Quantum mind theories are based on the premise that quantum theory is necessary to fully understand the mind and brain, particularly concerning an explanation of consciousness. Introduction The quantum mind hypothesis proposes that classical mechanics cannot fully explain consciousness and suggests that quantum mechanical phenomena such as quantum entanglement and superposition may play an important part in the brain’s function and could form the basis of an explanation of consciousness. Supporters of the quantum mind hypothesis have not submitted any evidence to support its claims for peer review, but the hypothesis has also not been falsified. Motivation Consciousness Banished A common argument underlying the quantum mind thesis is that classical mechanics cannot explain consciousness, if only because Galileo and Newton excluded the secondary qualities from the physical world. Fritjof Capra writes: To make it possible for scientists to describe nature mathematically, Galileo postulated that they should restrict themselves to studying the essential properties of material bodies – shapes, numbers, and movement – which could be measured and quantified. Other properties, like color, sound, taste, or smell, were merely subjective mental projections which should be excluded from the domain of science. Proponents of the Quantum mind state that qualities such as sound, taste and smell are an essential part of the human experience and therefore cannot be discounted. They believe that classical mechanics fails to account for the experience of such phenomena. Similarly, they believe that the internal experiences of consciousness, such as dreaming and memory, all of which are ‘part and parcel’ of everyday human experienced remain unaccounted for. Minimization of Mystery The philosopher David Chalmers half-jokingly claims that the motivation for Quantum Mind theories is: “a Law of Minimization of Mystery: consciousness is mysterious and quantum mechanics is mysterious, so maybe the two mysteries have a common source.” Ongoing Debate Science The main argument against the quantum mind proposition is that the structures of the brain are much too large for quantum effects to be important. It is impossible for coherent quantum states to form for very long in the brain and impossible for them to exist at scales on the order of the size of neurons. This does not imply that classical mechanics can explain consciousness, but that quantum effects including superposition and entanglement are insignificant. Quantum chemistry is required to understand the actions of neurotransmitters, for example. One well-known critic of the quantum mind is Max Tegmark. Based on his calculations, Tegmark concluded that quantum systems in the brain decohere quickly and cannot control brain function, “This conclusion disagrees with suggestions by Penrose and others that the brain acts as a quantum computer, and that quantum coherence is related to consciousness in a fundamental way”. Philosophy Another line of criticism is that no physical theory is well suited to explaining consciousness, particularly in its most problematical form, phenomenal consciousness or qualia, known as the hard problem of consciousness. It is not so much that colours and tastes and feelings –qualia or secondary qualities — have been deliberately banished, but more that they cannot be captured in any mathematical description, which means they cannot be explicitly represented in physics, since all physical theory is expressed in mathematical language . If no physical theory can express qualia, no physical theory can fully explain consciousness. Replacing the mathematical apparatus of classical physics with the mathematical apparatus of quantum mechanics is therefore of no help in understanding consciousness, and indeed there is no known example of a quantum equation which encapsulates a taste or colour. As David Chalmers puts it: Nevertheless, quantum theories of consciousness suffer from the same difficulties as neural or computational theories. Quantum phenomena have some remarkable functional properties, such as nondeterminism and nonlocality. It is natural to speculate that these properties may play some role in the explanation of cognitive functions, such as random choice and the integration of information, and this hypothesis cannot be ruled out a priori. But when it comes to the explanation of experience, quantum processes are in the same boat as any other. The question of why these processes should give rise to experience is entirely unanswered. Other philosophers, reject the idea that there is anything puzzling about consciousness in the first place.