Cosmology and the Evolution of the Universe Edwin Hubble, 1929: -almost all galaxies have a redshift -moving away from us -greater distance greater redshift Implications of the Hubble Law: - Universe is changing (getting bigger!) - it is not static, unchanging - Universe had a beginning!! - could not have been expanding forever HUBBLE LAW: v = H o 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 (2014): H o = 70.4 to 74.3 km/s per Mpc Age = 13.25 to 13.98 billion years The Big Bang Model Universe began from a single point - that was extremely dense and hot Cosmic Singularity - "Explosion" of matter and energy (and space and time!) -today, 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 Universe: 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. Universe cools as it expands: Time Temperature 0.01 s 100 billion Kelvin 180 s 1 billion Kelvin 400,000 yrs 3000 Kelvin
2. High energy radiation (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 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? Prediction: 3 Kelvin (1964, Peebles and Dicke, Princeton Univ.) 1989, satellite COBE - accurate measurements of Cosmic Microwave Background - Temperature of Universe: T = 2.725 +/- 0.002 K
Expansion of the Universe: - the space between objects is expanding - objects are not moving through space. Cosmological 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 Fate of the Universe: 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 Energy Three Possible Fates: Fates - based on overall density of universe - need to know total mass - need to know overall size (Ho)
Closed Universe: - expansion will eventually stop - gravity will cause universe to collapse - Universe will end in "Big Crunch" - maybe start again (?) Overall geometric shape of universe is spherical Flat universe: - expands forever, always slowing down - not enough gravity to start collapse - Universe 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. - Flat universe is predicted by current theories. Open Universe: - expands forever, possibly going faster and faster - dark energy overwhelms gravity - Universe 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 10 300 400,000 yrs 1 2 billion years 9 10 billion years Today (14 billion years) EVENT The Planck Time: Nothing is known during this time.? Inflation: Universe goes through period of enormous expansion, grows by factor of Radiation 10 43!! Dominated Production of Matter: quarks and electrons Universe created from extremely hot photons (Primordial Nucleosynthesis Era: 2 H and 4 He created by Fireball) 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 Matter as quasars Dominated Formation of Solar System: Sun and planets Universe form within the Galaxy (4.6 billion years ago) (Transparent) Universe still expanding; Average temperature T = 2.725 K