I’ve become more and more interested in the macroscopic manifestations of quantum effects. Partly because I am thinking about the where we should properly place the boundary between the classical regime and the quantum regime, and what implications that scientific decision might have on the ways we do theology. (Remember that at my heart I’m a post-positivist. As such the question of how closely we can approach the truth is really quite important.)

I linked a while ago to reports about how researchers have extended the observed range of quantum correlations from the size of the typical bucky ball to now micrometer sized objects composed of trillions of atoms. When I taught physics I regularly pointed out that despite our tendency to think we can ignore quantum effects at the macroscopic level, simple electronic devices based on the transistors would be impossible without such effects. And now there is a paper that explains a common conundrum on biophysics by making use of a quantum state analysis. (Which will lead to some of the attendant weirdness of quantum physics when the model is extended or more fully developed.)

“Tieyan Si at the Max Planck Institute for Complex Systems in Dresden, Germany, has created a quantum model of muscle behaviour. His idea is that myosin, the molecular motor responsible for muscle contraction, is essentially a quantum object and that its behaviour is best described by quantum mechanics.

The business part of muscle fibre consists of actin, which can be thought of as a rope, and myosin, which is a molecular motor which works rather like a tug-of-war team. Electrical stimulation sets the tug of war teams into action, frantically pulling their ropes and causing the muscle to contract. The actual force a muscle produces is the result of many myosin motors pulling and relaxing, although not necessarily in concert.

The challenge for theorists is to work out how these molecular motors generate the force and relaxation curves that occur in real muscle. These are well studied in systems as diverse as mammalian heart muscle and insect wings and biomechanicists have long known that different types of muscle and muscle action produce different force curves. For example, contractions that are quickly released have a different force signature to slowly release ones. Explaining this with a single classical theory is not easy.

Si’s approach is simply to assume that each myosin motor is a quantum object that can form two shapes and that the switch between these shapes causes a contraction. In other words, it has two states. (He also looks at a system in which myosin has three states.) Myosin switches to one state by absorbing energy and relaxes by emitting it and the combined effect of all the switchings determine the behaviour of the fibre.

A muscle fibre, then, is simply a chain of these quantum objects, for which it is possible to derive a mathematical object known as a Hamiltonian that describes the behaviour. The question that Si addresses is that what kind of force-relaxation curves does this Hamiltonian lead to.”

Read the full article here.