Astronomy 113 Dr. Joseph E. Pesce, Ph.D. The Big Bang & Matter Cosmology ³The study of the origins, structure, and evolution of the universe ³Key moments: ²Einstein General Theory of Relativity ²Hubble s observation of expanding universe 17-2 Olber s Paradox ³A simple question: Why is the sky at night dark? You are here 17-3 ³Everything is the same for a long way in all directions Assumptions ³Assumption: the universe is infinitely big ³Assumption: the universe is infinitely old ³Assumption: the universe is uniform 17-4 17-5 Olber s Paradox ³If the universe is infinitely large and uniform, why is the night sky not bright? You are here ³Every sight line will eventually hit a star 1
17-6 The Answer ³The universe can t be infinitely large and old Cosmological Principle: 17-7 Definitions ³Universe is Isotropic & Homogenous ³We are not in a special place Isotropic: the universe is the same in all directions ³There s no preferred direction Homogenous: At the largest scales, the universe is uniform; pretty much the same everywhere; same physical concepts apply Expansion & Big Bang Hubble s Law: v r = H o * D 17-8 ³Universe expanding so must have been smaller, more dense in past ³George Gamow proposes an initial explosion: The Big Bang ³ 1/H o gives age of universe = 13.74 Billion years old (confirmed independently) ³ Redshift: space stretches as photon flies through it = stretching redshift Expansion & Big Bang Hubble s Law: v r = H o * D ³Demonstration 17-9 17-11 Alternate Theories ³Steady State Model of Fred Hoyle, Herman Bondi, and Tom Gold ³Universe infinitely big and old, expands forever, matter constantly being created ²Coming from jets in AGN (in some views) ³Big Bang ironically name by Hoyle 2
4/20/18 17-12 17-13 Evidence for Big Bang ³Roll time back: universe begins as an extremely hot (1012 K) singularity ³High-energy radiation field ³As universe expands, radiation cools ³Radiation should permeate entire universe, even today ³Cosmic Microwave Background (CMB) radiation Detection of CMB ³Arno Penzias & Robert Wilson, Bell Labs (Nobel Prize) ³CMB at 2.74K ³Isotropic and smooth Consistent with Big Bang but NOT Steady State 17-14 17-15 Detection of CMB Isotropy Problem ³To be as smooth as the CMB is, the parts of the universe had to communicate with each other ³But universe is too big for this to be possible 13 Billion ly 26 Billion ly 17-16 17-18 Inflation ³Solution to Isotropy problem is inflation ³10-35 seconds after Big Bang, universe expanded 1050 orders of magnitude (atom to grapefruit) ²The inflationary epoch ²Somewhat strange, but related to dark energy Unification of Forces ³Four fundamental forces today ²Gravitation (dominant today, but VERY weak. Operates over larger scales than others) ²Electro-magnetic ²Strong nuclear (holds protons & neutrons together) ²Weak nuclear (important in radioactive decay) ³Were combined into one at beginning ²During Planck time (0 10-43 seconds after BB) 3
Post Big Bang Timeline 17-19 ³ Planck time (0 10-43 seconds after BB) ³10-43 s (T=10 32 K): Gravity freezes out ³10-35 s (T=10 27 K): Strong force freezes out ³10-35 -10-24 s: Inflation of universe by 10 50 ³10-12 s (T=10 15 K): EM/Weak forces separate ³10-6 s (T=10 13 K): Protons & neutrons can exist Matter/Antimatter Pair Production Pair Annihilation ³For T < 1s: matter/antimatter co-exist ³There should be equal matter and antimatter, annihilating each other. But not the case ³1 EXTRA particle of matter for every billion particles of antimatter ³Good for us! 17-20 Timeline Continues 17-21 ³T = 1 3 minutes: nuclei form, destroyed by gamma-rays ³After T = 3 minutes, Temp too cool for fuse nuclei ²H, He, Li, Be formed ³T < 300,000 years: atoms ionized by photons; only nuclei survive: RADIATION DOMINATED ³T > 300,000 years: atoms can form: MATTER DOMINATED UNIVERSE (still more radiation than matter) Decoupling 17-22 ³T=300,000 years Transition called: Decoupling (Temp = 3,000) ³T < 300,000 yrs: plasma only ³T > 300,000 yrs: H atoms form, universe becomes transparent ² Era of Recombination ²CMB is Fossil of this period ²We can t see further back in time (prior universe is opaque) 17-23 17-24 ³Then what? ²Stars form ²Galaxies form q Where do blackholes come in? ³All happens very soon after decoupling ³Galaxies seem to be made up of small pieces Structures Energy Budget of Universe 4
Age of the Universe ³Related to Hubble s Constant (1/H ~ age) 17-25 ² Must be at least 10,000 yrs old (tree rings) ² Must be at least 200 million yrs old (Cepheid light travel time) ² Must be at least 4.6 billion yrs old (meteor dates) ² Must be at least 10 billion yrs old (redshifts of quasars; globular cluster ages) Thank You! ³Measured accurately and with multiple methods as: 13.74 billion years old 5