What is time?

Reviews of Lee Smolin’s Time Reborn. See especially TensersTime Regained!, and Resetting the Clocks, Smolin explains: “I used to believe in the essential unreality of time. Indeed, I went into physics because as an adolescent I yearned to exchange the time-bound, human world, which I saw as ugly and inhospitable, for a world of pure, timeless truth…. I no longer believe that time is unreal. In fact I have swung to the opposite view: Not only is time real, but nothing we know or experience gets closer to the heart of nature than the reality of time.” Even the laws of nature, Smolin says, are in time and change over time.