By Vince Giuliano
Minor update 7 July 2016. The field of quantum biology contines to fascinate me and I will brobably soon produce a second blog related to this area since there have been several relevant publications since I first drafted this item some 5 years ago in 2011. For the moment I mention only a 2013 survey publicaation Quantum biology. This publication refers mainly to topics covered in this blog. “Recent evidence suggests that a variety of organisms may harness some of the unique features of quantum mechanics to gain a biological advantage. These features go beyond trivial quantum effects and may include harnessing quantum coherence on physiologically important timescales. In this brief review we summarize the latest results for non-trivial quantum effects in photosynthetic light harvesting, avian magnetoreception and several other candidates for functional quantum biology. We present both the evidence for and arguments against there being a functional role for quantum coherence in these systems.”
The purpose of this blog entry is to provide an introduction to Quantum biology, an emerging new frontier in biology. Quantum biology strives to provide understanding of biological phenomena not explicable in any other existing framework. For at least one phenomenon, photosynthesis, it appears to be doing so in a way consistent with experimental results. There is also strong theoretical and circumstantial evidence that Quantum biology can provide very valuable insights in a number of other areas including the functioning of DNA, neural processing, the migratory patterns of some birds and the sensing of smells. The field is relatively unexplored and future applications may be without limit.
Most of the work in the Quantum biology field seems to have been originated by physicists and mathematicians rather than by biologists. This is not surprising given the complex mathematical training required to be fluent in matters related to quantum mechanics. Quantum biology suffers from one severe problem: mainly that biology is a massively complex system whereas quantum mechanics is massively deep(ref). But perhaps a combination of that depth and complexities can lead us to a whole world of new insights. This blog entry offers an introduction to quantum biology and links to several other resources useful for learning more about it.
Quantum physics and macroscopic reality
Well over a century old now, quantum physics (known also as quantum theory or quantum mechanics) was developed to explain physical phenomena on the atomic and subatomic level. I studied it many years ago as an area of graduate-studies concentration required for me to get my Ph.D. at Harvard “Quantum mechanics is the body of scientific principles which attempts to explain the behavior of matter and its interactions with energy on the scale of atoms and atomic particles. — Just before 1900, it became clear that classical physics was unable to model certain phenomena. Coming to terms with these limitations led to the development of quantum mechanics, a major revolution in physics — Some aspects of quantum mechanics can seem counter-intuitive, because they describe behavior quite different than that seen at larger length scales, where classical physics is an excellent approximation. In the words of Richard Feynman, quantum mechanics deals with “nature as she is — absurd.” (ref)”
The mathematical apparatus of quantum physics is well experimentally validated and without question works as a pillar of current science and engineering. However, both physicists and philosophers have been flummoxed over a century now by the extremely strange views of reality imposed by quantum physics. Many different schools of interpretation of quantum physics exist, each school with its own proponents. Depending on the school of interpretation, objects do not have definite properties until they are observed and all matter behaves both as waves and particles (Copenhagen interpretation), or reality consists of wave functions spanning an unfolding infinite manifold of parallel universes (many worlds interpretation), or the present communicates instantly with the past and future to create an outcome in the present (Cramer’s transactional interpretation), or the physical universe is not really real; there is only the quantum universe which is like an infinite collection of classical universes (zero universe interpretation).
Regardless of school, in quantum physics there are many new strange concepts to take into account including Superposition, Entanglement, Complementarity, Duality, Uncertainty , Exclusion, Decoherence, Ehrenfest theorem,Tunnelling, and Nonlocality. Nonlocality, for example, implies that action at one point can produce an effect even far across the universe. This is not via a signal traveling at the speed of light. It is an instantaneous effect. It is because far-apart objects like a photon pair flying in opposite directions from a single source may be correlated, that is, just aspects of a single super-object. So that doing something to one part of the super-object like polarizing the photon instantly polarizes its correlated sister well no matter how far away it may be. In a famous thought experiment, Schrodinger’s cat is both dead and alive at the same time. Sounds nuts? It is. As a graduate student I had many weird dreams before I could start to accept the quantum theory’s profound messages about how unreal reality really is.
