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Chapter 17 Cosmology and Big Bang

Chapter 17 Cosmology and Big Bang. 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

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Chapter 17 Cosmology and Big Bang

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  1. Chapter 17Cosmology and Big Bang

  2. 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. • Problems with the Big Bang model and solutions.

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

  4. Hubble Law 1931 V = H d 108 ly Fig. 16-27b, p.331

  5. Basis of Big Bang Model Fact • Universe is expanding. The faster moving galaxies are the farthest away. • 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.

  6. 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

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

  8. 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. Fig. 18-1, p.365

  9. Big Bang Model Fig. 18-6, p.368

  10. Fig. 18-7, p.368

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

  12. 17.2 The Expanding Universe The same analogy can be used to explain thecosmological redshift:

  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

  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(cm)= 0.29/ºK; • For 3ºK, λmax ~0.1 cm = 1 mm. Microwave.

  15. At 3,000ºK the universe became transparent and has cooled now to about 3ºK. 4x105 years Now Fig. 19-6, p.394

  16. Discoverers of Microwave Background Arno Penzias and Robert Wilson Won Nobel prize in 1978 Fig. 19-3, p.393

  17. COBE 1989 Measured microwave background The new satellite is WMAP Fig. 19-4, p.393

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

  19. Microwave background distribution in space Temperature variation in the micro (10-6) Kelvin range Or 1 part per million. At 1 part per 100,000 Universe is very smooth. These variations were the seeds of galaxies Fig. 19-12b, p.398

  20. At the beginning only quarks and leptons existed. Next hydrogen and helium got formed. Fig. 19-13, p.400

  21. Big Bang predictions He / H = 25% and D / H = 0.005% Ratios measured are as predicted. Fig. 19-17, p.402

  22. 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 almost velocity of light. • ~400,000 years – universe becomes transparent. • A few billion years – galaxies start to form.

  23. Fred Hoyle He coined the words Big Bang Fig. 19-2, p.392

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

  25. 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).

  26. Is the Universe FLAT, that is Ω = 1. Ω = ρ/ρc. ρc = 3 H²/8пG = 4 × 10-30 g/cm³. Boomerang measured the flatness of the Universe and it is flat, ie Ω = 1. Fig. 19-10, p.396

  27. Critical density Fig. 18-21, p.378

  28. Are we at the center of the Universe? Small Doppler shift of the microwave background tells us we are not at the center! But not too far away either.

  29. 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 • 4×105 years Universe became transparent at 3,000ºK when p + e  H. • Original black holes gathered material that became galaxies.

  30. Big Bang Problems • Uniformity of microwave background (Horizon problem) • Universe at critical density (Flatness problem) Ω = 1. • Homogeneity problem – not very homogeneous • Why are there more protons than antiprotons. • First two problems are solved by Inflationary Model.

  31. Inflationary theory predicts Ω = 1 and uniform microwave background Fig. 19-20, p.404

  32. Inflationary Universe • Very rapid expansion at about 10-35 second by a factor of 1050!!! • Universe initially was very small so uniform background of microwave is no more a problem. • Very rapid expansion also flattens the universe (Ω=1). Just like the surface of a large balloon looks flat.

  33. 17.7 Cosmic Inflation Inflation would solve both thehorizonand theflatnessproblems. This diagram shows how the flatness problem is solved – after the inflation the need to be very close to the critical density is much more easily met.

  34. Deviation from the Big Bang • Is v = H d valid at large distances? • How do we measure distances to galaxies? • Cepheid variable stars. • Type 1A supernova

  35. 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 luminosity. • A good method to measure distances. All Type 1a supernovae have the same absolute magnitude.

  36. 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. Fig. 18-18, p.376

  37. Supernovae Type1a velocities Edge of the universe

  38. 17.4 The Fate of the Cosmos However, when we look at the data, we see that it corresponds not to adeceleratinguniverse, but to anacceleratingone.

  39. 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.

  40. 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 73 percent of the total mass energy of the universe. Of the rest, about 23 percent appears to be in the form of another mysterious component, dark matter; while only about 4 percent comprises ordinary matter, those protons, neutrons and electrons that we and the visible part of galaxies are made of.

  41. 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

  42. The Expanding Universe If this expansion is extrapolated backwards in time, all galaxies are seen to originate from a single point in an event called theBig Bang. So, where was theBig Bang? It waseverywhere! No matter where in the Universe we are, we will measure the same relation between recessional velocity and distance, with the same Hubble constant.

  43. Is the Universe a Black Hole? • Black hole size R α Mass (M) • Density = M / V = M / (4/3)πR³ α M / M³ • α 1 / M² • If Universe at critical density (Ω = 1) then universe is a black hole. • Universe started with a quantum blip. • There may be many universes.

  44. Birth of the Universe • The total energy of the Universe is zero (to the accuracy we can measure). • Positive energy is mass and dark energy. • Negative energy is gravity. • Sum is zero! • Universe started with a quantum blip! • There can be other universes!!!

  45. 17.4 The Fate of the Cosmos Type I supernovaecan be used to measure the behavior of distant galaxies. If the expansion of the Universe isdecelerating, as it would if gravity were the only force acting, the farthest galaxies had amore rapidrecessional speed in the past, and will appear as though they were recedingfasterthan Hubble’s law would predict.

  46. The Early Universe The total energy of the universe consists of bothradiationand matter. As the Universe cooled, it went from beingradiation-dominatedto beingmatter-dominated. Dark energybecomes more important as the Universe expands.

  47. 17.8 The Formation of Large-Scale Structure in the Universe Galaxiescould then form around thedark-matter clumps, resulting in the Universe we see.

  48. 17.8 The Formation of Large-Scale Structure in the Universe This figure is the result of simulations of a cold dark matter universe with critical density.

  49. Unresolvedmajor topics • What is dark matter? • What is the mysterious force due to dark energy? • If the Universe started from a hot soup, then the number of protons and anti-protons should be the same. It is not! Why? • Are there intelligent beings in the Universe besides Earth?

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