comprises ordinary matter, those quarks, protons, neutrons and electrons that we and the galaxies are made of. Cosmology

28. Big Bang Model • Universe started about 14 billion years ago with a big explosion. • At the beginning of time, universe was small in size and very hot. Expansion is cooling. • Edge of Universe expands at velocity of light. • 1,000,000 years – universe becomes transparent. • A few billion year – galaxies start to form. Cosmology

29. Cosmology

30. Early Universe • Very Hot at the beginning. 1032ºK • Expansion is cooling • Up to 10-6 second quark lepton soup. • 10-6 sec to 1 sec form protons, electron, etc. • 1 sec to 3 min nuclear synthesis D, He, Li, etc • 106 years Universe became transparent at 3,000ºK when p + e  H • Original black holes gathered material that became galaxies. Cosmology

31. Density of the Universe ΩM=ρ/ρc • Critical density between open and closed universe. • ρc = 3 H²/8пG = 4 × 10-30 g/cm³. • If the universe density is above ρc the universe expansion will stop and the universe will contract into a big crunch. • If the universe density is equal or less than ρc then the universe will expand forever. • Define ΩM = ρ/ ρc. Ω = 1 = ΩM + ΩΛ • Λ is the fudge factor inserted by Einstein so Universe will not collapse under gravity. • Energy of universe has two parts mass (M) and dark energy (Λ). Cosmology

32. Critical density Cosmology Fig. 18-21, p.378

33. Problems with Big Bang • Uniformity of microwave background (Horizon problem). One side of the universe has no communication with the other side. • Universe is very close to critical density Ω = 1. (Flatness problem). Why? • Homogeneity problem (not very homogeneous). • Why are there more protons than antiprotons. Cosmology

34. Cosmological Principle Laws of physics same always. Universe is both homogeneous and isotropic. Homogeneous but not isotropic. Homogeneous and isotropic. Cosmology Fig. 18-19, p.377

35. WMAP WilkinsonMicrowave Anisotropy Probe Universe is composed of the following mixture • 4.4±0.4% normal baryonic matter (e.g. atoms) • 23±4% dark matter • 73±4% dark energy • Most dark matter is cold • Neutrinos make up less than 0.75% of dark matter Cosmology