Reality Is Not What It Seems: The Journey to Quantum Gravity, by Carlo Rovelli, Allen Lane, 256 pp, £16.99, ISBN: 978-0241257968
Carlo Rovelli was on a nighttime journey from Italy to France when an insight came to him that caused him to drive too fast: he could best explain how the world is seen when quantum physics is applied to gravity by telling the story of how this understanding developed. The resulting book is, he says, “a travel book that describes one of the most spectacular journeys that humanity has taken”.
Rovelli proposes this book as a “work of divulgation”. And well you might pause – divulgation? This is the literal English equivalent of divulgazione, for which there is a well-recognised substantive equivalent: popularisation ‑ a curious lapse in a translation that otherwise reads well.
Reality can take its place in the burgeoning popular science sections of bookshops. (A Dublin shop displayed some new titles of this genre at Christmas, with a poster: “Science! The New Religion”.) Rovelli has already ridden the wave of this publishing phenomenon, having extraordinary success with his Seven Brief Lessons on Physics (2015). He paused work on Reality Is Not What It Seems to respond to his Italian publisher’s request for that more basic book; it sold over 300,000 copies in Italy and has been published in over forty languages, thoroughly vindicating the publisher’s wager.
Reality covers some of the same ground as Seven Brief Lessons, but it does so with stronger focus on the formal detail of quantum physics, its recent directions and its current challenges. It uses some of the didactic approach of Seven Brief Lessons, usefully updating his answer to the question “What is the world made of?” to take account of the historical advances he reports. But it also takes a very broad historical sweep and offers something to history and philosophy of science as well as to the popularisation of physics. In these respects and in its frequent presentation of complex formulae and equations, including unexplained mathematical symbols, Reality is both more and less than popular science as we generally know it.
There have been many other works that present quantum theory in various popularising forms. Just taking examples from my own shelves, these include: Quantum Theory – a Graphic Guide to Science’s Most Puzzling Discovery (1997), a Guardian publication reprinted eleven times in the decade after its first publication; a short profile, Bohr and Quantum Theory (1998), by Trinity College Dublin graduate Paul Strathern in the Big Idea series of popular science books; Chad Orzel’s manual, How to Teach Quantum Physics to Your Dog (2010), reprinted every year since its first publication; a brilliant biography, The Strangest Man – the Hidden Life of Paul Dirac, Quantum Genius (2009), by science historian and communication consultant Graham Farmelo.
Reality begins its journey in Greece 2,600 years ago, with scholars whose work has only partially survived. Democritus produced many works which are known only through their listing and reporting by others. But even in the absence of originals, Rovelli confidently claims Democritus’s work as a direct ancestor of quantum physics for his insight that all matter is comprised of atoms. He continues his story of science as a history of ideas that links Democritus, Newton, Faraday and Planck across the cultures and the centuries. There are details of experiments and proofs and, as the story comes to the late twentieth and early twenty-first centuries, some mind-bogglingly difficult concepts and formulae accessible only to a few.
Rovelli addresses us directly as “Dear Reader”, coaxing us through the denser passages, but also seeking to persuade us of the validity of his particular version of quantum theory. He is an advocate for the notion of all matter being in the form of loops (of quanta). On the basis that a credible theory should be capable of being presented on a T-shirt, he offers us an image of a shirt with the equations that summarise loop quantum gravity. Booksellers might consider presenting a free copy of the book to anyone who can offer a plausible explanation of even one of these three equations which Rovelli cautions “may not be correct”.
There are approaches apart from loop theory, notably string theory, which also has a well-established populariser, Brian Greene, on its side. Rovelli presents validation for his view by reference to three scholars who have published analyses of it. They are philosophers, for in theoretical physics the elegance and coherence of the argument matter at least as much as the experimental verification of the ideas. Indeed, experimental proofs may not (yet) be available for much of what is presented here.
