all of space and all of time exist perpetually. Imagine space-time as a loaf of bread, where every slice represents everything that is happening anywhere in the universe in a specific instant. We humans can move in different directions in space, but we experience the dimension of time only slice by slice as we move through it. If we had the ability to perceive time as we do space, we would be able to hop back and forth through time as if we were getting on and off a train at any station we please.
