April 15, 2018
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.

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May 7, 2018
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 15, 2018

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

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Starred review from April 15, 2018
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.(Reprinted with permission of Booklist, copyright 2018, American Library Association.)