Seasons change, time passes. What would we do without it? Much as we might like to, we cannot rewind or fast forward the tape of our lives. The past is behind us, and the future is yet to come. There is a powerful sense that time flows, and does so at a steady pace, and we assume that it will do this throughout the Universe. The Hands of TimeTime goes only one way; it seems to be asymmetric, or lopsided. This lopsidedness affects many objects and events that we experience in the physical world. Physicists like to call this asymmetry in time 'the arrow of time', meaning a sort of cosmic signpost pointing in a single direction.