The Demon in the Machine: Paul Davies's Bid to Solve the Mystery of Life

Some books set out to answer a question, and some settle for asking it better. "The Demon in the Machine" (Allen Lane, 2019), by physicist Paul Davies, belongs unmistakably to the second category, and that turns out to be both its greatest virtue and its most obvious limitation. Under a title that promises an almost gothic revelation, and a subtitle — "How Hidden Webs of Information Are Solving the Mystery of Life" — that edges toward publishing hyperbole, Davies delivers two hundred and fifty pages of genuine erudition, lucid prose and, ultimately, more questions than certainties. That is not a minor flaw. It is, rather, the book's very condition.

Davies is no newcomer to these waters. A professor at Arizona State University and director of the Beyond Center for Fundamental Concepts in Science, winner of the 1995 Templeton Prize and author of more than twenty books — including "The Mind of God," "About Time" and "The Goldilocks Enigma" — he has built an entire career on the uncomfortable border where theoretical physics brushes against metaphysics without quite falling into it. That reputation as an elegant translator of difficult ideas precedes the book and, to a large extent, carries it: whenever the argument grows slippery, it is the author's clear, confident voice that keeps the reader on board.

The book also arrives at an opportune moment in a long and singular career. Davies chairs the SETI post-detection task group — the body that would spring into action should a signal of extraterrestrial intelligence ever be confirmed — and an asteroid, 1992OG, was named after him in recognition of his work in science communication. That profile of scientist-philosopher, equally at home in mathematical rigor and wide-ranging speculation, explains why "The Demon in the Machine" can leap unashamedly from statistical thermodynamics to the question of the origin of consciousness without the reader feeling, at least not immediately, that the ground has turned to quicksand.

The project is ambitious to the point of recklessness. Davies wants to unify molecular biology, information theory, thermodynamics, quantum chemistry and nanotechnology under a single question that, despite having been posed for nearly a century, still lacks a satisfying answer: what is life? The book takes as its explicit starting point Erwin Schrödinger's eponymous 1944 essay, which already warned that the very existence of living organisms seems to defy the second law of thermodynamics — the law that condemns every closed system to entropy and disorder. Eighty years on, Davies argues, we still lack a convincing physical explanation for how life manages, seemingly as a matter of routine, to build order out of chaos.

The book's title refers to Maxwell's famous thought experiment: a tiny "demon" capable of sorting fast molecules from slow ones and thereby, in theory, violating the second law without any apparent expenditure of energy. Davies traces the history of that idea — from its nineteenth-century absurdity to the "molecular motors" now genuinely built in nanotechnology labs — to argue that living cells function, in essence, as Maxwell's demons perfected by evolution: information-processing machines that manage to maintain biological order while paying, without complaint, the energetic price thermodynamics demands.

It is in this first stretch that the book is at its best. Davies writes with the ease of someone who has spent decades explaining complex ideas to non-specialist audiences, and he manages to make concepts such as Shannon entropy, Brownian motors, and the causal power of information — the idea, dear to the author, that information is not a mere epiphenomenon but an entity with its own causal power over matter — not merely comprehensible but genuinely gripping. The philosophical ambition is clear: Davies wants to dethrone matter as physics's sole protagonist and seat information beside it on the throne. It is a thesis with lineage — it owes something to Wheeler and his "it from bit" — but Davies presents it with freshness and takes it into biological territory where it had rarely been pursued in this much detail.

The book's second half, devoted to quantum biology, is more uneven. Davies surveys the evidence — still partial, and in many cases disputed within the scientific community itself — that quantum phenomena such as entanglement or tunneling might play a role in specific biological processes: the near-perfect efficiency of photosynthesis, the remarkable ability of certain migratory birds to orient themselves via a supposed "quantum compass" in their retinas, or the mechanism by which enzymes speed up chemical reactions through proton tunneling. These are fascinating subjects, and Davies narrates them with the enthusiasm of a tour guide who knows the terrain, but the attentive reader will notice that much of this section rests on preliminary research, results that are not always replicated, and a careful cascade of conditionals. Davies himself is honest about this — he is careful to distinguish the established from the speculative — but that honesty does not dissolve the sense that the book keeps promising a synthesis it postpones, chapter after chapter.

That is the main objection to be raised against "The Demon in the Machine": the distance between what the subtitle announces and what the content ultimately delivers. Specialist reviews have rightly noted that the book offers a series of speculative and at times meandering chapters, some genuinely hard going for the non-expert reader, rather than the grand unifying synthesis the cover suggests. And there are passages — such as the chapter on the origins of cancer, where Davies allows himself to speculate about an "evolutionary reversion" of cancer cells toward primitive unicellular states — in which rigor gives way to personal conjecture, without the empirical backing the rest of the book does try to provide. It is the moment when the essayist overtakes the scientist, and not always for the better.

