- \n
- Cosmos<\/a><\/li>\n<\/ul>\n
29 May, 2018<\/p>\n
![\"\"](\"https:\/\/standpointmag.co.uk\/wp-content\/uploads\/2019\/03\/files_u28_Cosmos_rovelli.jpg\" "\\"Feature")
<\/p>\nIn his famous essay on the unfortunate distrust between science and the arts in British intellectual life, C. P. Snow wrote that he had often been at gatherings of \u201chighly educated\u201d people \u201cwho have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare\u2019s?\u201d<\/p>\n
Indeed, the second law of thermodynamics, that heat passes from warm things to cold things rather than the other way round, or more precisely that available energy always tends to become unavailable, is fundamental to our notion of time\u2019s arrow. By contrast, Newton\u2019s physical laws work equally forwards or backwards in time, so something has to distinguish one direction from the other and thermodynamics does this, giving what Carlo Rovelli in his new book (The Order of Time<\/em>, Allen Lane, \u00a312.99) calls \u201cthermal time\u201d. Yet he starts with subtleties that most of us never think about: time passes more quickly up a mountain than it does down in the plains. This is not a matter of perception but the simple fact that an atomic clock up a mountain will count more nanoseconds than one on the plain. The stronger the gravitational field the weaker the passage of time, until on the surface of a black hole there is none at all.<\/p>\n
This feature of Einstein\u2019s General Theory of Relativity is easier to grasp than the usual \u201cspace-twins paradox\u201d of special relativity where the twin who travels very fast out into space and back ages less than the one left at home. Nothing travels faster than a ray of light, for which time stands still, and Rovelli uses this to point out there is no such thing as a present time throughout the universe. There is a here and now, but the speed of light is not infinite and the concept of \u201cnow\u201d can only be a local one: \u201cOur present does not extend throughout the universe. It is like a bubble around us.\u201d If we measure time in nanoseconds the bubble extends only a few metres, if by milliseconds it extends over thousands of kilometres, and if we blur things to the nearest tenth of a second it extends over the whole planet. Blurring things avoids quantum phenomena, but time seems to vanish at the very tiniest scales and Rovelli phrases things in picturesque terms: \u201cThe events of the world do not form an orderly queue, like the English. They crowd around chaotically, like the Italians . . . [things] are happening; it is not stasis . . .\u00a0 The fundamental equations do not include a time variable, but they do include variables that change in relation to each other.\u201d
As well as dealing in a light-hearted way with some very serious physics, Rovelli (who works on quantum gravity), mixes in literary references showing that he at least straddles the cultural divisions that annoyed Snow. He quotes Horace, Shakespeare and others, but the longest quote is from Hugo von Hofmannsthal\u2019s wonderful libretto to Richard Strauss\u2019s Rosenkavalier. Yet the quotation is put together from three separate musings by the Marschallin: the first alone after Ochs has left and she recalls her younger life, the second in conversation with Octavian as she fears losing him, and the third from her soliloquy on the passing of time, Die Zeit die ist ein sonderbar\u2019 Ding<\/em> (Time is an extraordinary thing). But having reached this far into the book I already had my doubts about the presentation.<\/p>\nThe author starts very well with differences in the passage of time under different gravitational field strengths, or different states of motion, along with the direction of time\u2019s arrow that emerges from thermodynamics, but the quantum phenomena in chapters eight and nine are not well explained. \u201cThe theory [loop quantum gravity] describes how things change one in respect to the others, how things happen in the world one in relation to each other. That\u2019s all there is to it.\u201d Surely there must be more one can say, but in the end-note for this excerpt the author gives mathematical formulations without adequate explanation, basically saying: I know what I\u2019m talking about, but can\u2019t explain it to you \u2014 which is a case of talking down to the reader.<\/p>\n
Earlier when he is dealing with the light-cones of relativity theory, he alludes to the passing of a gravitational wave creating conditions where \u201cadvancing always towards the future, one can return to the same point in spacetime\u201d. This is time travel, as usually understood, but we need more context to the statement that \u201cthere is no logical contradiction entailed by the existence of closed temporal lines or journeys into the past; we are the ones who complicate things with our confused fantasies about the supposed freedom of the future\u201d. Rather than explain what he\u2019s getting at here he goes straight on to black holes: \u201cIt is the curious local structure of the present that produces black holes.\u201d Really? I thought it was gravity that produces black holes, and that as you approach them the \u201clocal structure\u201d (of space-time) breaks down.<\/p>\n
As a popular guide to the author\u2019s specialisation of quantum loop gravity this does not cut the mustard. It is more a poetic meditation on the passing of time, which ends with allusions to Augustine, the Vedas, and the Benedictus from Beethoven\u2019s Missa Solemnis<\/em>, rounding off with a quotation from Ecclesiastes: \u201cThe silver thread is broken, the gold lantern is shattered, the amphora at the fountain breaks, the bucket falls into the well, the earth returns to dust.\u201d He omits the next line, \u201cand the spirit shall return unto God who gave it\u201d, betraying a distrust of \u201ceternalism\u201d and disbelief in anything outside spacetime. He stays therefore very much in the realm of physics, but I would have loved more clarity on how quantum gravity creates the time from which the author finds his inspiration. Certainly Rovelli straddles the divide between science and the arts, but after a strong start the arguments dissipate about halfway through, and the book leaves scientific matters too vague. <\/p>\n
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