What are the implications of Relativity for the Universe? This lecture

introduces the Cosmological Principle, which states that the Universe is

Homogeneous and Isotropic on Large Scales. Applying this to his

then-new General Relativyt, Einstein got a surprise: the Universe must

either expand or contract in response to all the matter/energy that

fills it, something not observed in 1917. To attempt to stabilize the

Universe, he introduced a Cosmological Constant (Lambda), that was to

prove his greatest blunder. Subsequent theoretical and observational

work was to establish that the Universe is indeed expanding

systematically, if you look on scales large enough (the scale of

galaxies). We will review observational evidence for the large-scale

Homogeneity and Isotropy of the Universe, Einstein's brilliant conjecture,

and see how the Cosmological Constant maybe wasn't such a blunder after

all, as it has recently made a comeback of sorts. We'll explore these

themes in greater detail in subsequent lectures.

Recorded 2006 February 22 in 1008 Evans Laboratory on the Columbus campus

of The Ohio State University.