For most of the last 110 years the conventional wisdom has been that quantum effects only exist on the atomic and subatomic scale and that on a normal scale things function according to the good-old-laws of classical physics which are completely consistent with our experience of how things work. It was thought that biological systems are so complex, warm, and subject to random effects that they can’t be coherent and therefore we don’t have to worry about quantum weirdness when it comes to biology.
This thinking is, simply put, wrong. To start with, although quantum phenomena starts out on the atomic and subatomic scales, the impact of these phenomena on the macroscopic scale can be and obviously has been immense. Think, for example, about nuclear bombs and nuclear energy, transistors and integrated circuits, lasers, superconducting fluids, computers, smartphones and hearing aids just to start the list. All of these depend on underlying quantum phenomena. And strange quantum behavior like entanglement is being observed in more and more big ordinary-scale systems. An interesting article addressing this point just appeared in the May 2011 issue of Scientific American: Living in a Quantum World “Quantum mechanics is not just about teeny particles. It applies to things of all sizes: birds, plants, maybe even people.”
“Quantum biology refers to applications of quantum mechanics to biological objects and problems. Usually, it is taken to refer to applications of the “non-trivial” quantum features such as superposition, nonlocality, entanglement and tunneling, as opposed to the “trivial” applications such as chemical bonding which apply to biology only indirectly by dictating quantum chemistry. — Erwin Schroedinger is one of the first scientists to suggest a study of quantum biology in his 1946 book “What is Life?” — Some examples of the biological phenomena that have been studied in terms of quantum processes are the absorbance of frequency-specific radiation (i.e., photosynthesis and vision); the conversion of chemical energy into motion; magnetoreception in animals and brownian motors in many cellular processes.” (ref)
To repeat a point, there is an obvious sense in which biology depends on quantum physics: biology depends on molecules which are formed from combinations of atoms which combine according to electron energy states in various electron orbits according to rules determined by quantum chemistry which explains how molecules are formed and behave. There are things to be considered like resonant electrons which have quantum properties and exist in more than one place at a time. But these spooky electrons remain tucked away out of sight. So biological entities would not exist without quantum physics. If fact, nothing would. So please folks, stop saying quantum physics just affects the very tiny and is irrelevant to biology. If you believe that, try sitting next to an exploding atomic bomb.
The central issues of quantum biology are 1. Clarifying where strange quantum effects are key in driving biological development and activities, that is, where quantum explanations can provide explanations for matters otherwise unexplainable, and 2. Using those understandings to further our interests as humans. Possible examples could be in drug development, facilitation of pollution-consuming ocean bacteria, and development of highly efficient solar cells based on quantum effects utilized in plant leaves.
So, what about strange quantum phemenona? Can these or their effects be observed in plants, animals and people? Yes. I will discuss several known examples of this although there are probably many more yet to be discovered.
An introduction to quantum biology is captured in the introductory video from a Google Workshop on Quantum Biology. See also the fun and informative video presentation Seth Lloyd on Quantum Life. And the video The Quantum Conspiracy: What Popularizers of QM Don’t Want You to Know lays out an innovative interpretation of quantum mechanics from the viewpoint of a creative software engineer, called the zero-universe interpretation.
Quantum physics and DNA
The central news appears to be that neighboring molecular sites in DNA exist in a state of quantum entanglement. Further, because entanglement can exist between neighboring sites, it can exist among molecules along a whole chain of DNA. This affects the very nature of their identity as well as their ability to consistently store and process information. Mutations, for example, can result from quantum uncertainty and tunneling. In addition to classical information embedded in DNA, there is quantum information which behaves according to its own characteristics. For example, communication channel capacity between two systems which are entangled can be much higher, about double that between similar systems which are not entangled. Is this property of quantum information used to enhance information communication along strands of DNA? While a definitive answer is not in, there appears to be good circumstantial evidence to support the conjecture.
