In 1944, the great Austrian physicist Erwin Schrödinger published one of the most influential science books of the 20th century, entitled What is Life? Based on a series of lectures delivered in Dublin, it showed how the principles of physics could help research in biology — and it inspired a postwar influx of physicists into the life sciences, who then played a key role in solving problems such as the mechanism of genetic inheritance.
Paul Davies, originally from London and currently a professor at Arizona State University, is not a scientific giant on the scale of Schrödinger (a father of quantum theory) but he has had a distinguished career in theoretical physics. His increasing interest in biology now manifests itself in a book that asks the same question as Schrödinger’s — and, he clearly hopes, will be similarly influential 75 years later.
While neither author can say what life is at the most fundamental level, both books look for an answer in future by bringing in expertise from another discipline. In Schrödinger’s case it was physics, in Davies’s it is information science. The flow of information through living organisms, he argues in The Demon in the Machine, is the missing ingredient that must be added to physics, chemistry and biology. In order to understand life, we must treat living creatures as computers and biological information as the software of life.
By information, Davies means far more than the data that we process in our brains and encode in our genes. He is talking broadly about information as a property or quantity of nature, like energy, which can directly bring about changes in physical and biological materials. The concept seems familiar and pragmatic but at the same time it is abstract and mathematical.
A weakness of The Demon in the Machine is that the book fails to explain clearly near the beginning quite what information means and doesn’t mean. It may be difficult to grasp in this unfamiliar scientific context but Davies, who is generally excellent at communicating complex ideas to non-experts, leaves the reader to work too hard at it.
In essence, information is what you know for certain about an object or system, for example its position or movement. It is the opposite of uncertainty or entropy, which is a scientific measure of disorder. Although information must be held within matter, Davies maintains — somewhat controversially — that at the same time we should think of its having an autonomous existence that can be passed from one physical system to another, rather like energy.
The book’s title comes from a thought experiment proposed in 1867 by the Scottish physicist James Clerk Maxwell. He imagined a box of gas divided into two chambers by a screen down the middle. A microscopic demon stands beside a small gate in the screen, watching the gas molecules moving randomly at slightly different speeds. When a fast molecule approaches the gate from the left chamber, Maxwell’s demon opens it and allows the molecule to pass into the right-hand chamber. Conversely, he lets slower molecules move into the left chamber.
Over time the right chamber becomes warmer than the left, because it holds the faster molecules, creating a heat gradient that could power an engine and therefore carry out useful work. For Maxwell and his contemporaries, the thought experiment was something of a paradox because it appeared to create order out of disorder and therefore to contravene the second law of thermodynamics, which holds that total entropy always increases in a closed system.
The paradox has recently been resolved, by taking account of information flow. The demon knows the speed and direction of incoming gas molecules. As the experiment proceeds, the erasure of this information from the demon’s memory fuels an “information engine” that converts the molecules’ motion into useful work.
Physicists are now moving Maxwell’s demons beyond thought experiments, constructing real nano-machines that extract energy from molecular motion. One example cited by Davies is a Japanese team that, by manipulating the thermal agitation of a polystyrene bead, turned information into energy with 28 per cent efficiency; the researchers envisage designing a future nano-engine that runs solely on “information fuel”.
But evolution has already filled living cells with information-fuelled nano-machines — proteins that act as miniature motors, pumps, shears, rotors, levers and ropes. One example is a freight delivery molecule called kinesin. It carries cargo such as cellular building blocks by walking along the microscopic fibres that criss-cross cells. Kinesin has a ratchet mechanism to propel it forward and prevent it being knocked back by the thermally agitated water molecules hitting it from all directions.
As Davies puts it, “organisms are replete with minuscule machines chuntering away like restless Maxwell demons, keeping life ticking over. They manipulate information in clever, super-efficient ways, conjuring order from chaos, deftly dodging the strictures of thermodynamics’ killjoy second law.” Evolution has refined biological information management machinery to operate with supreme efficiency, to prevent organisms cooking themselves to death with waste heat.
