Physicist Jim Al-Khalili, Distinguished Professor Emeritus at the University of Surrey, delivers the Annual Sir Thomas Gresham Lecture on what physics actually says about time. He moves from the ancient dispute between Parmenides and Heraclitus through time as a measurable dimension, Laplace's demon and predictability, and the block universe picture in which all moments coexist in spacetime. He covers time dilation with examples from GPS satellites, black holes, and the film Interstellar, then turns to quantum gravity and the Wheeler-DeWitt equation, which contains no time variable at all. The arrow of time gets its own treatment through entropy, card shuffling, the second law, and Loschmidt's paradox, before closing on whether time had a beginning or will have an end. Al-Khalili ends without a final verdict: time is real, he says, but the deepest questions about it remain open.