Here are a few of the central concepts extracted from the video presentation Classical and Quantum Information in DNA (Google Workshop on Quantum Biology): A central role of DNA is the long-term storage of information. Entropy in classical Shannon Weaver information theory describes information as negative entropy, entropy being a measure of ignorance about a system. Zero entropy means you know everything about it.
Quantum information, on the other hand, is defined by a variant of this formula but has strikingly different properties: quantum information cannot be read, copied or cloned copied because, in a coherent state, a system is in a state of superposition of multiple values with unknown outcomes. Reading or copying the information involves entanglement between physical media entailing decoherence. On the other hand, the potentials for processing quantum information are far greater than those for classical information. Thus quantum computing makes “direct use of quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data.”
How do quantum effects impact on DNA? There appears to be a multiplicity of possible ways:
· Some DNA Mutations may be due to proton quantum tunneling(ref). For example, the quantum tunneling of a proton in cytosine to a different energy state could make that molecule not be available for binding to guanine resulting in it binding to cytosine instead.
· Local DNA sites have knowledge of their neighbors; they are entangled. This is because neighboring electron crowds repel each other resulting in correlated excitations and lower ground state energy and coherence resulting in classical Van Der Waals forces. The electron cloud in one site carries information about the identity of its neighboring site. This means that the very identity of molecules in DNA is influenced by its neighbors.
· Entanglement and correlation can exist along a whole chain of DNA. An implication could be significant increase in the capacity to transfer information along a chain of DNA.
· The information necessary for proper protein folding is not present in the linear sequences of source DNA. A possibility is that it is encoded as quantum information. You can find additional videos on the topic here.
Quantum entanglement exists in DNA
Quantum entanglement of two objects implies that quantum properties of the two objects are bound together even if the objects are far apart. You can’t change one without changing the other as well. More formally: “Quantum entanglement is a property of the state of a quantum mechanical system containing two or more degrees of freedom, whereby the degrees of freedom that make up the system are linked in such a way that the quantum state of any of them cannot be adequately described independently of the others, even if the individual degrees of freedom belong to different objects and are spatially separated(ref).”
The 2011 publication Quantum entanglement between the electron clouds of nucleic acids in DNA reports “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. Crucial parameters in our model are the distances between the acids and the coupling between them, which we estimate from numerical simulations . We show that for realistic parameters nearest neighbour entanglement is present even at room temperature. We quantify the amount of entanglement in terms of negativity and single base von Neumann entropy. 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.” (Italic emphasis is my own).
The paper concludes: “ In this paper we modeled the electron clouds of nucleic acids in a single strand of DNA as a chain of coupled quantum harmonic oscillators with dipole-dipole interaction between nearest neighbours. Our main result is that the entanglement contained in the chain coincides with the binding energy of the molecule. We derived in the limit of long distances and periodic potentials analytic expressions linking the entanglement witnesses to the energy reduction due to the quantum entanglement in the electron clouds. Motivated by this result we propose to use entanglement measures to quantify correlation energy, a quantity commonly used in quantum chemistry. As the interaction energy given by ~Ï‰ is roughly 20 times larger than the thermal energy kB300K the motional electronic degree of freedom is effectively in the ground state. Thus the entanglement persists even at room temperature. Additionally, we investigated the entanglement properties of aperiodic potentials. For randomly chosen sequences of A,C,G, or T we calculated the average von Neumann entropy. There exists no direct correlation between the classical information of the sequence and its average quantum information. The average amount of von Neumann entropy varies strongly, even among sequences having the same Shannon entropy. Finally we showed that a single base contains information about its neighbour, questioning the notion of treating individual DNA bases as independent bits of information.” The implications seem to be:
· Neighboring base pairs in a DNA sequence are entangled and cannot be considered independently
· This entanglement takes place at ordinary body temperature
· Information-theory measures of information in a sequence of DNA are very different when viewed from a quantum or classical viewpoint.
