Why do we remember the past and not the future? What does it mean for time to 'flow? Do we exist in time or does time exist in us? Italian theoretical physicist Carlo Rovelli invites us to consider questions about the nature of time that continue to puzzle physicists and philosophers alike.
Humans have always been obsessed with time and have marked its passage in part by measuring it with ever increasing accuracy, yet its true nature has remained elusive. We all know from our subjective experience that when we are placed on hold while waiting for a representative, even a few minuites feel like eternity, while time appears to hurtle on when we are in the midst of a pleasurable activity...Though physics, philosophy and metaphysics have all grappled with the concept of time, we are still confounded by it.
Is time real or simply a useful measurement of change? Rovelli’s book opens with a discussion of Newton’s idea of absolute 'true time', ticking relentlessly across the universe. This is how most of us still imagine time, though Einstein showed that there is no single 'now' but rather a multitude of 'nows'. Rovelli goes on to consider Aristotle’s belief that what we call 'time' is simply the measurement of change: if nothing changed, time would not exist. Newton chose to disagree. If the universe was to be frozen, time would tick on regardless...Impishly, Einstein asserted that both Aristotle and Newton were right. Aristotle correctly explained that time flows in relation to a before and after; and Newton’s absolute time does indeed exist – but as a special case in Einstein’s 'spacetime' theory of gravity, which treated space and time as one and the same. The riddle of time may ultimately be beyond our 'blurred', Earth-bound comprehension, says Rovelli. All the same, in lucid pages, he manages to bring difficult ideas down a level. Not since the late Stephen Hawking’s A Brief History of Time has there been so genial an integration of physics and philosophy.
Time is a commodity: ours to buy, spend, save, keep, mark or waste. Time has volition: it flies, drags, stands still. The verbs alone suggest that we have always understood time as subjective, something experienced according to individual circumstance ... In 1972, physicists sent a quartet of caesium clocks jetting around the planet in different directions to confirm Einstein’s special relativity. People who live at altitude really do have more time, as do people who stay still. The difference as measured on an atomic clock is counted only in billionths of a second, and we on Earth can conveniently ignore this temporal untidiness. But everything in the universe is in motion; everything feels gravity’s grasp. Time shifts with both mass and velocity, to be different at every point in the universe: we live, Rovelli says, in a 'spiderweb of time'.