Between the past and the future lies the present. Don't even try to [guess] exactly where it is, the effort is useless. There is no pin point, no dot on a line on which we may place a marker and declare boldly, "Here is now!" Sure, we could dive into the physics of it, and I'm sure a thousand different experts would yield a thousand different answers. But from a human point of view, here and now is just a phrase, nothing more. But just for fun, go ahead. Try it. Try to concentrate on a single instance in time. Put on a piece of music and try to hear only one note while the rest of the piece progresses. Can you remember the measure before? You had better, because in your mind is the only place it exists.

Some memories are so juicy, so vivid, and thick. We can concentrate on one given moment and travel to the past. The human mind is capable of pin pointing a time period and rendering it in your mind. Sometimes the memory is so inveigling that we lose track of our surroundings, returning us into the past.