The Or­der of Time

The Week (US) - - 22 - By Carlo Rovelli

(River­head, $20) Carlo Rovelli’s new book on the na­ture of time de­serves to be­come a con­tem­po­rary clas­sic, said Philip Ball in New Sci­en­tist. As he demon­strated in Seven Brief Les­sons on Physics, the Ital­ian the­o­ret­i­cal physi­cist is a re­mark­ably ef­fec­tive writer—“po­etic with­out be­ing twee, learned with­out os­ten­ta­tion, au­thor­i­ta­tive yet con­ver­sa­tional.” Here, in fewer than 250 pages, he el­e­gantly ex­plains how physi­cists’ un­der­stand­ing of time has changed, more than once, since Isaac Newton’s day. Ex­perts won’t come across any ideas they haven’t en­coun­tered be­fore. And yet noth­ing in The Or­der of Time reads like mere review, be­cause Rovelli il­lu­mi­nates each con­cept us­ing novel metaphors and per­spec­tives. “Bet­ter still, he reaches into the heart of the mat­ter in ways that make you think afresh.”

To Rovelli and his peers, time is an illusion, said Andrew Jaffe in Na­ture. Though we in­tuit, as Newton did, that time passes at a sin­gle rate through­out the cos­mos, ev­i­dence has proven its pace varies de­pend­ing on the ob­server’s speed and lo­ca­tion, just as Ein­stein the­o­rized. Rovelli ar­gues that this sug­gests that time ex­ists only in per­cep­tion. “So what does he think is re­ally go­ing on?” He pro­poses that re­al­ity is a com­plex net­work of events gov­erned by the laws of physics, onto which we sub­jec­tively project se­quences that we per­ceive as past, present, and fu­ture. “Ul­ti­mately, I’m not sure I buy Rovelli’s ideas”; to ac­cept ev­ery­thing he says, we would have to em­brace loop quan­tum the­ory, an al­ter­na­tive to string the­ory that is Rovelli’s “am­bi­tious” bid to wed quan­tum me­chan­ics and rel­a­tiv­ity the­ory. Lu­cid as its ex­pla­na­tions are, “this book alone would not give the lay reader enough in­for­ma­tion to ren­der a judg­ment.”

Many of the strange paths Rovelli leads us down aren’t new, said Tim Rad­ford in The­Guardian.com. “Aris­to­tle and St. Au­gus­tine both wres­tled with the pro­tean ques­tion of time,” and Rovelli is con­ver­sant enough with the work of artists and philoso­phers that he’s able to grace­fully weave their voices into the con­ver­sa­tion, a con­ver­sa­tion that in­evitably leads to the propo­si­tion that re­al­ity is not what it seems. The book is, in the end, “a joy to read.” Rovelli’s rea­son­ing isn’t al­ways easy to fol­low, “and when you close the book you still won’t know whether time re­ally ex­ists or not.” That’s OK: “You will have a sharper sense of why you don’t know.”

At a cos­mic level, does time even ex­ist?

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