Why does time only ever move in one direction? We talk to philosophers of physics Jeremy Butterfield and David Wallace, as well as the eminent Roger Penrose about the puzzle time poses to physicists and what it has to do with the Big Bang and the second law of thermodynamics.
Traditionally, observers play no special role in physics. Like bird watchers in a perfect hide, we observe the outcome of experiments, or gaze at the stars through our telescopes, taking no part in the action. Modern physics, however, tells a different story ... find out more with these articles and videos.