Not surprisingly then, Rovelli has a strong interest in the limits of scientific knowledge. An important part of his invitation to his “Dear Reader” is to understand the uncertainty of science. He shows awareness of the insights of sociology of science, which deals with the contingency of its processes and products. He closes with a philosophical exploration of ignorance and a questioning of the notion of Truth (with a capital T). In all of this, Reality is especially stimulating and again deviant within popular science. More typically, works in this genre seek to make accessible the certain or near-certain acquisitions of knowledge through science.
On the first page of his preface, he introduces the crucial paradox that “the more we discover, the more we understand that what we don’t know is greater than what we know”, and he returns to this theme in the short closing chapter, “Mystery”. Along the way, he states that “it is characteristic of genius to be aware of the limitations of its own findings”, and reminds us that Richard Feynman, a major contributor to quantum theory, famously said: “I think I can state that nobody really understands quantum mechanics.”
Rovelli deploys many of the devices of the popular science genre, for example, making extensive use of metaphor and analogy in explaining the shifting ideas and representations of the basic building blocks of matter, including space. In the discussion of lines, waves and fields, he returns repeatedly to the notion of weaving, as in: “Faraday’s lines of the quantum gravitational field are the threads of which space is woven.” Those threads are also the loops of Rovelli’s version of quantum gravity theory. From Einstein he borrows a different image of space as a mollusc, in Rovelli’s words, “an immense, mobile mollusc”.
He has telling anecdotes and biographical detail about the historical figures he meets on the journey, including the Belgian priest-physicist Georges Lemaître who argued with Pope Pius XII, the Austrian Ludwig Boltzmann who was “not taken seriously”, committed suicide in 1906 and has his formula carved on his tombstone, and the Soviet scientist Matvei Bronstein, who made an important contribution to the quantum endeavour aged thirty and was executed two years later in February 1938 in Stalin’s Leningrad prison.
Rovelli seeks to enthuse us by referring to discoveries and ideas as “fascinating”, “strange”, “remarkable” and – three times in six pages – “beautiful”. His enthusiasm perhaps gets the better of him when he asks towards the end of the book, “What is the world made of? The answer now is simple.” So, here, Dear Reader of this review, is that simple answer: “The particles are quanta of quantum fields; light is formed by quanta of a field; space is nothing more than a field, which is also made of quanta; and time emerges from the processes of this same field. In other words, the world is made entirely from quantum fields.”
Again becoming somewhat overexcited, Rovelli claims that the detection of gravitational waves produced by two black holes falling into one another and reported in early 2016 “left the world speechless”. In fact, the scientific world spoke about it a great deal and a mathematical physicist whom I asked for his highlight of 2016 barely paused before nominating this announcement. Mass media across the world reported it as confirmation of a key piece of Einstein’s theory of general relativity.
Among the many digressions Rovelli uses to make the arcane science more culturally meaningful is an extended and repetitive treatment of Dante’s representation of the universe in the Commedia as prefiguring understandings developed by physicists seven centuries later. The publisher of Reality has indulged Rovelli with this and many other illustrations, including small “mug-shots” of the physicists contributing to the story that provide some visual relief but don’t add significantly to the substance of the case being made. Colour, we are told, is an important distinguishing characteristic of all matter and to illustrate this Reality contains an image of “the spectra of some elements: sodium, mercury, lithium and hydrogen”; it is in black and white and quite meaningless.
In the style of more formal scientific writing, there are many footnotes, often with equations, diagrams or formulae that, presumably, deepen the discussion for those who can read them. But he loses sight of his intended reader, “someone who knows little or nothing about today’s physics but is curious to find out what we know” when he introduces as “simple” a footnote that runs to more than a page. This presents an equation which, even with definitions provided of all the symbols and a table of values, could hardly be considered simple.
The stages of Rovelli’s journey differ in length and style, perhaps reflecting the time out taken to write Seven Brief Lessons, but he swings along compellingly in parts and the journey does bring its rewards. Having read it you may not be able to tell your friend over a coffee how this quantum world works but you can always fall back on Feynman. Maybe nobody really understands.
Brian Trench is a science communication researcher and trainer, formerly senior lecturer at Dublin City University. He is president of the international PCST (Public Communication of Science and Technology) network and co-editor of the Routledge Handbook of Public Communication of Science and Technology (2008 and 2014).