1

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

2

Chapter 24 Homework

•  Chapter 24: #3

3

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).

4

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)

5

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.

6

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

7

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

8

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 DH = cT where T is time since the Big

Bang •  At epoch of recombination DH 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/ρcrit) 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

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 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.

10

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.

11

Chapter 24: The New Cosmology - III •  Evidence for Cosmological Constant or “Dark Energy”

–  Time-scale Test –  High Redshift Supernovae

Measurements of H0 (various methods) and T0 (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, H0T0 ~ 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 (Ωm = 0.24) and a Dark Energy (ΩΛ = 0.76). Note that ΩT = Ωm + ΩΛ = 1, thus a flat cosmology (k = 1) and consistent with the CMB.

12

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.

13

Chapter 24: The New Cosmology - IV

Time (sec) Temp. (K) What < 10-43 > 1032 Grand unification (Plank epoch) 10-43 1032 Gravity separates 10-43 – 10-35 1032 – 1027 GUTs 10-35 1027 Spontaneous symmetry breaking of strong nuclear force 10-35 – 10-33 1027 – 1026 Inflation (~ e100) 10-33 – 10-12 1026 – 1015 Quarks, e-e+, baryogenesis, particle-antiparticle annihilation 10-12 1015 Weak nuclear force separates 2 x 1012 Quark-Hadron phase transition (p, n, ν form) 10-4 1012 Neutral current interaction maintain proton, neutron equilibrium 3 x 1011 Neutrinos de-couple 1 1010 Neutrons decouple from protons (n/p ~ 1/6) 180 109 Deuterium forms, nucleosynthesis begins, all n go to 4He (23%) 106 3000 Recombination of Hydrogen, formation of microwave background 109 yrs 100 First globular clusters and galaxies form 1010 yrs 3 Present time

Brief History of the Universe

14

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 106 years •  First Galaxies: t ~ 300 x 106 years •  Reionization: 150 < t < 1000 x 106 years •  Solar System: 9 x 109 years •  Dark Ages II: 1014 years

15

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.

16

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 cutting-edge scientific research.

17

Chapter 24 Homework

•  Chapter 24: #3