It's more than some half-baked question from your college days. Time and its "real"-ness are, in fact, major considerations in fields like physics and philosophy. But then, what does that question – Is time real? – even mean? Theoretical physicist Sean Carroll gets down to brass tacks on time, reality, and how we experience both.

Via the PBS series "Closer to Truth." If you're as big a fan of Carroll's lucid explanations as we are, try this on for size.