Astr 2320 Thurs. May 7, 2015 Today s Topics Chapter 24: New Cosmology Problems with the Standard Model Cosmic Nucleosynthesis Particle Physics Cosmic Inflation Galaxy Formation 1
Chapter 24: #3 Chapter 24 Homework 2
Chapter 24: Cosmology: The Big Bang and the History of the Universe The Primeval Fireball At Early Times Universe Must Have Been Hot and Dense Hoyle Coined Name: The Big Bang At Early Times Universe Was Ionized and Opaque As it Expands it Cools and Hydrogen will Recombine Epoch of Recombination Blackbody at T ~ 10,000 K Redshift to Present Predicts Microwave Emission Great successes of the Big Bang model has been the prediction of the microwave background and the predicted He abundance (see below). 3
Chapter 24: Cosmology: The Big Bang and the History of the Universe Primordial Nucleosynthesis At Earliest Times Universe was so Hot Only Elementry Particles Existed Neutrons Form but Decay into Protons and Electrons Nucleosynthesis Occurs He forms plus small amounts of Li, Be, B After He forms (no more neutrons) the cooling universe is too cool to form heavy elements The amount of He and Light Elements depends sensitively on Proton to Neutron Ratio so Occurs Only Over First Three Minutes Microwave Background Sound Waves at Epoch of Recombination Power Spectrum Provides Strong Constraint on Cosmological Models (see below) 4
Temperature vs. Time Standard Big Bang Model Predicts Temperature vs. Time Note that the temp. is arbitrarily high at the earliest times. Shortly After Recombination the Universe Becomes Matter Dominated. 5
Thermal Spectrum of Microwave Background Big Bang predicts a thermal spectrum for the Microwave Background Exceeding accurate Black Body. Uniform over sky: ΔT/T < 10-5 6
Temperature Fluctuations in the Microwave Background Sound Waves Are Frozen into the Microwave Background at Recombination. Tiny density fluctuations: Δρ/ρ ~ ΔT/T < 10-5 Power Spectrum Provides Precision Test of Cosmological Models 7
Chapter 24: The New Cosmology Problems with the Standard Model Isotropy and Homogeneity Regions of the universe in causal contact have to be separated by less than a horizon scale. Horizon is defined as D H = ct where T is time since the Big Bang At epoch of recombination D H corresponded to only ~ 40 degrees on the sky. Why are regions of microwave background not in causal contact so uniform in T (ΔT/T < 10-5 )? Flatness Density parameter (Ω = ρ/ρ crit ) could have any value but is pretty close to 1, the critical density and resulting in a flat cosmology. Measurement of the acoustic power spectrum requires that we have precisely a flat cosmology (zero curvature). Why is the universe so close to flat? Origin of Structure Origin of the irregularities that grow to form galaxies is unknown 8
Chapter 24: The New Cosmology - II The Cosmic Microwave Background (CMB) provides a sensitive test of cosmological models. The power spectrum of the acoustic signal in the microwave background. The location of the first peak requires that the universe is flat (k = 0). The location of the second and third peak constrain the Baryonic and dark matter density. Good web page: www.background.uchicago.edu/~whu The WMAP satellite provided the first good measurements of the power spectrum of the CMB. The figure shows the amplitude of the temperature fluctuations as a function of angular scale on the sky. The first peak at 200 wave-numbers corresponds to ~ 1.8 deg. This features requires a flat (k = 1) geometry for the universe. 9
Chapter 24: The New Cosmology - II The Cosmic Microwave Background (CMB) provides a sensitive test of cosmological models. The power spectrum of the acoustic signal in the microwave background. The location of the first peak requires that the universe is flat (k = 0). The location of the second and third peak constrain the Baryonic and dark matter density. Good web page: www.background.uchicago.edu/~whu The Plank satellite provided even better measurements of the power spectrum of the CMB. The figure shows the amplitude of the temperature fluctuations as a function of angular scale on the sky. The first peak at 200 wave-numbers corresponds to ~ 1.8 deg. This features requires a flat (k = 1) geometry for the universe. 10