Other theoretical and modeling studies related to quantum properties of DNA are Polaronic transport through DNA molecules (2010) and Conductance of DNA molecules: Effects of decoherence and bonding (2010).
Photosynthesis depends critically on quantum effects
Leaves on trees and plants are highly sophisticated yet extremely cheap device that convert solar radiation into stored forms of energy. Part of the process happens with over 99% efficiency and involves coherence, a quantum effect where particles called excitons behave as waves to get quickly from where they are knocked loose by incoming light photons to a destination molecular energy storage center. The effect was discussed in the 2001 publication Bacterial photosynthesis begins with quantum-mechanical coherence. “In the antenna system of photosynthetic bacteria, pigments form circular aggregates whose excitations are excitons with quantum-mechanical coherence extending over many pigments. These excitons play crucial roles in light harvesting, storage, and excitation-energy transfer (EET). EET takes place rapidly to and/or from optically forbidden exciton states, without total transition dipole, within the antenna system and to the reaction center. Such EETs cannot be rationalized by FÃ¶rster’s formula, the traditional theory on EET, because it allows EET only between optically allowed states. The coherence in the excitons seems to prohibit rapid EET on this formula. The bacteria overcome this difficulty by circumventing the coherence, using the effects of the physical size of an aggregate that is larger than the shortest distance between pigments in the donor and pigments in the acceptor. The shortest-distance pair therein cannot detect whether the aggregate has a nonvanishing total transition dipole or not, since the pair see effectively only the transition dipole on the other pigment in themselves. The transition dipole facilitates rapid EET even to and/or from optically forbidden exciton states.”
An important 2007 publication Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems reports “Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke ‘hopping’ of excited-state populations along discrete energy levels1, 2. Two-dimensional Fourier transform electronic spectroscopy3, 4, 5 has mapped6 these energy levels and their coupling in the Fenna–Matthews–Olson (FMO) bacteriochlorophyll complex, which is found in green sulphur bacteria and acts as an energy ‘wire’ connecting a large peripheral light-harvesting antenna, the chlorosome, to the reaction centre7, 8, 9. The spectroscopic data clearly document the dependence of the dominant energy transport pathways on the spatial properties of the excited-state wavefunctions of the whole bacteriochlorophyll complex6, 10. But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses—even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago11, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted12, 13 and indirectly observed14. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77 K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.”
Put in simple terms, by behaving as waves rather than particles, excitons can move to where they need to go in the bacteriochlorophyll complex by following all possible paths simultaneously. They don’t have to dodge around a multiplicity of molecules to get there as particles behaving as classical particles would. This time it is quantum coherence doing the job. Quantum coherence refers to a system being in a condition of multiple possible states where the actual state corresponding to an observable reality is unresolved and unknowable. “A quantum state is often a superposition of other quantum states, for instance, the spin states of an electron. Simply put; the electron can assume or occupy numerous states simultaneously. These unique states are then referred to as a spectrum of eigenstates, or allowed conditions. In the Copenhagen interpretation, the superposition of states was described by a wave function, and the wave function collapse was given the name decoherence. Today, the decoherence program studies quantum correlations between the states of a quantum system and its environment. But the original sense remains: decoherence refers to the untangling of quantum states to produce a single macroscopic reality. ” (ref)
A number of other studies followed this one amplifying on and extending its findings, most highly mathematical. For example, the 2008 paper Environment-Assisted Quantum Walks in Photosynthetic Energy Transfer looks at the quantum-based photosynthesis energy transfer process as it might apply more generally in large molecules and explains further its remarkable efficiency. “Energy transfer within photosynthetic systems can display quantum effects such as delocalized excitonic transport. Recently, direct evidence of long-lived coherence has been experimentally demonstrated for the dynamics of the Fenna-Matthews-Olson (FMO) protein complex [Engel et al., Nature 446, 782 (2007)]. However,
the relevance of quantum dynamical processes to the exciton transfer efficiency is to a large extent unknown. — Here, we develop a theoretical framework for studying the role of quantum interference effects in energy transfer dynamics of molecular arrays interacting with a thermal bath within the Lindblad formalism. To this end, we generalize continuous-time quantum walks to non-unitary and temperature-dependent dynamics in Liouville space derived from a microscopic Hamiltonian. Different physical effects of coherence and decoherence processes are explored via a universal measure for the energy transfer efficiency and its susceptibility. In particular, we demonstrate that for the FMO complex an effective interplay between free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in energy transfer efficiency from about 70% to 99%.”
