"A monumental work on the flow of time, from the universe's creation to "Now," by the best-selling author of Physics for Future Presidents. "Now" is a simple concept--you're reading this sentence now. Yet a real definition of "now" has eluded even the great Einstein. We know that time stretches and is affected by gravity and velocity. Yet, as eminent physicist Richard A. Muller points out, it is only today that we have all the physics at hand--relativity,...