Paul Davies – living organims

As a physicist, Paul Davies, starts by noting that living organisms represent a state of matter in a class apart from all other matter. The cell is the basic subunit of living matter, and is now understood to be full of nanomachines in the form of the organelles, cytoskeleton, receptors and synapses. Davies discusses Heisenberg’s uncertainty principle as a possible objection to quantum involvement in brain processes. Uncertainty is a potential problem for living organisms, because replication requires the accurate coordination of molecules. Uncertainty principle is usually explained in terms of not being able to know both the exact position and exact momentum of a quantum particle. The more one knows about one, the less one can know about the other. However, the same constraint applies to other aspects of a quantum particle, such as time and energy. Time uncertainty represents a problem with respect to living organisms, because the uncertainty compromises the accuracy of timing that is vital to life, which depends on the timely organisation of molecules for replication and other processes.

In fact, it is possible to calculate the minimum size of a clock of a given accuracy. This calculation derives from the physicist, Eugene Wigner, in the 1950s. Wigner’s calculation has thrown up some interesting correlations in terms of various organisms, in circumstances where these can be regarded as clocks. For mycoplasma cells, it is possible to calculate a reliability time limit of about an hour for internal time keeping. It now transpires that their reproductive cycle also takes an hour. The internal components of the cell are much smaller than the cell itself and have a correspondingly shorter period of accurate time keeping, but despite this similar instances arise at the cellular coponent level. Thus the polymerase enzyme that moves along the unzipped strands of DNA covers a bit over 100 base pairs per second, which is in line with the minimum speed required to retain accuracy of timekeeping at the quantum level. Protein folding times have also been shown to be close to the limit allowed if accuracy of quantum time keeping is to be retained.

It is also suggested that quantum mechanics may play a more positive role in organisms. Apoorva Patel at the Indian Institute of Science proposes that quantum mechanics could be involved in speeding up the process by which polymerase finds bases to bind to the DNA strand. It is suggested that this could involve an application of Grover’s algorithm, an algorithm that manmade quantum computers might eventually use to search massive and jumbled databases. The DNA strand has four bases, three letters of this strand at a time code for the amino acids, and there are 20 amino acids. Biologists have often speculated about the apparently arbitrary nature of these numbers. Patel points out that 3, 4 and 20 would emerge naturally from the application of Grover’s algorithm.

Genetic mutation has often been suggested to be the result of quantum fluctuations. Jonjoe McFadden and Jim Al-Khalili at Surrey University suggested that the ability of bacteria to respond to shortage of nutrients might have a quantum origin.

A final suggestion is that quantum processes might have been involved in the origin of life on Earth. The odds against a replicator emerging from a soup of molecules are usually calculated to be very high, and some form of quantum search, making use of Grover’s algorithm could have facilitated the emergence of the first replicators. If quantum processes were involved in the origin of life, it is likely that they would have been retained as organisms evolved.

At the end of his paper, Davies discusses the extent to which decoherence is a problem for quantum processes in biological tissue. He agrees that a simple model shows that decoherence in biological tissue will happen much too quickly for quantum processes to be biologically useful. However, he points out that simple models often fail to take account of all the relevant features in real systems. For instance, in some situations, decoherence does not proceed at a uniform rate, but the collapse of part of a system to the classical level creates conditions that protect the quantum coherence of the remainder of the system.

Davies further reminds us that it was Schrödinger’s 1944 book ‘What if Life?’ that inspired Crick to study DNA. Schrödinger had correctly guessed that genetic information was encoded in large molecules. What has now been air brushed from mainstream scientific history is that he and others expected living organisms to prove to be fundamentally quantum.
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