Time’s endless flow shapes the way we understand the world. Being carried along on a river of time T that only flows in one direction is essential to our understanding of the universe. But what exactly is time, and where does it come from? Recent research is suggesting some surprising new ideas. For more than a century, scientists have treated time as a dimension – a ‘direction of travel’ both similar to and radically different from the three space dimensions. Thanks to Einstein’s theory of general relativity, it’s also clear that space and time are wrapped up together in a complex ‘continuum’ called space-time. In extreme situations, distance in space and the flow of time can be stretched, compressed or even exchanged.
Professor Sean Carroll, author of From Eternity to Here: The Quest for the Ultimate Theory of Time, argues that time isn’t really that hard to understand. “I don’t think it’s a mystery, and I don’t think it’s been a mystery for a very long time,” he explains. “It was a bit simpler back when we had Isaac Newton and time and space were both absolute. Then we would have considered the universe to be made of space and everything in it, and the universe keeps happening over and over again – time is just the label we put on those different versions that happen one after another with things in different positions, a bit like the pages of a book.
“In Einstein’s view there’s actually ‘space-time’, and how an observer slices that space-time into time and space is a little arbitrary,” continues Carroll, the Homewood professor of natural philosophy at Johns Hopkins University. “Different people can look