The2009 paper Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature further explores and confirms the earlier findings “The observation of long-lived electronic coherence in a photosynthetic pigment–protein complex, the Fenna–Matthews–Olson (FMO) complex, is suggestive that quantum coherence might play a significant role in achieving the remarkable efficiency of photosynthetic electronic energy transfer (EET), although the data were acquired at cryogenic temperature [Engel GS, et al. (2007) Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature 446:782–786]. In this paper, the spatial and temporal dynamics of EET through the FMO complex at physiological temperature are investigated theoretically. The numerical results reveal that quantum wave-like motion persists for several hundred femtoseconds even at physiological temperature, and suggest that the FMO complex may work as a rectifier for unidirectional energy flow from the peripheral light-harvesting antenna to the reaction center complex by taking advantage of quantum coherence and the energy landscape of pigments tuned by the protein scaffold. A potential role of quantum coherence is to overcome local energetic traps and aid efficient trapping of electronic energy by the pigments facing the reaction center complex.” Among other publications treating this subject are:
A 2010 graphical PDFpresentation with associated mathematical representations is Photosynthetic Light Harvesting and Electronic Quantum Coherence.
A graphical PDF presentation about how the quantum light-harvesting process works in purple bacteria is here. “Purple bacteria or purple photosynthetic bacteria are proteobacteria that are phototrophic, that is capable of producing energy through photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids. These give them colours ranging between purple, red, brown, and orange(ref).”
Finally, if you want to hear even more about quantum effects in photosynthesis, you can view the video lecture Photosynthesis – quantum life.
Note that to function comfortably in the field of quantum biology a scientist must be able to go back and forth between two languages and thinking systems: the highly mathematical systems of both classical and quantum physics and the molecular and conventional biology perspectives and jargon used in the biology research literature and reflected in many entries in this blog.
Quantum Physics and Neuroscience
The relationship between quantum physics and neuroscience has an entangled history deeply connected with whether consciousness is an emergent quantum-based phenomenon. So, first, I need to identify and set aside discussion of the possibility of quantum consciousness a fascinating subject that has drawn the attention of scientists, philosophers and mystics, including much skepticism. There is a substantial literature connected with quantum consciousness, but I can’t really get deeply into that subject here without it being a gigantic detour. Some papers like Quantum squeezed state analysis of spontaneous ultra weak light photon emission of practitioners of meditation and control subjects strive to present serious scientific investigations relating to quantum consciousness. Some other traditional hard scientists see such topics as irrelevant or as mystic nonsense. A 2002 article [Quantum mechanics and brain: a critical review].concluded “As currently exposed, the three QM theories of consciousness suffer from important neuroscientist concerns. It is not necessary the use QM to explain different aspects of brain function such as consciousness, which would be better understood using tools from the neurosciences. However, I do cite a few recent papers related to quantum neural phenomena, again mostly theoretical in nature.
