Age, Evolution, and Size of the Cosmos Szydagis and Lunin

2 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!

3 History of the Universe The Big Bang Very Hot Universe (< s) – quantum gravity – Inflation Hot Universe (< 1000s) – Formation of baryons – Neutrino decoupling Recombination ( years) Formation of stars (~ 1 bn years) 3 – Grand Unification – Baryon asymmetry – e + /e - annihilation – Primordial nucleosynthesis

4 The Big Bang 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 0 seconds Infinity Time Temperature Energy

5 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 s Kelvin eV

6 End of the GUT epoch and Inflation The strong, weak, and electromagnetic interactions are unified into one force (the Grand Unification Epoch) s Kelvin eV

7 End of the GUT epoch and Inflation 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) s Kelvin eV

8 End of the GUT epoch and Inflation 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 s Kelvin eV

9 Formation of baryons Baryons consist of 3 quarks, mesons: quark + antiquark s K 10 8 eV

10 Formation of baryons Baryons consist of 3 quarks, mesons: quark + antiquark We see matter, but very little antimatter. The symmetry between the two was broken during baryogenesis ( 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) After second quarks became confined within baryons and mesons s K 10 8 eV

11 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 1 s K 10 6 eV

12 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 10 9 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 s K 10 6 eV

13 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 He (25%), D (0.01%), Li ( ), etc s 10 8 K 10 4 eV

14 Recombination Nuclei and electrons bind to form atoms. Transparent Universe (end of the “Dark Ages”) CMB consists of photons produced at recombination years 4000 K 0.3 eV

15 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) years 4000 K 0.3 eV

16 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 1 billion years 18 K / -255 °C eV

17 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 < 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

18 Content of the Universe Dark energy/matter/radiation fractions change with time 18

19 The size of the Universe Distance to the Sun is 1.5 x m Distance to the nearest star ~1pc = 3 x m = 3.3 ly The size of a galaxy 10 4 pc The size of a galaxy cluster 10 6 pc Universe is homogeneous & isotropic above 10 8 pc The size of the visible Universe is pc The size of the full Universe is UNKNOWN. The Universe may be finite or infinite. 19

20 The visible Universe The radius visible U. is 14 x 10 9 pc or 46 x 10 9 light years The naive radius of the entire Universe is 13.8 x 10 9 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 time larger that the observable part. 20

21 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 ed to you. 21