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'.

...a book that reviews all of the best scientific thinking about the perennial mystery of time, from relativity to quantum physics to the inexorable second law of thermodynamics. Meanwhile, he always returns to us frail human beings — we who struggle to understand not only the external world of atoms and galaxies but also the internal world of our hearts and our minds.

According to theoretical physicist Carlo Rovelli, time is an illusion: our naive perception of its flow doesn’t correspond to physical reality. Indeed, as Rovelli argues in The Order of Time, much more is illusory, including Isaac Newton’s picture of a universally ticking clock. Even Albert Einstein’s relativistic space-time — an elastic manifold that contorts so that local times differ depending on one’s relative speed or proximity to a mass — is just an effective simplification ...The Order of Time is a compact and elegant book...raising and explore big issues that are very much alive in modern physics, and are closely related to the way in which we limited beings observe and participate in the world.

No one writes about the cosmos like theoretical physicist Carlo Rovelli. He may not be as well known in the United States as the late Stephen Hawking, Neil deGrasse Tyson or Alan Lightman...but in The Order of Time, he shares his enthusiasm as he discusses scientifically and philosophically the 'greatest remaining mystery': the nature of time ... Some of Rovelli’s critics, like physicist Lisa Randall, who also quotes Rilke, have accused Rovelli of romanticism, but I find an elegant grandeur in how he relates the worlds of science, philosophy and art. ... Who can resist reading a physicist who writes, 'We can go back to serenely immersing ourselves in time — in our finite time — to savoring the clear intensity of every fleeting and cherished moment of the brief circle of our existence'?

Undeterred by a subject difficult to pin down, Italian theoretical physicist Rovelli explains his thoughts on time. Other scientists have written primers on the concept of time for a general audience, but Rovelli...adds his personal musings, which are astute and rewarding but do not make for an easy read. According to Rovelli, our notion of time dissolves as our knowledge grows; complex features swell and then retreat and perhaps vanish entirely. Furthermore, equations describing many fundamental physical phenomena don’t require time. As much a work of philosophy as of physics and full of insights for readers willing to work hard.