We know in broad terms how the machinery of life is passed on from one generation to the next, encoded as genes in DNA, in a way that transmits the inheritance almost perfectly while making the occasional mutations without which evolution could not take place. But much remains to be discovered about the way genes are switched on and off in different parts of the body at different stages of life and in response to different environmental stimuli — a field known as epigenetics.
In some 21st-century research, echoes are emerging of Jean-Baptiste Lamarck, the French naturalist who proposed at the beginning of the 19th century that an organism could transmit characteristics acquired during its lifetime to its offspring. Evidence that epigenetic information can be passed on between generations is growing. For instance the children of the women who were pregnant during the Dutch “hunger winter” famine of 1944-45 were born small; when they grew up and had children of their own, this third generation was also smaller than average.
The extent of epigenetic inheritance is scientifically controversial. Even more controversial is the idea that cells can rewrite their core genome, the DNA itself, because it contravenes the central dogma of Darwinian biology, as interpreted by modern genetics — that information flows one-way from inert DNA to proteins, the functional molecules of biochemistry. In computer terms, the Darwinian genome is a read-only file.
In reality it is more accurate to think of the genome as a read-write storage system, though as Davies points out, “orthodox biologists are not taking this assault lying down. The heresy of Lamarckism is always guaranteed to inflame passions.”
How the whole process started — the origin of life — remains a total mystery. The problem is doubly difficult because life is both hardware (chemistry) and software (information). Chemists have proposed various pathways that could have taken place on the young Earth, whether in Darwin’s famous “warm little pond” or in the hellish heat of subsea volcanic vents, or even somewhere extraterrestrial. But the emergence of a viable genetic code, robust enough to transmit information reliably to future generations and flexible enough for organisms to change over time, has no plausible explanation. “We remain almost completely in the dark about how life began, so attempts to estimate the odds of it happening are futile,” Davies writes. “You cannot determine the probability of an unknown process! We cannot put any level of confidence, none at all, on whether a search for life beyond Earth will prove successful.”
But, taking the optimistic view that life starts easily and is widespread in the cosmos, Davies renews a plea that he has made previously for funding to look for a “shadow biosphere” here on Earth, a search that has not yet been undertaken on a serious scale. He argues convincingly that life might have started more than once on our planet — and that microbes descending from another creation might still survive, either in an environment so hostile that it lies beyond the reach of all known life or else intermingled with conventional organisms but so far unrecognised. The discovery of a terrestrial “alien microbe”, with biochemistry so different from all known organisms that it must descend from a second start, would greatly increase the chance that life is plentiful throughout the universe.
The book finishes with biology’s most intensive information-processing centre, the human brain. Davies writes a good overview of the possibilities offered by information theory for solving “the number one problem of science”, consciousness, without coming to a clear conclusion.
The extent to which quantum physics can explain how and why we feel conscious is an open question but he feels that it must be involved, because quantum mechanics is our most powerful description of nature. Ultimately consciousness will either be explained by quantum theory or turn out to violate it — and in the latter case, the entire theoretical foundation of science will have to be rewritten.
The biggest question posed by The Demon in the Machine is whether bringing information into the equation adds something really new to the laws of nature, beyond current physics and chemistry, which theorists have not yet appreciated. Might some sort of informational laws be at work in complex systems, which somehow favour the emergence and evolution of life?
Whatever the answer, Davies has written an important and imaginative book. It is unlikely to change the course of science as much as Schrödinger’s What is Life? in the 1940s, but if it makes biologists more aware of the significance of information theory, it will at the least trigger some interesting new research.
The Demon in the Machine: How Hidden Webs of Information are Finally Solving the Mystery of Life, by Paul Davies, Allen Lane, RRP£20, 250 pages
Clive Cookson is the FT’s science editor
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