“Time” is the most-used noun in the English language, yet some physicists don’t even believe that time is real. In this talk, Sean Carroll will argue that time is real, yet that some aspects of it remain mysterious. Time seems to move forward because entropy increases — the universe was orderly in the past, and grows more disorderly toward the future. Scientists are currently working to puzzle together how increasing entropy explains memory, aging, and why our decisions can affect the future but not the past.