What are space and time? To begin our exploration of the evolving

Universe, we must first understand what we mean by space and time.

This lecture contrasts the Newtonian view of the World, with its

absolute space and absolute time, with that of Einstein, who showed

that space and time were not absolute but relative constructs, and

that only spacetime, unified by light, was independent of the observer.

This requires such non-intuitive notions as the speed of light being

the same for all observers regardless of their motion, and that

observers moving relative to each other will agree on the same physical

laws and speed of light, but disagree on lengths, times, masses, etc.

measured by applying those laws. This sets the stage for Einstein's

revision of the Law of Gravity, General Relativity, which we will

review in the following lecture.

Recorded 2006 February 20 in 1008 Evans Laboratory on the Columbus campus

of The Ohio State University.