The 2011 paper Emission of mitochondrial biophotons and their effect on electrical activity of membrane via microtubules reports “In this paper we argue that, in addition to electrical and chemical signals propagating in the neurons of the brain, signal propagation takes place in the form of biophoton production. This statement is supported by recent experimental confirmation of photon guiding properties of a single neuron. We have investigated the interaction of mitochondrial biophotons with microtubules from a quantum mechanical point of view. Our theoretical analysis indicates that the interaction of biophotons and microtubules causes transitions/fluctuations of microtubules between coherent and incoherent states. A significant relationship between the fluctuation function of microtubules and alpha-EEG diagrams is elaborated on in this paper. We argue that the role of biophotons in the brain merits special attention.
The 2009 article Possibility of high performance quantum computation by superluminal evanescent photons in living systems reports “Penrose and Hameroff have suggested that microtubules in living systems function as quantum computers by utilizing evanescent photons. On the basis of the theorem that the evanescent photon is a superluminal particle, the possibility of high performance computation in living systems has been studied. From the theoretical analysis, it is shown that the biological brain can achieve large quantum bits computation compared with the conventional processors at room temperature.”
An interesting related topic which I cannot take up here is quantum neural networks, a neural network modeling approach to quantum computing.
Migratory birds most likely use quantum entanglement and superposition for long-distance navigation
Some migratory birds like the European Robin can seasonally fly thousands of miles apparently navigating by sensing changes in inclination the earth’s magnetic field. The angle of such inclination corresponds to latitude. It takes an extremely sensitive detector to do this and quantum entanglement is thought to be a central mechanism for such detection taking place in the eyes of certain birds. In this case the evidence for quantum involvement is a circumstantial one. The 2009 publication Sustained Quantum Coherence and Entanglement in the Avian Compass reports: “In artificial systems, quantum superposition and entanglement typically decay rapidly unless cryogenic temperatures are used. Could life have evolved to exploit such delicate phenomena? Certain migratory birds have the ability to sense very subtle variations in Earth’s magnetic field. Here we apply quantum information theory and the widely accepted “radical pair” model to analyze recent experimental observations of the avian compass. We find that superposition and entanglement are sustained in this living system for at least tens of microseconds, exceeding the durations achieved in the best comparable man-made molecular systems. This conclusion is starkly at variance with the view that life is too “warm and wet” for such quantum phenomena to endure.”
How the radical-pair mechanism works is explained here in a little 2011 article Quantum coherence for birds: “Some migrating birds, such as the European robin, seem to detect the Earth’s magnetic field using light-triggered chemical processes. The idea is that the absorption of a photon excites two electrons on a molecule and that one of these is then passed on to another part of the same molecule, forming a “radical pair”. The pair is produced in a singlet state – but separated in space. The spin of a nucleus in the molecule can couple to one of the electrons and induce singlet-triplet mixing, which is in turn affected by the strength and orientation of an external magnetic field. Subsequent chemical reactions then distinguish between singlet and triplet states, providing information about the magnetic field. — Erik Gauger of the University of Oxford and colleagues studied this phenomenon in light of recent experimental work on the European robin species and found that superposition and entanglement of this spin system are maintained for tens of microseconds or more. — This result is far better than the best similar man-made systems can achieve and it suggests that living things, despite the usual claim that they are too “warm and wet” to maintain coherence for long, could well teach scientists some important tricks for quantum computing.”
The 2010 publication Quantum control and entanglement in a chemical compass reports “The radical-pair mechanism is one of the two main hypotheses to explain the navigability of animals in weak magnetic fields, enabling, e.g., birds to see Earth’s magnetic field. It also plays an essential role in spin chemistry. Here, we show how quantum control can be used to either enhance or reduce the performance of such a chemical compass, providing a new route to further study the radical-pair mechanism and its applications. We study the role of radical-pair entanglement in this mechanism, and demonstrate its intriguing connections with the magnetic-field sensitivity of the compass. Beyond their immediate application to the radical-pair mechanism, these results also demonstrate how state-of-the-art quantum technologies could potentially be used to probe and control biological functions.”
