Seventy-five years ago the distinguished physicist Erwin Schrödinger published a celebrated book entitled What is Life? Despite dazzling advances in biology since, scientists still don’t know what life is or how it began. There is no doubt that living organisms are in a class apart, almost magical in their amazing properties. Yet they are made of normal matter. Just in the last few years, the secret of life is finally being revealed, and the missing link between matter and life comes from a totally unexpected direction. The discovery looks set to open up the next great frontier of science, with sweeping implications for technology and medicine. It also holds the tantalising promise of uncovering fundamentally new laws of nature.
Remarkably, What is Life? appeared at the height of the Second World War. Schrödinger had fled his native Austria to escape the Nazis and, after a brief sojourn in Oxford, settled in Dublin at the invitation of the Prime Minister, Eamonn de Valera, accompanied by both his wife and mistress. Ireland was a neutral country, so Schrödinger felt free to pursue his academic work, unlike many of his scientific colleagues who assisted the Allied war effort. Schrödinger was one of the founders of quantum mechanics, the most successful scientific theory ever. It explained at a stroke the properties of atoms, molecules, subatomic particles, nuclear reactions and the stability of stars; in practical terms it has given us the laser, the transistor and the superconductor. For de Valera, Schrödinger was quite a catch.
Away from his normal environment, Schrödinger permitted himself to explore new interests, turning his attention to biology. Quantum mechanics is notorious for being hard to understand. Yet for all his brilliance in crafting this esoteric branch of physics, the nature of life baffled him. Indeed, like many of his contemporaries, including Einstein, he thought that understanding how life works is a much tougher proposition than understanding quantum physics.
“Living things seem to possess innate purposes”
The problem of what makes living organisms tick has puzzled some of the best minds in history. The philosopher Aristotle put his finger on a key property two-and-a-half millennia ago. Living things seem to possess innate purposes or goals. It would make no sense to describe an atom or the moon as striving to achieve something, yet organisms behave this way all the time, battling for survival, seeking out mates, exploring new environments. Aristotle introduced the term ‘teleology’ to describe the tendency of living things to be drawn towards a future goal.
With the advent of the modern scientific era in the seventeenth century, physicists found no place for teleology. Isaac Newton envisaged a clockwork universe in which every particle of matter moved precisely in accordance with fixed universal laws, without regard to any destiny or purpose. Thus there opened up a vast chasm between physics and biology. So given that both non-living and living things are made of the same sorts of atoms, whence comes the inner drive of organisms?
It took about two hundred years for biology to begin catching up with physics, becoming a true science only with the publication of Darwin’s Origin of the Species in 1859. But whatever the greatness of the theory of evolution, it did nothing to close the gap with physics. Biologists concern themselves with what life does, not what it is. Although Darwin gave a convincing account of how life on Earth has evolved over billions of years from simple microbes to the richness and diversity of the biosphere we see today, he refused to be drawn in how life got going in the first place. ‘One might as well speculate on the origin of matter,’ he quipped to a friend. The transformation of matter from the realm of physics and chemistry to the realm of biology remained impenetrable.
Following Schrödinger‘s pointer, this state of affairs persisted until the middle of the twentieth century. Although historians disagree about the originality of Schrödinger’s ideas, there is no doubt that his book proved extremely influential ushering in the era of molecular biology in the early 1950s. Schrödinger surmised that genetic information must be stored in some sort of giant molecule. Following Schrödinger‘s pointer, Crick and Watson zeroed in on DNA and discovered its famous double-helix structure. They concluded that genes are segments of DNA in which information is encoded in the specific arrangement of atoms.
The informational part of DNA consists of four molecular building blocks, often referred to simply by the letters, A, C, T and G, constituting a four-letter alphabet. Sequences of these letters spell out the instruction manual for building the organism. The instructions are read out and implemented by complex molecular machinery with finely-honed control mechanisms. Because the instructions are in code, they must first be de-coded, or translated, by a mathematical procedure, before the cell can implement them. It took a few more years for scientists to crack the code and reveal the language of life, and several decades before DNA sequencing became commonplace.
The rapid progress made in molecular biology in the 1950s coincided with major advances in computing, and it was soon clear that the two subjects were intimately intertwined. DNA, which serves as a database storage facility, is like the hard drive on a computer. The instructions etched into DNA and the associated read-out and translation machinery resemble the operating system and software used by the computer industry.
