It seems the universe began with an explosion Rainer Weiss Newton Free Library February 28, 2008

Churning of the milky ocean Asuras Shankha Vishnu Uchchaisravas Surabhi Vasuk Turtles all the way Mandan mountain churn Devas

Olber’s Paradox Why is the sky dark at night? Night sky in Arizona All lines of sight hit a star

Geometric methods Eratosthenes measurement of Earth’s radius (240BC) Parallax of comet Hyakutake

January July

Distance from intensity Types of stars : the HR diagram Finding more powerful standard “candles” Intensity of star at observer vs distance Intensity ~ 1/distance 2

Henrietta Leavitt at Harvard Smithsonian (~1910) Cepheid variables important Henrietta Leavitt at Harvard Smithsonian (~1910)

Supernova “standard candles” Outshine an entire galaxy for a few days Occur about once every 100 years in a typical galaxy

Spectroscopy of star light Spectrometer placed at output of a telescope provides information about the composition of a distant object. Spectrum of an atom is a unique signature A hydrogen atom on the Earth is the same as one in a distant galaxy

Red (longer wavelength) shift of the spectral lines of atoms with distance Dl/l G ly Ursa Major 0.05 1.0 0.07 1.4 0.13 2.5 0.203 3.96 Corona Borealis Bootes Hydra

Hubble Diagram redshift vs distance Edwin Hubble More distant

Interpretation of the red shift with distance CHARACTERISTICS Dl/l independent of the wavelength does not depend on direction in the sky does not depend on the type of object WHAT IT ISN’T DUE TO Light becoming tired Change in the fundamental constants of nature with distance (and time) DOPPLER INTERPRETATION Stretch or compression of waves by moving away from or toward source One way The other way

Profound implications of the Doppler Interpretation Universal expansion – homogeneous and isotropic Relative velocity proportional to separation There is a beginning when it was very dense The age of the universe is 13.7 G years The expanding universe is a solution in Einstein’s General Relativity

The explosion was hot at the beginning Holmdel, New Jersey antenna used by Penzias and Wilson in measuring noise from the universe (1964-1965) Dicke radiometer Temperature now 3K, 13G yrs ago 10000K

Spectrum of a hot thing --- thermal Planck spectrum

Scale should read 1/wavelength Thermal spectrum curves progressively colder Scale should read 1/wavelength Cosmic background radiation spectrum from COBE (J. Mather, Nobel Prize 2006) Universe was in thermal equilibrium until ~300000 years after the primeval explosion

Thermal equilibrium -- featureless homogeneity and isotropy

COBE sky COBE 7 angle deg 3K 3 milliK 10 microK 10 microK Dipole due to our motion in the universe 3 milliK 10 microK with galaxy in 10 microK WMAP 0.5 angle deg Quantum fluctuations inside the primeval kernel frozen in by dark matter !!!!!

Dark matter (blue), atoms (red) What is it? WMAP modeling results Colliding galaxies W = 1 What is it? Dark matter (blue), atoms (red) Vera Rubin found dark matter in galaxies Galactic cluster

History of the universe (2008)

Large Scale Structure of the Universe Gravitation of dark matter – our version of the churn Sloan survey large scale structure: grown from the seeds of the primeval quantum fluctuations. The population of the blue distance chart from the beginning of the talk. Thank WGBH for “Whisper from Space”