In fairness, it should be said that this tension between rigor and speculation is not a stylistic accident but the very nature of the territory Davies has chosen to map. He is exploring, in his own words, a field so new it does not yet even have a name: the intersection of biology, computing, logic, chemistry, quantum physics and nanotechnology. Writing about an active research frontier — where specialists themselves disagree — forces any honest popularizer to walk on thin ice. Davies does so more carefully than most, explicitly flagging when he leaves the solid ground of the demonstrated for the realm of hypothesis. But the reader who arrives looking for closed answers — the "mystery solved" the title promises — will come away disappointed, and that disappointment, however predictable, is nonetheless legitimate.

The book was named Book of the Year 2019 by Physics World, an honor its editors justified by calling it a demanding but immensely captivating, rewarding and enjoyable read. That is a fair verdict. Davies is not a popularizer who dumbs down difficult subjects to win over an audience; on the contrary, he demands from the reader sustained attention and a reasonable tolerance for ambiguity. In exchange, he offers some of the most elegant prose to be found today in English-language science writing, capable of explaining in a single page what other authors would need an entire chapter to muddle through.

It is worth situating the book within the tradition it belongs to: that of physicists who, at a certain stage in their careers, allow themselves to speculate about biology and consciousness with the same freedom they once reserved for black holes or quantum cosmology. Schrödinger inaugurated the genre in 1944; Davies continues it with the advantage of eight additional decades of molecular biology, but also with the risk run by any physicist venturing into unfamiliar biological terrain: that of underestimating the historical, contingent complexity of living systems in favor of elegant, universal physical laws. Some biologists have raised precisely that objection — that Davies, dazzled by the mathematical elegance of information and thermodynamics, tends to underplay how much of biology is simply the accumulated, messy, inelegant result of billions of years of trial-and-error evolution. It is a criticism the book never fully disarms, though it does not entirely ignore it either.

That same risk — the physicist crossing a disciplinary border armed with formulas but a shallower grasp of evolutionary biology — has predictably produced polarized reactions among specialists. While outlets such as Physics World celebrated the book for its ambition and clarity, other reviewers from the biological sciences have been less forgiving, arguing that certain chapters lean toward uninformed speculation rather than rigorous synthesis. This split should surprise no one familiar with the genre: books bold enough to cross disciplinary lines rarely satisfy the gatekeepers of every discipline equally, and "The Demon in the Machine" is no exception. What sets Davies apart from less scrupulous popularizers is that he himself seems aware he is treading on someone else's ground, and he flags it with an honesty that tempers, without entirely eliminating, the risk of overreach.

It is also worth noting the publishing moment in which the book appears. Originally published by Allen Lane in January 2019 and reissued shortly afterward by University of Chicago Press, "The Demon in the Machine" joins a recent wave of titles attempting to bridge the physics of information with the life sciences — a field that, as Davies himself acknowledges, still lacks a proper name but is already generating its own specialized literature, including an academic anthology co-edited by Davies himself alongside Sara Imari Walker and George Ellis for readers wanting to go beyond the popular format. That editorial context is worth bearing in mind: this is not an isolated curiosity but a symptom of where much of contemporary theoretical physics is heading once it finally turns its gaze toward biology.

Who should read this book? Any reader willing to trade certainties for better-framed questions. Anyone seeking a rigorous — if demanding — introduction to why life seems, from a thermodynamic standpoint, almost a statistical miracle, and to science's most recent attempts to explain that miracle without resorting to metaphysics. It is not, on the other hand, a book for those seeking definitive answers wrapped in agreeable prose; such a reader will run into the same unspoken but omnipresent refrain, chapter after chapter: "we still don't know this for certain."

And perhaps that, after all, is the book's most honest contribution. In a genre — popular science writing about the "great mysteries" — crowded with promises of final synthesis and definitive answers, Davies chooses the less flashy but more honorable path: showing precisely where the edge of our current knowledge lies, without pretending to have crossed it. "The Demon in the Machine" does not solve the mystery of life. But it leaves the reader better equipped to understand why that mystery remains, quite rightly, unsolved — and why the answer, when it comes, will likely owe as much to biology as to physics, and no small part to the information flowing, invisibly, between the two.

Closing the book, one is left with the sense of having been guided by a brilliant companion through territory still not fully mapped. Davies does not pretend to know the whole route, and that intellectual modesty — rare in a genre so given to grandiosity — is perhaps the true achievement of "The Demon in the Machine": not solving the riddle of life, but finally posing it with the precision it deserves.

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