Chapter 24: The New Cosmology - III Evidence for Cosmological Constant or Dark Energy Time-scale Test High Redshift Supernovae Measurements of H 0 (various methods) and T 0 (age of Globular Clusters) in the 1990s showed that the simple, flat, matter-dominated cosmology with Ω =1 was probably ruled out by. That is, H 0 T 0 ~ 0.9 not 2/3. More recent observations of high redshift supernovae (right) have strongly confirmed this. The best fit models require a modest matter density (Ω m = 0.24) and a Dark Energy (Ω Λ = 0.76). Note that Ω T = Ω m + Ω Λ = 1, thus a flat cosmology (k = 1) and consistent with the CMB. 11
Chapter 24: The New Cosmology - III Particle Physics Grand Unification Models (GUTS) Attempt to Unify the Fundamental Forces GUTS: at higher energies the forces become unified. Electricity & Magnetism unified in 19-th century Weak nuclear force and Strong force added in 20-th century Unification of Gravity is focus of current efforts Next generation of particle accelerators can test some predictions of GUTS (e.g., Higgs particle) but cannot test the highest energy predictions. Predictions for the highest energies testable only via the Big Bang Origin of Dark Matter and the Cosmological Constant (Dark Energy) is currently unknown and may only be addressable via observational cosmological. To date, searches for Dark Matter particles in the lab have failed. 12
Chapter 24: The New Cosmology - IV Brief History of the Universe Time (sec) Temp. (K) What < 10-43 > 10 32 Grand unification (Plank epoch) 10-43 10 32 Gravity separates 10-43 10-35 10 32 10 27 GUTs 10-35 10 27 Spontaneous symmetry breaking of strong nuclear force 10-35 10-33 10 27 10 26 Inflation (~ e 100 ) 10-33 10-12 10 26 10 15 Quarks, e-e+, baryogenesis, particle-antiparticle annihilation 10-12 10 15 Weak nuclear force separates 2 x 10 12 Quark-Hadron phase transition (p, n, ν form) 10-4 10 12 Neutral current interaction maintain proton, neutron equilibrium 3 x 10 11 Neutrinos de-couple 1 10 10 Neutrons decouple from protons (n/p ~ 1/6) 180 10 9 Deuterium forms, nucleosynthesis begins, all n go to 4 He (23%) 10 6 3000 Recombination of Hydrogen, formation of microwave background 10 9 yrs 100 First globular clusters and galaxies form 10 10 yrs 3 Present time 13
Chapter 24: The New Cosmology - IV Alternative Cartoon Version Planck Epoch: t < 10-43 sec 4 fundamental forces unified Grand Unification Epoch: 10-43 < t < 10-36 sec Inflationary Epoch: t ~ 10-32 sec Quark & Higgs Epoch: 10-12 < t < 10-6 sec Hadron (P & N) Epoch: 10-6 < t < 1 sec. Annihilation Epoch: 1 < t < 10 sec. Nucleosynthesis: 3 < t < 20 min. Matter Dominates: 70,000 years Recombination: t = 377,000 years Dark Ages: 150 < t < 800 x 10 6 years First Galaxies: t ~ 300 x 10 6 years Reionization: 150 < t < 1000 x 10 6 years Solar System: 9 x 10 9 years Dark Ages II: 10 14 years 14
Chapter 24: The New Cosmology - V Cosmic Inflation: Energy is injected into the universe by the decay of GUTS particles (Axion?). This inflates the universe (faster than the speed of light) smoothing out irregularities and solving the horizon problem and the flatness problem. 15
Chapter 24: The New Cosmology - VI Galaxy Formation The standard Big Bang model provides no explanation for the origin or the initial fluctuations that grow to form galaxies. Inflation may provide this via quantum mechanical fluctuations. They provide the required slope for the power spectrum and would be inflated to macroscopic size to then grow via gravity. This is an active topic for current theoretical research. Summary Inflationary model provides the best explanation for problems with the standard Big Bang model. It may ultimately prove incomplete as well but it provides the context within which new ideas are formulated and tested. This is the nature of cuttingedge scientific research. 16
Chapter 24: #3 Chapter 24 Homework 17