Introduction
The problem of what consciousness is, and how our mind and matter are related to each other are problems that the scientific and philosophical world have always tried to solve. Several
hypothesise have came up with different approaches leading to different or sometimes a common solution. Quantum physics provides us a basic understanding of the microscopic level of the objects and it can provide a conceptual framework for the structural aspects of biological systems and processes via quantum chemistry. In recent years individual biological phenomena such as photosynthesis and bioenergetics have been experimentally and theoretically analysed using quantum methods building conceptual foundations for quantum biology. Since consciousness is attributed to human mind, quantum underpinnings of cognitive processes are a logical extension. This article does not try to formulate a complete quantum description of consciousness or human mind, rather the author tries to present a history of the evolution of the topic and analyse various hypothesises regarding this topic.
Quantum Coherence, Quantum Entanglement, Quantum Wave Function Collapse
For the better understanding of the quantum approaches in biological systems, knowledge
regarding certain terms and ideas of quantum physics are necessary. These are discussed in the following paragraphs. At the end of 20th century Max Plank proposed that energy levels in physical systems can be quantized by the general relation:
En = nhf,
where n enumerates the energy levels and f is the characteristic frequency of internal oscillations. This led to the transformation of physical principles departing from the mechanistic laws of Newtonian physics to provide wave function descriptions of quantum physics. Newton's equations of motion were replaced by the Schrodinger (in the non-relativistic case) and Dirac (in the relativistic case) equations governing the time evolution of the wave functions describing the motion of microscopic objects like elementary particles. Quantum mechanics is a first-quantised theory of physics in which particle properties are discrete but field properties and interactions are not. Quantum field theory is a second-quantized theory in which all particle properties, field properties and interactions are discrete except for those due to gravity. Quantum gravity is an incomplete third-quantized theory during which gravity is additionally made discrete. In physics , objects possess both a wave aspect and a particle aspect. The wave function of a particle describes the probability of finding a particle in a spatial location, thus information about the particle is described probabilistically rather than deterministically. In quantum physics a particle exist in multiple spatial locations and states simultaneously. When a measurement is made, one of the multiple states is chosen and the quantum superposition of states ends being reduced to a classical
state and this process is known as the collapse of the wave function. While quantum mechanics was developed with elementary particles in mind, its subsequent applications extended its validity to systems of many particles. A system of many particles under specific conditions cannot be separated into individual wave functions for each particle, rather it is described by a single wave function describing its collective behaviour. This physical property is called quantum coherence and it is characterized by individual particles losing their separate identities such that the entire system acts as a whole. Decoherence occurs when such a system interacts with its environment in an irreversible thermodynamic way resulting in different particles in the quantum superposition no longer being able to interfere with one another.[1]
Quantum Mechanics At The Synaptic Cleft by Beck and Eccles
Synaptic cleft is a space that separates two neurons and it forms a junction between two or more neurons and helps nerve impulse pass from one neuron to other. Beck and Eccles argued that the process of neutro-transmitter release in the functioning of synapses is governed by the quantum uncertainty principle and involves quantum tunneling, which is a quantum physical phenomenon where a wavefunction can propagate through a possible barrier. They further suggest that the introduction of quantum indeterminacy into neurotransmitter release mechanisms would allow for human free will of action. Their notion is that a quantum process, such as an electron tunneling through an energy barrier, triggers exocytosis, the release of neurotransmitters out of the cell.[2] The sheer size of the vesicle and therefore the sizable amount of neurotransmitter molecules contained in it make it next to impossible to lend itself to quantum tunneling processes. Although the Beck–Eccles model contains very attractive ideas, the crux of the idea appears to be incompatible with the present-day biology of vesicular neurotransmitter release.
Penrose–Hameroff Orchestrated Objective Reduction (Orch OR) Theory
Penrose examined the relationship between consciousness and modern physics and he introduced mathematics as a bridge from the artificial world of computers to the natural world of physics and argued that human consciousness is non-algorithmic, and thus that physical theories of brain function are incomplete due to their dependence on computable algorithmic laws. that quantum effects play a fundamental role in the understanding of human consciousness by enabling the brain to perform non-computable operations. In his explanation of the new physics required to explain the mind and consciousness, he examined the division between classical and quantum physics, specifically the measurement problem, and related the collapse of the wave function to conscious events using the notion of objective reduction. This led to the suggestion that microtubules (long cylindrical structures of cytoskelton) within neurons provide the brain with structures capable of orchestrating the collapse of the wave function via quantum information processing. This union has been known as the Penrose–Hameroff Orchestrated Objective Reduction (Orch OR) theory.[3] The basic idea is that microtubules within the brain's neurons function as quantum computers, with
microtubule protein subunits (tubulins) existing transiently in quantum superposition of two or
more states (i.e., as quantum bits, or “qubits”). According to Orch OR, tubulin qubits in quantum
superposition interact/compute with other superpositioned tubulins in microtubule lattices by
nonlocal quantum entanglement, eventually reducing (“collapsing”) to particular classical tubulin states after 25 milliseconds or so. The quantum state reductions yield conscious perceptions and volitional choices, which then govern neuronal actions. The central postulate of the Orch OR theory is that the site of action of consciousness is located within the brain's microtubules which operate at the interface between classical neurophysiology and quantum gravitational forces. These claims have found both ardent supporters and vocal critics
in the scientific community. The most influential criticism was raised by Tegmark. He estimated the decoherence time of tubuline superpositions due to interactions in the brain to be less than 10-12sec. Compared to typical time scale of tubuline processes of the order of milliseconds or more, he concluded that the lifetime of superposition of tubuline is much too short to be significant neurophysiological processes in the microtubuli.[4] But later it was shown that the corrected version of Tigmark’s model provides decoherence time upto 10 to 100 microseconds and it has been argued that this can be extended upto the neurophysiologically relevant range of 10 to 100msec under particular assumptions of the scenario by Hameroff and Penrose.
Conclusion
Exploring quantum physics for understanding the basic framework of conscousness can be an
exciting journey. Each of the hypothesis discussed above has both promising and problematic
aspects. The approach by Beck and Eccles applying Standard Quantum mechanics to excytosis is detailed and concrete but does not solve the problem of how the activity of single synapses enters the dynamics of neural assemblies. The work by Penrose and Hameroff is the most promising one which exceed the domain of present day Quantum theory.
We foresee major progress in bridging the gap between nanoscience and consciousness in the area of nano-neuroscience where MT's, actin filaments and motor proteins connect between
neurophysiology and molecular biology. Studying the neural phenomena at a nanoscale will lead to monumental breakthroughs in science and medicine and aid in consciousness studies. Further possibilities involving physically-based quantum mechanisms of consciousness should also be considered.
References
Stuart R. Hameroff, Travis J. A. Craddock, Jack A. Tuszynski, Quantum effects in the understanding of consciousness, Journal of Integrative Neuroscience
Beck, F. & Eccles, J.C. (1992) Quantum aspects of brain activity and the role of consciousness, Proc. Natl. Acad. Sci. USA
Hameroff.S, Penrose.R , Orchestrated reduction of quantum coherence in brain microtubules: A model for consciousness, Mathematics and Computers in Simulation 40 (1996) 453-480
Tegmark, M. (2000) Importance of quantum coherence in brain processes. Phys. Rev.
By Goutham Gopal K.V
gouthamgopal03@gmail.com
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