The order of time

Review by New York Times Review

THERE'S A PASSAGE in Carlo Rovelli's lovely new book, "The Order of Time" - a letter from Einstein to the family of his recently deceased friend Michele Besso: "Now he has departed from this strange world a little ahead of me. That means nothing... The distinction between past, present and future is only a stubbornly persistent illusion." Rovelli comments that Einstein was taking great poetic license with the temporal findings of his relativity theory, even to the point of error. But then the author goes on to say that the great physicist was addressing his letter not to scientists or philosophers, but to a bereft family. "It's a letter written to console a grieving sister," he writes. "A gentle letter, alluding to the spiritual bond between Michele and Albert." That sensitivity to the human condition is a constant presence in Rovelli's book - 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. The book is read by the British actor Benedict Cumberbatch, who has benefited from significant stage experience as well as starring in such films as "The Imitation Game" and the TV series "Sherlock." Cumberbatch possesses a deep and rich voice and reads the text in a precise but unhurried manner, with the result that we feel as if we are getting an exposition by an erudite but gentle teacher. The ancient Babylonians saw time as a wheel, repeating in cycles. Confucius likened the passage of time to the flow of a river's stream. For the kabbalists, time is an illusion. Isaac Newton conceived of time as a rigid scaffolding erected by God. Rovelli, who is a theoretical physicist at Aix-Marseille University in France and the author of the international best seller "Seven Brief Lessons on Physics," explains how scientists in his field look at time, seasoning his book with quotes from the likes of Horace and Shakespeare and a fair measure of his personal ruminations. His title was inspired by a fragment of the writings of the ancient Greek philosopher Anaximander (circa 600 B.C.): "Things are transformed one into another according to necessity, and render justice to one another according to the order of time." In response, Rovelli's book asks, Why should time have an order? And for whom? And to what end? Prior to Einstein, it was believed that time was absolute. A second was a second was a second, period. Time flowed in lock-step uniformity everywhere throughout the universe. The idea was so obvious as not to be questioned - until it was. In 1905, at age 26, Einstein first set out to explain the workings of electricity and magnetism. In the process, he proposed that identical clocks in motion relative to each other do not tick at the same rate. That seemingly absurd proposition has been proved. Later, Einstein conjectured, with a highly mathematical theory called general relativity, that gravity also affects the rate of ticking of clocks: A clock in strong gravity ticks more slowly than one in weak gravity. That claim has also been proved. The final insult: Two events that are simultaneous to one person are not for another person who is in motion with respect to the first. Thus the entire concept of "now" needs rethinking. Chapter by chapter, Rovelli shows how modern physics has annihilated common understandings of time. And both the writing and vocal delivery are beautiful. "Time is not a line with two equal directions: It is an arrow with different extremities. And it is this, rather than the speed of its passing, that matters most to us about time. This is the fundamental thing about time. The secret of time lies in this slippage that we feel on our pulse, viscerally, in the enigma of memory, in anxiety about the future. This is what it means to think about time. What exactly is this flowing? Where is it nestled in the grammar of the world?" Here Rovelli is raising yet another of time's mysteries. Why does it have such a clear directionality, with the future so easily distinguished from the past? Let me explain. If you see a film of a teapot first sitting on the edge of a table, then falling off the table and shattering into a thousand shards, the film appears perfectly normal. Evidently, someone jostled the table. But, if you were to watch a film in which shards of pottery scattered about on the floor suddenly rushed together and formed a teapot, which then jumped up to land on a table, you would interpret that film as being played backward in time. Because you've never seen such a sequence of events in the real world. Why not? The answer is a matter of probability. A broken teapot could indeed re-form itself from vibrations and heat in the floor, but it is highly unlikely. Physics shows that moving from order to disorder is more probable than the reverse - much more probable when it comes to large collections of atoms such as constitute a teapot. In scientific terms, this movement determines the direction of time. And the fact that this direction is so definite in all that we see, both on earth and beyond, means that the cosmos must have begun in a state of relatively high order - with plenty of room to make a mess in the future. It is that room for increasing chaos that drives the evolution of the universe, that drives change. Without it, stars and planets would never form, humans and other life-forms would never exist, and teapots would never be made in the first place, broken or otherwise. Physicists still do not understand why our universe appears to have been created with such a high degree of order. Rovelli suggests that it's a matter of our human "perspective," and depends on our "interactions" with the physical world. I respectfully disagree. It is theoretically possible for the universe to have been created in a state of nearly maximum disorder, in which case no evolution or change would occur. That would not be a matter of perspective. One possibility, entertained by a number of leading physicists, is that there are lots of universes, the so-called multiverse, with very different properties and initial conditions. Some of those universes may have started in conditions of maximum disorder, with nothing driving change, no distinction between future and past, where atom-size pottery shards gather themselves up to form atom-size teapots as often as the reverse. But some of these universes would have been created, by accident, with relatively high order. We live in such a universe because otherwise we wouldn't be here to discuss the matter. The theory of "quantum gravity," which is still not fully formulated, describes such a continuous creation of universes with random properties and initial conditions. Some elements of Rovelli's narrative, like the material on light cones and loop quantum gravity and spin networks, many readers will find incomprehensible. But the many other excellent explanations of science, the heart and humanity of the book, its poetry and its gentle tone raise it to the level and style of such great scientist-writers as Lewis Thomas and Rachel Carson. Listening to Rovelli's book, as read by Cumberbatch, we hear the warm voice of a modest man searching to understand not only the physical world but also how he, and we, perceive it. "Time, then, is the form in which we beings whose brains are made up essentially of memory and foresight interact with the world," Rovelli writes near the end. "It is the source of our identity." We hear the warm voice of a modest man searching to understand not only the physical world but also how he, and we, perceive it.

