Masayuki Hirafuji
Computational modeling Laboratory, National Agriculture Research Center, Tsukuba, 305-8666 Japan
Proposals that quantum effects may be related to macroscopic functions such as consciousness are often countered with the suggestion that quantum coherence is destroyed by thermal noise at room temperature. Here we propose two possible universal mechanisms which might generate quantum effects only in such vastly complex systems.
The first mechanism, common to enormously complex systems, consists in the ability to sense very weak signals in the presence of strong noise. Here we assume the complex system to be comprised of a very large number of components such as protein molecules, organelles and cells. Input to and output from the components differ according to site and substance. In neural networks, they are given by the intensity of impulses; in membrane systems, by the electric potential or electric field; in bio-molecular systems, by the intermolecular interactions. There are both weak and strong bi-directional and nonlinear interactions among components; that is, the components form a fully interconnected network. In a system in which the total influence (input) on a component is the weighted sum of influences coming from all other components, noise from other components is offset while weak signals from weakly-connected components are added. For a vast collection of components, noise can be made very weak and the total signal strong. The reaction of components to a signal is primarily nonlinear. In this case moderate noise assists components in sensing weak signals through the mechanism of stochastic resonance. Together, the group of components is able to extract weak signals. Moreover there exists a critical number of components to perform this function. A huge collection having enough components can thus be strongly ordered by only very weak signals otherwise hidden by noise.
SNR (Signal / Noise Ratio) in the system increases as O(n^3/2), where n is the number of components. For example, if n is 10^8 then SNR increases to 10^12. The threshold signal in the presence of thermal noise (40x10^-22J) is about 10^-34 J, of the same order as the Planck constant. By this mechanism, biological systems, such as supramolecular complexes in cells, ion channels in membranes, and neural networks have the potential to create order from weak signals originating in quantum effects.
Biological systems have a hierarchical structure. The state of microscopic systems, such as molecules or molecular aggregates (ion channels in membranes), affects the state of systems more macroscopic. But the reaction from macroscopic to microscopic levels is weak, because macroscopic systems cannot individuate objects on a microscopic scale. Here we assume that the reaction from macroscopic levels consists solely in noise and that microscopic systems have multiple states, transitions between which are caused by quantum tunneling. The tunneling probability is increased by the addition of noise, since the barrier between stable states then fluctuates. This quantum-macroscopic complex system searches for the point of least noise as there the tunneling probability becomes minimal. By this mechanism, macroscopic quantum effects appear in biological systems, performing a global search function.