Plato argued that time is constant – it’s life that’s the illusion. Galileo shrugged over the philos-ophy of time and figured out how to plot it on a graph so he could get on with the important physics. Albert Einstein said that time is just another dimension, a fourth one to go along with the up-down, side-side, forward-back we move through every day. Our understanding of time, Einstein said, is based on its relationship to our environment. Weirdly, the faster you travel, the slower time moves. The most radical interpretation of his theory: Past, present, and future are merely figments of our imagination, constructs built by our brains so that everything doesn’t seem to happen at once.
Einstein’s conception of unified spacetime works better on graph paper than in the real world. Time isn’t like those other dimensions – for one thing, we move only one way within it. “What’s needed is not to make the notion of time and general relativity work or to go back to the notion of absolute time, but to invent something radically new,” says Lee Smolin, a physicist at the Perimeter Institute in Waterloo, Ontario. Somebody is going to get it right eventually. It’ll just take time.