Time’s not a universal quantity. We used to think that it was, we used to think that it was just… there, marching on at the same pace for everyone everywhere. Like a railway track that stretched to infinity. Time was eternal. Now we know that it isn’t. You have to know this – it’s incredibly important. Time’s not a background thing, it’s not an absolute against which everything is measured. It’s dynamic. Active. Wonderful. If you were to travel east very, very quickly, and I stayed here, your time would slow down relative to mine. Time’s very important.
Benedict Cumberbatch in Hawking