Copyright (c) The New York Times Company [May 20, 2018]

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Review by Booklist Review

*Starred Review* The hours readers spend with Rovelli will forever transform their understanding of time. With the help of adept translators, this acclaimed Italian physicist invites readers to join him in first deconstructing, then abolishing, and finally redefining the mystery we call time. Readers learn how even when we move past Aristotle and Newton by understanding time in terms of Einstein's conception of space-time, our temporal thinking obscures scientific realities. Indeed, the t of time in Einstein's formula simply breaks down in the granularity required by quantum mechanics. As Rovelli ushers astonished readers into the quantum wonderland, they contemplate loop-theory equations that deny time any relevance as a variable for explaining the universe. From that vantage point, readers realize that we can describe the happenings and relationships that make up our world without temporal terms. We persist in interpreting our world in such terms, Rovelli believes, not because of the nature of the universe but rather because of our nature as human observers and participants in that universe. Time has emerged as a distinctly human creation, forged in memory, shaped by grammar, poetry, religion, and music a creation less useful in science than scientists have long supposed but one still essential in exploring our subjective identity. A profound intellectual inquiry.--Christensen, Bryce Copyright 2018 Booklist

From Booklist, Copyright (c) American Library Association. Used with permission.

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Review by Publisher's Weekly Review

In this far-reaching text rife with references to poets, artists, and philosophers, as well as scientists, theoretical physicist Rovelli (Seven Brief Lessons on Physics) takes readers through the current scientific understanding of time, stating that "we inhabit time as fish live in water." Rovelli begins with a look at why time, Rainer Maria Rilke's "eternal current," only flows forward. Humans can see the past but not the future, he writes, because of how heat flows, from hot to cold. He states that "only where there is heat is there a distinction between past and future," using as an example a film of a rolling ball gradually slowing, due to heat-producing friction; if run backwards, the film becomes absurd. Entropy, "the quantity that measures this irreversible progress of heat in only one direction," provides the direction of "time's arrow." Meanwhile, the human perception of simultaneity, the idea of "now" in two different locations, is an illusion, an insight that Rovelli calls "perhaps the greatest and strangest of Einstein's discoveries." In considering time, Rovelli also explores quantum time, loop theory, and the nature of memory. As much philosophy as physics, this accessible study introduces the complex questions behind the perception and study of time. (May) © Copyright PWxyz, LLC. All rights reserved.

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Review by Library Journal Review

Rovelli (theoretical physics, Aix-Marseille Univ., France) is well known for his popular Seven Brief Lessons on Physics. This latest work offers a readable discussion of the unreality of time, especially if it is decoupled from space and heat, that unfolds chronologically, from Aristotle to Albert Einstein to the author's own discoveries and those of other contemporary quantum researchers. While appropriate for graduate level philosophy of science students, this volume is made more accessible by Rovelli's conversational writing style and approach, which incorporates allusions to music and art. The inclusion of diagrams, some whimsical (like an ancient family tree), are useful analogies for the complex concepts discussed. VERDICT An engaging and accessible exploration of our understanding of the nature of space time that should appeal to high school and adult readers interested in physics, epistemology, and perception.-Sara R. Tompson, Jet Propulsion Laboratory Lib., Archives & Records Section, Pasadena, CA © Copyright 2018. Library Journals LLC, a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.

(c) Copyright Library Journals LLC, a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.

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Review by Kirkus Book Review

Undeterred by a subject difficult to pin down, Italian theoretical physicist Rovelli (Reality Is Not What It Seems: The Journey to Quantum Gravity, 2017, etc.) explains his thoughts on time.Other scientists have written primers on the concept of time for a general audience, but Rovelli, who also wrote the bestseller Seven Brief Lessons on Physics, adds his personal musings, which are astute and rewarding but do not make for an easy read. "We conventionally think of time," he writes, "as something simple and fundamental that flows uniformly, independently from everything else, uniformly from the past to the future, measured by clocks and watches. In the course of time, the events of the universe succeed each other in an orderly way: pasts, presents, futures. The past is fixed, the future open.And yet all of this has turned out to be false." Rovelli returns again and again to the ideas of three legendary men. Aristotle wrote that things change continually. What we call "time" is the measurement of that change. If nothing changed, time would not exist. Newton disagreed. While admitting the existence of a time that measures events, he insisted that there is an absolute "true time" that passes relentlessly. If the universe froze, time would roll on. To laymen, this may seem like common sense, but most philosophers are not convinced. Einstein asserted that both are right. Aristotle correctly explained that time flows in relation to something else. Educated laymen know that clocks register different times when they move or experience gravity. Newton's absolute exists, but as a special case in Einstein's curved space-time. 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. Copyright Kirkus Reviews, used with permission.

