Cosmology -- the Origin and Structure of the Universe Cosmological Principle – the Universe appears the same from all directions. There is no preferred location. (The physical laws apply to the whole Universe). Is there a preferred time ?

The Distance – Redshift Relation (Hubble Law) The Distribution of Matter – Large Scale Structure Implications of the finite velocity of light Consequences of star birth and death

Cosmological models -- “world views” How we perceive our Universe and our relation to it Historical models -- geocentric heliocentric galactocentric By mid 20 th century -- 3 models or theories Big Bang -- Father LeMaitre, George Gamow Oscillating Universe Steady State -- Fred Hoyle Early 21 st century – Big Bang cosmology firmly established

Four Fundamental Forces Gravity ~ m1m2/r 2 Large scale structure and motions Electromagnetic ~ 1/r 2 attraction and repulsion Strong (nuclear) -- nuclear binding force Weak (nuclear) force -- nuclear reactions Grand Unified Theory -- GUT Limit to observable Universe Set by c and age of Universe -- 1/H = 4400 Mpc Hubble radius

Standard Big Bang model extrapolating backwards – Universe began in a superdense state of matter and energy Time T = 0 ? From t = 0 to sec Planck time -- GUT Gravity separates At t = sec cooled to K Strong nuclear force separates INFLATION occurs At sec K EM force separates At sec K, gm/cm3, proton, neutrons exist Like neutron star

At 1 sec (IMPORTANT)  +  >< e + + e - (E = mc 2 ) Density 10 5/ cm 3, K This reaction ceases, anti-matter no longer created At 3 minutes fusion occurs from p + and n fusion H  He4 traces of Li, Be, B At 300, 000 yrs temp cooled to 3000 K Recombination occurs p + + e -  atoms Up until this time, Universe was filled with hot, ionized gas – a plasma, the photons and electrons interacted Opaque -- the primordial fireball Now transparent to radiation

Photons – the original BB photons are now fee Predicted by theory to exist but because of expansion cooled or redshifted to 3 K

3 degree background radiation or cosmic microwave background radiation (CMB) Nobel Prize 1978

Subsequent work -- numerous measurements, balloon, satellites COBE WMAP

The Big Bang -- the standard model -- ~14 x 10 9 yrs

The Early Universe – the Hubble Deep Field (HDF) Deepest exposure with HST 10 consecutive days, 342 exposures, Reaching > 30 th mag

Small irregular galaxies - among first objects Glow from first stars ?

Other considerations -- the critical density of matter, finite or infinite ? and the shape of space

Critical Density of the Universe – the required density for a flat Universe not contracting due to gravity Need mass and radiation densities radiation from photons (most from BB but redshifted) 4.6 x kg/m 3 matter or mass --- luminous matter 3.6 x kg/m 3 but mass from rotation curves of galaxies and mass required to bind clusters of galaxies -- 2 – kg/ m3 (dark matter) Luminous matter ~ 10 % of all matter Today matter dominates over radiation

Combined mass density (matter + energy)    Critical density  c = 3 H 2 / 8  G = 9.2 x kg/ m 3 Density parameter  0 =  0 /  c Space Curvature Type Density (  0 ) Spherical positive Closed > 1 Flat flat Flat = 1 Hyperbolic negative Open < 1 Numerous studies + CMB  flat or nearly so +/- 10%

But density due to matter  m /  c = So  m <  0 So missing density ! propose missing density   (dark energy) Einstein’s “cosmological constant”

Type Ia supernovae, the accelerating Universe and dark energy Nobel Prize 2011 Saul Perlmutter Brian Schmidt Adam Reiss

So there are three numbers  m = 0.2 – 0.4 (matter, mostly dark)   = ?  0 ~ 1.0 +/- 10 %

At the beginning of the 21st century: The Universe began in a superdense state; it is flat, expanding, the expansion is accelerating, it is dominated by dark energy, and will expand forever. What about the future ?