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A quantum physicist reveals why time is not as simple as it seems

The Order of Time

Carlo Rovelli
Riverhead Books
2018
250 pp.
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Carlo Rovelli, best-selling author of Seven Brief Lessons on Physics, is back with a new book, The Order of Time. This latest venture offers insight into the notion of time, including narratives on how our understanding of the concept has changed from antiquity to the present, as well as a concise update on how time is understood today through the lens of quantum mechanics.

Ordered into three parts in which Rovelli, a theoretical physicist and philosopher, gradually deconstructs and rebuilds our picture of time, the book is a nice follow-up to his last title, Reality Is Not What It Seems. In that book, the author briefly explored what his work on quantum gravity implies about the concept of time but left the topic open for further thought.

This book leads on by tackling some of the most fundamental questions one could ask about the nature of the universe: “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’?”

From Aristotle and Newton to Einstein, who first made the connection between space-time and the gravitational field, Rovelli explains that there can be no clear concept of the present everywhere in the universe. “There is no special moment on Proxima b that corresponds to what constitutes the present here and now,” he writes. “In my opinion, [this] is the most astounding conclusion arrived at in the whole of contemporary physics.”

In an interview with the author, conducted for this review, he summarized the take-home message of the book as follows: “Time is not a single notion; it is multifaceted, and to study it scientifically, we must disentangle it.” As a means of doing so, Rovelli takes readers on a journey into the field of quantum gravity, his own area of expertise. His ideas are both built on Einstein’s but also—because of the nature of quantum mechanics—somewhat in rejection of them.

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Einstein’s exposure to railway clock synchronization patents may have informed his later theories.

Rovelli maintains that our experience of time owes to a blurred, macroscopic perspective of the world that we encounter as human beings. “The distinction between past and future is tied to this blurring and would disappear if we were able to see the microscopic molecular activity of the world,” he argued during our interview. In other words, the past and the future are equally determinable at the molecular level.

In an interesting chapter entitled “The Inadequacy of Grammar,” Rovelli looks at how language has affected the way we think about time. “We say that an event ‘is,’ or ‘has been,’ or ‘will be,’” he writes. “We do not have a grammar adapted to say that an event ‘has been’ in relation to me but ‘is’ in relation to you.” Rejecting the notion of an “objective global present,” he argues that if grammar is too imprecise to describe reality, we must change it.

Rovelli also looks in detail at the nature of entropy, arguing that it, too, is multifaceted and should be considered relativistically. “The entropy of the world does not depend only on the configuration of the world,” he writes in a chapter entitled “Perspective.” “[I]t also depends on the way in which we are blurring the world, and this depends on what the variables of the world are that we interact with.”

Where other writers struggle to get their complex ideas across, Rovelli introduces profound notions with ease, using simple but evocative language. “The absence of time does not mean … that everything is frozen and unmoving,” he writes, for example, in chapter 6. “It means that the incessant happening that wearies the world is not ordered along a time line, is not measured by a gigantic ticktocking.”

He also has a knack for mixing his serious enterprise with a sense of humor. “The events of the world do not form an orderly queue, like the English,” he writes. “They crowd around chaotically, like Italians.”

Ultimately, Rovelli believes that the multifaceted nature of time will become a universally acknowledged truth and that our current conceptions of time will be cast aside. “One after another,” he writes, “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.”

Like most astounding truths that have been revealed, these new ideas will likely be hard to accept at first, too.

About the author

The reviewer is a science journalist and founding editor of www.wideorbits.com. He can be found on Twitter at @ConorPPurcell.