Copyright (c) Kirkus Reviews, used with permission.

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Introduction: Perhaps Time is the Greatest Mystery I stop and do nothing. Nothing Happens. I am thinking about nothing. I listen to the passing of time. This is time, familiar and intimate. We are taken by it. The rush of seconds, hours, years that hurls us toward life then drags us toward nothingness.... We inhabit time as fish live in water. Our being is being in time. Its solemn music nurtures us, opens the world to us, trou­bles us, frightens and lulls us. The universe unfolds into the future, dragged by time, and exists according to the order of time. In Hindu mythology, the river of the cosmos is portrayed with the sacred image of Shiva dancing: his dance supports the coursing of the universe; it is itself the f lowing of time. What could be more universal and obvious than this flowing ? And yet things are somewhat more complicated than this. Reality is often very different from what it seems. The Earth appears to be flat but is in fact spherical. The sun seems to revolve in the sky when it is really we who are spinning. Neither is the structure of time what it seems to be: it is different from this uniform, universal flowing. I discovered this, to my utter astonishment, in the physics books I read as a university student: time works quite differently from the way it seems to. In those same books I also discovered that we still don't know how time actually works. The nature of time is perhaps the greatest remaining mystery. Curious threads connect it to those other great open mysteries: the nature of mind, the origin of the universe, the fate of black holes, the very functioning of life on Earth. Something essential continues to draw us back to the nature of time. Wonder is the source of our desire for knowledge, and the discovery that time is not what we thought it was opens up a thousand questions. The nature of time has been at the center of my life's work in theoretical physics. In the following pages, I give an account of what we have understood about time and the paths that are being followed in our search to understand it better, as well as an account of what we have yet to understand and what it seems to me that we are just beginning to glimpse. Why do we remember the past and not the future? Do we exist in time, or does time exist in us? What does it really mean to say that time "passes"? What ties time to our nature as persons, to our subjectivity? What am I listening to when I listen to the passing of time? This book is divided into three unequal parts. In the first, I summarize what modern physics has understood about time. It is like holding a snowflake in your hands: gradually, as you study it, it melts between your fingers and vanishes. We conventionally think of time as something simple and fundamental that f lows uniformly, independently from everything else, from the past to the future, measured by clocks and watches. In the course of time, the events of the universe succeed each other in an orderly way: pasts, presents, futures. The past is fixed, the future open. . . . And yet all of this has turned out to be false. One after another, the characteristic features of time have proved to be approximations, mistakes determined by our perspective, just like the flatness of the Earth or the revolving of the sun. The growth of our knowledge has led to a slow disintegration of our notion of time. What we call "time" is a complex collection of structures, of layers. Under increasing scrutiny, in ever greater depth, time has lost layers one after another, piece by piece. The first part of this book gives an account of this crumbling of time. The second part describes what we have been left with: an empty, windswept landscape almost devoid of all trace of temporality. A strange, alien world that is nevertheless still the one to which we belong. It is like arriving in the high mountains, where there is nothing but snow, rocks, and sky. Or like it must have been for Armstrong and Aldrin when venturing onto the motionless sand of the moon. A world stripped to its essence, glittering with an arid and troubling beauty. The physics on which I work--quantum gravity--is an attempt to understand and lend coherent meaning to this extreme and beautiful landscape. To the world without time. The third part of the book is the most difficult, but also the most vital and the one that most closely involves us. In a world without time, there must still be something that gives rise to the time that we are accustomed to, with its order, with its past that is different from the future, with its smooth f lowing. Somehow, our time must emerge around us, at least for us and at our scale. This is the return journey, back toward the time lost in the first part of the book when pursuing the elementary grammar of the world. As in a crime novel, we are now going in search of a guilty party: the culprit who has created time. One by one, we discover the constituent parts of the time that is familiar to us--not, now, as elementary structures of reality, but rather as useful approximations for the clumsy and bungling mortal creatures we are: aspects of our perspective, and aspects, too, perhaps, that are decisive in determining what we are. Because the mystery of time is ultimately, perhaps, more about ourselves than about the cosmos. Perhaps, as in the first and greatest of all detective novels, Sophocles' Oedipus Rex , the culprit turns out to be the detective. Here, the book becomes a fiery magma of ideas, sometimes illuminating, sometimes confusing. If you decide to follow me, I will take you to where I believe our knowledge of time has reached: up to the brink of that vast nocturnal and star-studded ocean of all that we still don't know. Excerpted from The Order of Time by Carlo Rovelli All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.

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