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Age, Evolution, and Size of the Cosmos 02.18.2015 Szydagis and Lunin The Age of the Universe • The Universe is 13.8 billion years old. • How do we know this? • The most important ingredient is the Hubble's parameter • Various independent methods – Type Ia supernova explosions – Cosmic Microwave Background (WMAP, Planck) – Crude lower bound: age of oldest stars • All estimates agree within the uncertainties! 2 History of the Universe • The Big Bang • Very Hot Universe (< 10-10s) – quantum gravity – Grand Unification – Inflation – Baryon asymmetry • Hot Universe (< 1000s) 3 – Formation of baryons – e+/e- annihilation – Neutrino decoupling – Primordial nucleosynthesis • Recombination (380 000 years) • Formation of stars (~ 1 bn years) 3 The Big Bang 0 seconds Time Temperature Infinity Infinity Energy • The existing physical theories break down. • Formal application of GR: naked singularity • New physics is needed to resolve the singularity String theory? Loop quantum gravity? • What happened before the Big Bang? traditional answer: there was no time speculative ideas: Big Bounce • Big Bang is one of the greatest challenges in physics 4 -43 10 s 32 10 Kelvin 28 10 eV Quantum Gravity • All forces are carried by particles (photons, gluons, W/Z) • Gravity must be carried by gravitons. Quantum effects are small at low energies, but they dominate when field is strong. • QG is still being developed (string theory, loop gravity, etc) • Main applications of QG: Early Universe, black holes. • Dynamics at this stage determines all subsequent evolution. 5 -34 End of the GUT epoch and Inflation 10 s 27 10 Kelvin 23 10 eV • The strong, weak, and electromagnetic interactions are unified into one force (the Grand Unification Epoch). 6 -34 End of the GUT epoch and Inflation 10 s 27 10 Kelvin 23 10 eV • The strong, weak, and electromagnetic interactions are unified into one force (the Grand Unification Epoch). • The unification requires a doubling of the number of particles at high energies (supersymmetry). 7 -34 End of the GUT epoch and Inflation 10 s 27 10 Kelvin 23 10 eV • The strong, weak, and electromagnetic interactions are unified into one force (the Grand Unification Epoch). • The unification requires a doubling of the number of particles at high energies (supersymmetry) • After individual forces emerged, the Universe went through a very rapid expansion (inflation). • The entire VISIBLE Universe emerged from a TINY PART of the Cosmos, this explains homogeneity and flatness seen in CMB. • Inflation predicts multiverses with different physical properties. 8 -5 10 s 12 10 K 8 10 eV Formation of baryons • Baryons consist of 3 quarks, mesons: quark + antiquark 9 -5 10 s 12 10 K 8 10 eV Formation of baryons • Baryons consist of 3 quarks, mesons: quark + antiquark • We see matter, but very little antimatter. The symmetry -40 between the two was broken during baryogenesis (10 s) • Free quarks cannot exist (confinement) • In the early Universe, quark and gluons formed a distinct state of matter called quark-gluon plasma (observed at CERN and RHIC) -5 • After 10 second quarks became confined within baryons and mesons. 10 1s 1010 K 106 eV Photons and neutrinos • Neutrinos decouple after 0.2 s (1 MeV) – The ratio n/p is frozen, it sets stage for nucleosynthesis – Neutrinos keep cooling off ONLY due to expansion • Photons are produced in e+/e- annihilation at t < 1s 11 1s 1010 K 106 eV Photons and neutrinos • Neutrinos decouple after 0.2 s (1 MeV) • The ratio n/p is frozen, it sets stage for nucleosynthesis • Neutrinos keep cooling off ONLY due to expansion • Photons are produced in e+/e- annihilation at t < 1s • Only one electron per 109 e+/e- survives • Photons keep cooling off MOSTLY due to expansion, the ratio of photon/neutrino temperatures is set (>1) • Remaining electrons will form atoms during recombination. 12 200 s 8 10 K 4 10 eV Primodial Nuocleosythesis • Stars don't explain He abundance (25% of baryonic matter) – Nuclear reactions: He abundance is related to luminosity – Observations: less than 0.5% of He is formed is stars • Light elements are produced through a chain of nuclear processes involving deuterium and tritium • Complicated equations predict the CORRECT abundances of -10 He (25%), D (0.01%), Li (10 ), etc. 13 380000 years 4000 K 0.3 eV Recombination • Nuclei and electrons bind to form atoms. • Transparent Universe (end of the “Dark Ages”) • CMB consists of photons produced at recombination. 14 380000 years 4000 K 0.3 eV Recombination • Nuclei and electrons bind to form atoms. • Transparent Universe (end of the “Dark Ages”) • CMB consists of photons produced at recombination. • The most accurate info about the early Universe • Continuous improvements (COBE, WMAP, Planck satellites) 15 1 billion years 18 K / -255 °C -3 1.5 10 eV Formation of stars • Cloud of hydrogen collapses due to gravity. • High pressure ignites nuclear reactions. • Heavy elements are produced as star burns, they are dispersed through supernova explosions. • Galaxies and galaxy clusters are formed. • Younger stars and planetary systems are formed – Solar system: 9 bn years after the Big Bang • Life of Earth ~ 3.5 bn years ago (10.3 b.y. after the BB) 16 What drives the expansion of the Universe? • Spacetime tells matter how to move, matter tells spacetime how to curve (J. Wheeler) • Three forms of “matter” (energy) and their domination – Hot matter (radiation & neutrinos) (t < 47 000 years) – Cold matter (baryionic and dark) – Dark energy (t > 10 bn years) • Present breakdown: dark energy (68%), dark matter (27%), ordinary matter (5%), radiation (tiny fraction) 17 Content of the Universe • Dark energy/matter/radiation fractions change with time 18 The size of the Universe 11 • Distance to the Sun is 1.5 x 10 m 16 • Distance to the nearest star ~1pc = 3 x 10 m = 3.3 ly 4 • The size of a galaxy 10 pc 6 • The size of a galaxy cluster 10 pc • Universe is homogeneous & isotropic above 108 pc 10 • The size of the visible Universe is 10 pc • The size of the full Universe is UNKNOWN. • The Universe may be finite or infinite. 19 The visible Universe • The radius visible U. is 14 x 109 pc or 46 x 109 light years • The naive radius of the entire Universe is 13.8 x 109 ly. • Expansion of the Universe: – objects move away after emitting light – law of expansion and age give the size • Cosmic horizon is expanding: new objects enter at the edges. • Inflation: the Universe is at least 1023 time larger that the observable part. 20 Homework • Read the links next to powerpoint version of this talk on the course website syllabus table for Friday • Complete written homework #4, also for Friday. • Additional reading material will be emailed to you. 21