Is there any evidence that the Universe was very hot and dense

in the distant past as predicted by the Big Bang model of the

expanding Universe? This lecture examines observational tests

of the Big Bang Model. We have already covered expansion in the

previous lecture. Today we look at Primordial Nucleosynthesis, the creation

of light elements from fusion during the first 3-4 minutes of the

hot phases of the Big Bang, and the Cosmic Background Radiation, the relic

blackbody radiation remaining from when the Universe became transparent

to light 300,000 years after the Big Bang. Both predictions of the Big

Bang Model have been spectacularly confirmed by observations of the

present-day Universe. These give us confidence that the Big Bang, in

broad outline, is the correct physical model of our expanding Universe.

Recorded 2006 February 28 in 1008 Evans Laboratory on the Columbus campus

of The Ohio State University.