In my guest blog for Scientific American, I wrote about the work of Bob Coecke who has designed a graphical mathematics, based on a branch of mathematics called category theory. He uses this diagrammatic calculus to describe and investigate quantum mechanical processes. Coecke’s work has found application in biology and linguistics, suggesting some interesting links between mathematics, physics and biology. But yet another link between quantum mechanics and biology is discussed in a recent article on the Foundational Questions Institute website: Could quantum effects explain the mechanisms behind smell, photosynthesis and bird navigation?
In the article Carinne Piekema reviews the work of three researchers – quantum physicists Simon Benjamin at Oxford University and Alex Chin at the University of Cambridge, and biophysicist Luca Turin. Turin was one of the first to suggest a quantum effect in a biological process, namely, in how we distinguish odors. This description of biological receptors sets up the problem Turin’s work addresses.
In general, for biological receptors, shape is everything. Molecules of a certain shape are able to bind with particular receptors, triggering them via what’s known as the “lock-and-key” mechanism. This is true for antibodies, hormones, enzymes and even many neurotransmitters, so it seems perfectly reasonable to assume that molecules with similar shapes would bind to the same receptors in the nose, generating identical smell sensations. Indeed, this idea forms the basis of the conventional, non-quantum theory of smell.
But, Turin explains, “There doesn’t seem to be a correlation between molecular structure and its smell.” Recognizing this fact led Turin to propose that we distinguish smells on the basis of the frequencies with which their bonds vibrate, rather than on their shape. But a quantum mechanical process is needed to explain how that kind of interaction can happen within the nanoscale of proteins in your nose. The experimental verification of this idea has run into some difficulties, but Turin has remedied some of them and is optimistic and encouraged by a related investigation of photosynthesis, an extremely efficient process that works even in the low light conditions of the ocean bottom.
The extreme efficiency seems surprising given that the signal needs to travel all the way down the leaf, to its “reaction centre,” which in itself costs energy. In 2007, chemist Greg Engel, then at the University of California, Berkeley, and colleagues ran a series of experiments that suggested that the process might actually make use of a quantum property known as superposition—the ability to be in two or more places at the same time. “When people were able to zoom in on what was happening in these tiny time windows, they saw that actually energy doesn’t just hop from molecule to molecule,” explains Chin. “It actually spreads in a wave-like manner, thus evolving according to the laws of quantum mechanics.”
But I most enjoyed the discussion of bird navigation. Based on the observation that vision plays a role in the European robin’s sense of direction, Benjamin and colleagues have come up with a hypothesis to describe the quantum mechanical processes involved in the birds’ sense of the earth’s magnetic field:
The quantum physicists now believe that the bird might actually “see” a grid like pattern on its eyeballs. The idea is that when a molecule in the eye absorbs a photon from sun light, it gives an energetic nudge to a pair of electrons in the molecule. The electrons are entangled—that is, they are inextricably linked by a quantum property so that they influence each other, no matter how far apart they are separated. One of the electrons in the pair is dislodged and kicked off to a new location, but it remains linked to its partner, and each feels a slightly different level of magnetism, due to the Earth’s field. Before the transported electron relaxes back to its original state, a small electric dipole field is created, leaving a little trace on the bird’s vision. The orientation of the molecule with respect to the Earth’s magnetic field dictates how quickly the electron relaxes back and thus controls the strength of the superimposed image on the bird’s vision. The orientation of the molecule with respect to the Earth’s magnetic field dictates how quickly the electron relaxes back and thus controls the strength of the superimposed image on the bird’s vision.
What I find most interesting about these reports is the way that the unshakeable presence of quantum mechanics in physics seems to be prying open conceptual structures, or newly imagined views of the living material that is the subject of biology. Despite the fact that we call it quantum ‘mechanics,’ quantum theory shattered the mechanical world view that prevailed in classical physics. But that classical world view continues to have some general influence. The conceptual shift in the research discussed here is not fully clarified. But it does look like the mind’s eye is getting nudged a bit, and beginning to see that there are many things that may happen in ways we have not yet imagined. This kind of thinking will undoubtedly refresh our sense of what is real.
Recent Comments