A melding of biology and physics first suggested in the 1920s is enjoying a revival as evidence mounts. Stephen Fleischfresser reports.
An old and quirky collaboration between seemingly incompatible scientific fields is producing fascinating new insights into the nature of the living world.
Meet the discipline known as “quantum biology”: the idea that the oddities of quantum mechanics such as entanglement, quantum tunnelling, superposition of wave states, the uncertainty principle and quantum coherence play vital roles in the biology of living things.
The concept of “interdisciplinarity” is all the rage in academia these days: widely divergent fields come together to hybridise their insights and find new ways of seeing the world.
And this makes sense: logically speaking, if there is a seamless web of causality in the world, then scientific fields must intersect and overlap in numerous places.
Quantum biology is one such meeting point. And while it is producing remarkable and novel findings about olfaction, photosynthesis and the action of enzymes, the interdiscipline is as old as the quantum revolution itself.
Johnjoe McFadden, a molecular geneticist and writer, and Jim Al-khalili, a theoretical physicist and broadcaster, both from the University of Surrey in the UK, trace the history of quantum biology in a new paper in the journal Proceedings of the Royal Society A.
Although the origin of quantum biology is often thought to be Erwin Schrödinger’s 1944 publication What is Life?, the field actually dates back to the late 1920s, just as the mathematical underpinnings of quantum mechanics were established.
Biology in the early twentieth century was still torn between two philosophical outlooks. The first was the mechanistic worldview of the Scientific Revolution: in particular, Rene Descartes’ theory that organisms were not much more than soulless machines.
The other was the notion of “vitalism”, which took the spotlight in the early nineteenth century. This was the belief that there was something fundamentally different and even mysterious about living organisms, and that their function and make-up could not be reduced to mere classical chemistry and physics. Some vital spark, or élan vital, marked life from non-life.
A third way emerged: organicism. The leading light of this philosophical movement was the Austrian biologist Ludwig von Bertalanffy, famous for the development of general systems theory. As much a synthesis as a rejection of both mechanistic thinking and vitalism, organicism, write McFadden and Al-khalili, “accepted that there was something mysterious about life but claimed that the mystery could in principle be explained by the laws of physics and chemistry — it is just that these had to be new laws, as yet undiscovered".
The newly formulated quantum mechanics seemed like the perfect candidate for these new laws.
As early as 1929, Niels Bohr was making vague allusions to the role of quantum thinking in biology, and although such a vision was not yet fleshed out by Bohr himself, he inspired others.
In particular, the German physicist Pascual Jordan maintained correspondence with Bohr and published the culmination of their considerations in the first true paper on quantum biology: Quantum mechanics and the fundamental problems of biology and psychologypublished in the German journal Die Naturwissenschaften in 1932.
He postulated that the new laws sought by organicist philosophy were “the rules of chance and probability (the indeterminism) of the quantum world that were somehow scaled up inside living organisms". He called this the “amplifier theory”.
Jordan continued publishing on the topic and was using the term quantenbiologie, or quantum biology, from the 1930s onwards. Unfortunately for the reputation of the science, Jordan became fully committed to the rising Nazi ideology in Germany and his scientific work became increasingly politicised. This contributed to a later lack of enthusiasm for quantum biology more generally.
Bohr returned to the topic, too, this time arguing that complimentarity, or wave-particle duality (the idea that quantum objects act as both particles and waves, but never both at the same time) was the organicist “new law” that would uncover the mysteries of the living world. Together with Werner Heisenberg, Bohr wondered if such quantum phenomena played an undiscovered role in the mutation and selection of Darwinian evolution.
In the 1940s Erwin Schrödinger argued that genes and the laws of heredity were sensitive to quantum mechanical dynamics and that the mutations necessary for natural selection arose through quantum tunnelling (the phenomena whereby subatomic particles can reach lower energy states by bypassing, or tunnelling through, intervening higher energy states).
These musings in What is Life? partly inspired Francis Crick and James Watson to investigate the nature and structure of genes.
However, with the incredible breakthroughs in molecular biology that were to follow, much of life’s mechanics were explained using classical chemistry, without recourse to quantum phenomena.
Further reflection in physics pointed out that much of the interesting aspects of quantum mechanics depended on a system being completely isolated from its environment, which was particularly unlikely, McFadden and Al-khalili note, in the “hot, wet and complex system in such a living cell”. By the 1960s quantum biology slumped, with most researchers being “dismissive of the notion that quantum mechanics played any kind of special role in living systems”.
Several scientists kept thinking about the connection between quantum mechanics and life, however, with some, such as British mathematical physicist Roger Penrose, even drawing connections between the quantum world and consciousness. But for the most part, many of the early claims of quantum biology were discredited and the classical sciences remained dominant in biology.
However, in the past few decades quantum biology has experiencing something of a revival. There is now, the authors state, “sound experimental evidence for quantum coherence in photosynthesis and quantum tunnelling in enzyme action; together with strong theoretical arguments and some experimental evidence supporting the role of quantum entanglement in avian navigation and quantum tunnelling in olfaction".
There are also some tantalising findings to suggest that the “hot, wet and complex” biological systems, non-equilibrium systems fundamentally connected to their environment, might actually promote interesting quantum dynamics, rather than rule them out has had been thought in the sixties.
The question has now become how quantum phenomena affect biology, rather than if they do. And given that evolution has had three and half billion years to devise ways to harness the oddities of quantum mechanics, there seems much for quantum biology to explore.
“They may have had to wait many decades,” write the authors, “but the quantum pioneers were indeed right to be excited about the future of quantum biology.”
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