AN INTRODUCTION TO QUANTUM BIOLOGY

Quantum physics completely revolutionised how we viewed reality. That wacky, bizarre and strange field concerning the very small stemmed from the luridly imaginative minds of several early 1920s scientists—whether it be Erwin Schrödinger and his simultaneously dead-yet-somehow-alive cat, Werner Heisenberg and his uncertainty principle regarding a particle’s position and momentum, or the French physicist Louis de Broglie’s declaration that all matter possesses wave-particle duality—and has captured the imagination of many. Welcome to the weird, wonderful world of superposition, entanglement, the wave function (which is often represented with the Greek letter Ψ) and where the debate among keen science enthusiasts rages on. As such, these radical ideas challenged the classical Newtonian physics which had dominated for over the prior two centuries. They were so contrary to common sense that even the eminent American theoretical physicist Richard Feynman remarked, “I think I can safely say that nobody understands quantum mechanics.” Of course, Feynman isn’t denying that anybody has made a genuine and fruitful inquiry into the tenets of quantum physics—instead, he is expressing how utterly peculiar and unusual quantum mechanics truly is. Thus, many think that quantum physics is an arcane and esoteric field of science which has no applications in the “real world,” supposedly exclusively dominated by the more familiar fields of biology, chemistry and the earth sciences.

However, this commonly-held assumption is now being challenged by an emerging field of research. Quantum biology, as it is called, could provide the answers to some of the most fundamental questions concerning life. It has been shown to play a role in photosynthesis, how birds migrate, how enzymes act as biological catalysts and the genetic mutations driving evolution and disease. To be precise, quantum biology is a sub-branch of biophysics which attempts to incorporate quantum mechanics into explanations of how biological systems function or operate in which classical biology is unable to provide a fully adequate account of. As the biophysicist G. S. Engel states,

Quantum biology involves the search for (and subsequent study of) these manifestly quantum effects in biological systems. . . . In my opinion, a central goal of quantum biology must be to elucidate new design principles underlying biological systems and to demonstrate this understanding by applying these ideas to synthetic system. This is not merely an academic endeavor—new design principles will likely spawn new devices and technology as well as an improved understanding of basic science. Quantum effects in biology have been posited in olfaction, magnetic sensing, photosynthetic energy transfer, photoenzymology, molecular motors, ion channels and even consciousness.^[1]

To begin, let us explore the idea of quantum entanglement I mentioned at the beginning. In quantum entanglement, two particles, however far apart they are from each other—be they a nanometre or one light year apart—are linked to each other in such a manner that the mathematical description of the quantum state of one particle (this description we call the wave function) provides us information about the other particle. The great Albert Einstein, with his loathsome attitude towards quantum theory, famously dubbed this phenomenon “spooky action at a distance.” Yet, contrary to Einstein, quantum entanglement is real and was recently empirically confirmed by Dutch physicists experimenting with electrons in diamonds separated between two laboratories. “So what about entanglement and Dutch diamond electrons?” one may ask.

Surprisingly, the exact same mechanism is germane to how birds sense the earth’s geomagnetic field—called magnetoreception—in order to migrate unbelievably vast distances. A notable example is the European robin, or robin redbreast—a small, insectivorous bird—which navigates from Scandinavia down towards the Mediterranean Sea adjacent to North Africa every winter, often traversing distances of up to thousands of kilometres. How does it manage this impressive feat?  Within the robin's retina is a light-sensitive chemical protein called cryptochrome, which upon being exposed to a photon of sunlight, releases two entangled electrons. The two electrons dance a dance which is influenced by the direction that the bird flies relative to the magnetic field. While much evidence has accumulated in favour of this explanation, there is much we still do not understand regarding the robin’s remarkable magnetoreception.

Furthermore, quantum entanglement is theorised to be the very force holding the code of life itself intact. Of course, that “code of life” is nothing but a reference to deoxyribonucleic acid, or DNA. In 2010, a paper published by several scientists proposed a simplified theoretical model of DNA in which each of the building blocks of DNA—named nucleotides—is comprised of a negative electron cloud surrounding a central positive nucleus. The cloud’s movement in backward and forward directions is characteristic of a harmonic oscillator, whereas its movement being relative to the inner nucleus represents a dipole. When nucleotides bond, their clouds oscillate in opposite directions in order to provide stability to the resulting base pair. These oscillations manifest themselves in what is known as a quantum superposition of states—when two or more different quantum states are combined (“superposed”) together to form another new quantum state—meaning that they oscillate in all different possible states. To quote from the authors of the original paper,

We model the electron clouds of nucleic acids in DNA as a chain of coupled quantum harmonic oscillators with dipole-dipole interaction between nearest neighbours resulting in a van der Waals type bonding. . . . We find that the strength of the single base von Neumann entropy depends on the neighbouring sites, thus questioning the notion of treating single bases as logically independent units. We derive an analytical expression for the binding energy of the coupled chain in terms of entanglement and show the connection between entanglement and correlation energy, a quantity commonly used in quantum chemistry.^[2]

