How to think about... Time

2019-03-15 08:10:01

Kyoshino/Getty By Richard Webb NEVER trust a physicist to tell you the time, says Marina Cortes at the University of Lisbon in Portugal. “Physics has a slightly different idea about what time is.” We used to think we had it nailed: time was the tick-tock of a clock somewhere outside the universe against which all processes within it could be measured. This appealing, intuitive idea of an absolute time underpins things like Newton’s classical laws of motion, and even the distinctly non-intuitive workings of quantum equations, our best description of the nitty-gritty of reality. Never mind where these external readings of time would come from, Einstein’s theories of relativity blew away the whole idea. Einstein showed that space and time are, well, relative. Both are part of a unified space-time that is warped by both gravity and motion so that no two observers can ever fully agree on what happened when. The discrepancies are imperceptible to us because we live our whole lives in roughly the same gravitational field and at roughly the same low speeds. We are deceived into thinking time is absolute by an accident of circumstance, says physicist Carlo Rovelli at Aix-Marseille University in France, author of The Order of Time . “In our experience, time passes at the same rate. But this is only true in the non-relativistic approximation in which we live.” So rule one in thinking clearly about time: