A Matter of Time

The nature of time is an age-old conundrum for physicists, philosophers, biologists and theologians. The Newtonian picture of time—a kind of cosmic clock that ticks off time in a manner that applies identically to everyone and everything—tightly aligns with our experience. But with special and general relativity, Einstein showed the fallacy inherent in experience: the rate at which time elapses depends on circumstance and environment. These discoveries raise even more basic, long-standing puzzles: What is time? Is it a fundamental feature of reality or something we humans impose on experience? Does time come into existence with the universe or does it transcend it? Why does time exist at all?