Cosmology and the Evolution of the Edwin Hubble, 1929: -almost all galaxies have a redshift -moving away from us -exceptions in Local Group -with distance measurements - found a relationship greater distance greater redshift Implications of the Hubble Law: - is changing (getting bigger!) - it is not static, unchanging - had a beginning!! - could not have been expanding forever HUBBLE LAW: v = Ho r v = velocity (speed); r = distance Rate of expansion: H o = Hubble constant (slope of line) The Hubble Constant tells us: - Size of observable universe largest redshift = largest distance - Age of universe how long ago everything was together - Fate of universe what will happen in future Most accurate measurements (2015): H o = 73.5 km/s per Mpc Age = 13.799 ± 0.038 billion years The Big Bang Model began from a single point - that was extremely dense and hot Cosmic Singularity - "Explosion" of matter and energy (and space and time!) -today, space is still expanding - properties of universe change with time - had different conditions in the past - will have diff. conditions in future - ultimate fate is unknown The Early : Initially was very HOT! - Hot enough for Hydrogen fusion everywhere in space! - explains why 25% of universe is Helium Basic Principles of Big Bang Model 1. cools as it expands: Time Temperature 0.01 s 100 billion Kelvin 180 s 1 billion Kelvin 380,000 yrs 3000 Kelvin
2. Initially, the universe contained only photons (no matter) - High energy photons create matter E = m c 2 Gamma Rays electron positron 3. Energy of radiation (photons) depends on temperature of universe - As universe expands and cools - radiation loses energy - universe is a blackbody Prediction: 3 Kelvin (1964, Peebles and Dicke, Princeton Univ.) 1964, A. Penzias and R. Wilson (Bell Labs) -built antenna for satellite communications -detected "noise" in all directions -background noise corresponds to temperature of 3 Kelvin! Energy leftover from the BIG BANG!!! Cosmic Microwave Background (CMB) PREDICTION: According to Big Bang Model: What is temperature of universe TODAY? 1989, satellite COBE - accurate measurements of Cosmic Microwave Background - Temperature of : T = 2.725 +/- 0.002 K
Expansion of the : - the space between objects is expanding - objects are not moving through space. Cosmological Principle: - there is no center, no edge - every location appears to be at center - same at every location (large scales) Homogeneous - same appearance in every direction Isotropic Clusters, Superclusters, Voids - origins should be seen in the CMB - 1992, temp fluctuations of 0.0002 K - seeds of large scale structure 1992 2003 2015 Surprising Discovery in 1998: - rate of expansion is increasing! - previously thought that gravity would slow expansion over time - what can overcome affects of gravity? - repulsive, anti-gravity force - Dark Energy
Fate of the : Three Possible Fates: - based on overall density of universe - need to know total mass - need to know overall size (H o ) Closed : - expansion will eventually stop - gravity will cause universe to collapse - will end in "Big Crunch" - maybe start again (?) Flat universe: - expands forever, always slowing down - not enough gravity to start collapse - will end in Cold Death - all forms of energy becomes evenly distributed in space. - everywhere in universe is same temperature -close to absolute zero Overall shape of universe is flat. Overall geometric shape of universe is spherical - Flat universe is predicted by current theories. Open : - expands forever, possibly going faster and faster - dark energy overwhelms gravity - will end in Big Rip - dark energy overwhelms all other forces. - expansion will accelerate so much, all matter will get ripped apart Overall shape of universe is hyperbolic. TIME 0 10-43 10-35 10-32 10-8 10 10 300 380,000 yrs 1 2 billion years 9 10 billion years Today (14 billion years) EVENT The Planck Time: Nothing is known during this time. Inflation: goes through period of enormous expansion, grows by factor of 10 43!! Production of Matter: quarks and electrons created from extremely hot photons Nucleosynthesis Era: 2 H and 4 He created by fusion reactions throughout the universe Era of Recombination: Electrons combine with nuclei to form atoms; (T = 3000 K), space is now transparent Formation of Galaxies: Young galaxies seen as quasars Formation of Solar System: Sun and planets form within the Galaxy (4.6 billion years ago) still expanding; Average temperature T = 2.725 K? Radiation Dominated (Primordial Fireball) Matter Dominated (Transparent)