At least one company, QuantumBio, is predicating that the drug discovery process can be facilitated by application of quantum mechanical algorithms. “QuantumBio offers the DivCon Discovery Suite product line, providing solutions to achieve high accuracy, performance, and versatility for chemical characterization in drug discovery and development. The DivCon Discovery Suite is built on cutting-edge technology that utilizes precise quantum mechanical algorithms in a user-friendly format, providing the opportunity for faster results and reduced costs.”
Quantum physics and smell
There is a quantum vibrational theory of smell that is gaining traction(ref). The traditional model for smells is a “key in lock” model where if a molecule fits into a smell receptor then the odor of that molecule is detected. This approach has two serious flaws: first, like-shaped molecules may produce very different smell sensations, and second, an order of magnitude more smells can be detected than there are smell detectors. The quantum theory of smells is that it works by detecting molecules according to their vibrational frequencies where the frequencies are detected by tunneling electrons. The 2007 publication Could Humans Recognize Odor by Phonon Assisted Tunneling? Reports “Our sense of smell relies on sensitive, selective atomic-scale processes that occur when a scent molecule meets specific receptors in the nose. The physical mechanisms of detection are unclear: odorant shape and size are important, but experiment shows them insufficient. One novel proposal suggests receptors are actuated by inelastic electron tunneling from a donor to an acceptor mediated by the odorant, and provides critical discrimination. We test the physical viability of this mechanism using a simple but general model. With parameter values appropriate for biomolecular systems, we find the proposal consistent both with the underlying physics and with observed features of smell. This mechanism suggests a distinct paradigm for selective molecular interactions at receptors (the swipe card model): recognition and actuation involve size and shape, but also exploit other processes.”
Strong empirical evidence for the quantum vibrational model of smell is provided in the discoveries that fruit flies can sniff the difference between chemically identical molecules, one made with ordinary hydrogen, one in which hydrogen is replaced by heavy hydrogen (deuterium)(ref). Fruitflies will be attracted by certain molecules made with ordinary hydrogen but will avoid their heavy hydrogen counterparts. Molecular shape and chemical properties are the same but what is different is vibrational frequency of the molecule. See Molecular vibration-sensing component in Drosophila melanogaster olfaction.
Wrapping it up
· This discussion has been an introduction to quantum biology. There are many additional publications in the area, mostly of a theoretical or modeling nature. Yet my perception is that the field is yet in its infancy, barely getting going.
· We are doubtless quantum beings; our usual chemistry and molecular biology draws on quantum effects. Strange quantum phenomena like tunneling, coherence and entanglement probably affect us profoundly, but mostly in ways we do not fathom yet. Without doubt, these strange quantum effects operate in us despite our scale, warmth and complexity.
· The direct evidence for strange quantum effects in biology is variable so far but is definitely there. In the case of photosynthesis the evidence base is very strong. In the cases of DNA properties, bird navigation neural behavior, and smell the evidence tends to be more circumstantial and theoretical, but it is still quite strong.
· Instead of continuing to ignore the more exotic quantum affects when we study key matters like storage of epigenomic information and gene activation, we are likely in time to find more and more answers to biological puzzles in them.
· Very few people if any have thorough grasps of both biology and quantum physics. They run in different crowds. My impression is that most of the contributions in quantum biology have been made by physicists and mathematicians, often the same people concerned with quantum computing. They know the mathematical language and conceptual frameworks that must be used. Biologists and others trained in the life sciences don’t know them.
· It is a good idea to train a new crop of Ph.Ds in both molecular biology and quantum physics. This will probably come to pass in time.
· Quantum theory as applied to physics raised profound issues with bridge the scientific with the philosophical, issues concerned with the nature of physical reality, issues which persist to today. Likewise quantum biology is raising basic issues. It is sometimes difficult to discern where the boundary is between the scientific and the philosophical. Perhaps there is no such boundary. The question of quantum consciousness has already become such a thought-provoking issue. And who knows, perhaps quantum properties of DNA will confront us with new paradoxes we can’t imagine now.