It turns out that the analogy goes far deeper. Human DNA codes for about 20,000 genes, but only a fraction of them are ‘expressed’ at any one time. By expressed, I mean they get read out, causing a specific protein to be manufactured. Put simply, your genes are all there inside you, but they may be either ‘on’ or ‘off’ depending on circumstances. Genes are often linked via chemical messengers because a protein coded for by one gene may serve to switch others on or off. In this way, genes can form networks, sometimes of great complexity. It is the networks, rather than individual genes, that carry out the lion’s share of regulatory and control functions. In this respect, biology closely resembles electronics. Biologists routinely refer to the ‘wiring diagram’ of gene networks, and have discovered that some arrangements form modules that can behave like the logic gates in a computer; by wiring together many such gates, cells are able to carry out complex computations.
Why is life invested in the business of computing? The answer is that most organisms live in an unpredictable and fluctuating environment, and the ability of cells to garner information from their surroundings, process it, and compute an optimal response, confers an obvious survival advantage. And it is not just individual cells that process information. Cells can signal each other with both chemical messengers and physical forces, enabling them to cooperate. This is particularly striking in multi-celled life forms, in which pathways of information flow pervade the entire organism. Nor does it stop there. Signals can also be exchanged between organisms, for example, when ants or bees engage in collective decision making choosing a nest, or when flocking birds coordinate their flight. Even ecosystems possess elaborate networks of information flow. Earth’s biosphere is the original World Wide Web.
Is Extinction Bad? Read more Today, biologists routinely frame their descriptions of life in informational terms. Concepts like the genetic code, gene sequence transcription and translation, signalling molecules, regulation and control, and logic functions all stem directly from the world of computing and information processing. Familiar that may be, but it is not at all the language used by physicists and chemists. Ask them, ‘What is life?’ and you are likely to be told about molecular shapes and binding energies, reaction rates, intermolecular forces and heat production.
The mismatch of these two descriptions is stark, but because biology and physics are pretty thoroughly siloed it is rarely problematic. Nevertheless, although twin parallel narratives might pass muster for most purposes, when it comes to the origin of life – when physics and chemistry somehow turned into biology – then without a conceptual thread that links them no explanation can be forthcoming.
How on Earth can a haphazard mish-mash of chemicals spontaneously organise itself into a system that stores digital information and processes it using a mathematical code? Barring a stupendously improbable freak accident, there are only two possible answers. The first is some sort of divine intervention – intelligent design. The second is a fundamentally new type of organising principle at work in complex systems.
When Schrödinger wrote his book he addressed the question of whether life, with all its remarkable properties, could ever be explained by known physics. He boldly left open the possibility that new laws of nature may be required. His suggestion has always been regarded as deeply heretical: the standard view is that known physics can explain everything. In my opinion that is just wishful thinking, a type of promissory reductionism. In truth, standard physics and chemistry have spectacularly failed to explain life’s origin. What little progress has been made in synthesising some small chemical components of life has always required an intelligent designer (aka a clever scientist), and a fancy lab. More seriously, nobody has a clue about how this freshly-minted organic hardware can create its own software. How can molecules write code?
“In quantum systems uncertainty is not just the result of human ignorance: it is inherent in it, a basic feature of nature”
If there are indeed hitherto undiscovered ‘laws of life’ connecting biology and physics, information and matter, software and hardware, then this missing link needs to assign to information some sort of causal role or traction over physical states, in order to make a difference. But information is an abstract concept that derives from the realm of human discourse. Can it also be a physical quantity? That is, can it carry clout when it comes to material objects? It turns out that the answer is yes.
Scientists have a formal definition of information as the reduction in uncertainty or ignorance resulting from an observation as, for example, the outcome of a coin toss is inspected.. But in quantum systems the uncertainty is not just the result of human ignorance: it is inherent in it, a basic feature of nature. Thus information lies at the very heart of quantum physics.
In recent years scientists have found tantalising hints that life is exploiting quantum effects in some specific cases, including photosynthesis and bird navigation. The controversial subject of quantum biology is attracting much attention. Most intriguing from my point of view are the experiments of Gabor Vattay of Eötvös Loránd University, Budapest, who has found evidence that many key molecules used by life have unusual finely-tuned quantum properties. One explanation is that evolution has selected these properties for reasons of chemical efficiency. But a more intriguing possibility is that the special characteristics of these molecules relates to the transfer and organisation of information – a hidden quantum code – and that it is at the level of these large organic molecules that the new principles I have been advocating are manifested.
The next frontier of science lies at the intersection of nanotechnology, quantum physics, chemistry and biology. It is here, where physics meets life, that unexpected new phenomena will be discovered, and Schrödinger’s 75 year old question will finally be answered.