However, quantum biology has provided other equally fascinating insights into DNA. Inside the human cell are certain enzymes which are remarkably adept at replicating DNA molecules by pairing up the correct bases—adenosine + thymine and cytosine + guanine, of course—and discarding incorrect base pairs. Nonetheless, these enzymes do occasionally err, and such intermittent errors are believed to account for around 2/3 of cancerous mutations in humans. However, why do enzymes commit these seemingly random errors in the first place? Francis Crick and James Watson, the very fathers of DNA themselves who first discovered the double helix geometry of DNA in 1953, hypothesised that the DNA bases undergo spontaneous transformations into different states which trick the enzymes into replicating incorrect base pairs, opening the door for the possibility of such errors. Problem is, nobody had witnessed these spontaneous transformations—that is until Duke University researchers observed DNA temporarily mimicking the structures of different bases by the shifting or altogether sequestration of atoms. This transitory mimicking is referred to as a quantum jitter, and could potentially be the basis for evolutionary development and diseases.

As a final example, the quantum world is deeply woven into the process of photosynthesis, whereby plants convert carbon dioxide and water into starch and sugars via the sun’s energy. The plant gathers the sun’s photons by its chromophores—a group of chemicals which confers colour onto molecules—located within the organelles—called chloroplasts—inside the plant’s cell. In turn, the chromophores release excitons—quasi-particles which are a combination of an electron and a positively-charged hole—which harness and transport the photons’ energy to the photosynthetic reaction centre. Here, the familiar green pigment chlorophyll is found, and the photon is converted into chemical energy which the plant is able to metabolise. This intricate process occurs in approximately one-trillionth of a second and can retain around 95% of the original energy as a result of the unmitigated speed of the photosynthetic process, thus, preventing much energy loss in the form of dissipated heat. However, how that unmitigated speed is executed by plants has remained largely elusive—until an experiment lead by G. S. Engel and his colleagues shed significant light on the mystery.

Engel’s team discovered that the excitons do not merely travel down one pathway, but simultaneously try multiple pathways instead in order to select the one which is most efficient—a clear case of quantum superposition. The experiment in question was performed on Chlorobium tepidum—a green sulphur bacterium found in New Zealand hot springs—cooled down to -196ºC and exposed to short bursts of concentrated pulsar laser light and electronic spectroscopy radiation. Interestingly, the experiment detected wavelike motion among the photons, which is due to the wave-particle duality of light, whereby light can behave as both a wave and as a particle. (This is reminiscent of the famous double-slit experiment, where the particle electrons fired formed an interference pattern characteristic of a wave.) Albert Einstein and Leopold Infeld commented on this peculiar property,

But what is light really? Is it a wave or a shower of photons? There seems no likelihood for forming a consistent description of the phenomena of light by a choice of only one of the two languages. It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.^[3]

Thus, the biochemical process which absorbs a total of around 10¹⁷ joules of solar energy bathing the earth every second has a hidden quantum nature. As Engel writes, 

Quantum coherence improves the quantum efficiency of excitonic energy transport within the Fenna-Matthews-Olson photosynthetic complex from the green sulphur bacterium, Chlorobium tepidum. Experimental evidence from third-order nonlinear spectroscopies provides clear evidence of quantum coherence among excited states persisting for picoseconds despite rapid . . . dephasing of quantum coherence between ground and excited states. ^[1]

So, there you go: a brief introduction to the fascinating world of quantum biology, and ways it has illuminated our understanding of (1) how birds migrate; (2) how stability is conferred onto DNA; (3) the genetic mutations underlying evolution and disease; and (4) the remarkable efficiency of photosynthesis. However, whatever is to become of quantum biology’s current theories—whether corroborated or disconfirmed in the future—we can be confident that quantum biology has far more in store to reveal to us than what has already been revealed insofar as the previous decade has scientifically progressed. The old notion that quantum mechanics is too strange and counterintuitive to correspond to reality is dead. Allow me to end on a quotation of Sir Arthur Eddington, the English astronomer who famously confirmed Einstein’s general theory of relativity: “Not only is the universe stranger than we imagine, it is stranger than we can imagine.”

^[1] Engel, G. S. (2011) 22nd Solvay Conference on Chemistry Quantum coherence in photosynthesis. Available at: https://core.ac.uk/download/pdf/82787511.pdf (Accessed: 13 September 2018).

^[2] Rieper, E., Anders, J. and Vedral, V. (2010) Quantum entanglement between the electron clouds of nucleic acids in DNA. Available at: https://arxiv.org/pdf/1006.4053.pdf (Accessed: 13 September 2018).

^[3] Einstein, A. and Infeld, L. (1938) The Evolution of Physics. Cambridge: Cambridge University Press.