(P2/2)

I don’t think this is the case. As far as I know a human brain consists of neurons which roughly either fire or don’t fire. That’s a bit like a 0 or 1. But that’s an oversimplification and not really true. But a human brain is closer to that than to an analog computer. And it certainly doesn’t use quantum effects. Yes, that has been proposed, but I think it’s mysticism and esoterica. Some people want to hide God in there and like to believe there is something mystic and special to sentience. But that’s not backed by science. Quantum effects have long collapsed at the scale of a brain cell.[...]

The skepticism about quantum effects in the brain is well-founded and represents the orthodox view. The "brain is a classical computer" model has driven most of our progress in neuroscience and AI. The strongest argument against a "quantum brain" is of decoherence. In a warm wet brain quantum coherence is rapid. However, quantum biology doesn't require brain-wide, long-lived coherence. It investigates how biological systems exploit quantum effects on short timescales and in specific, protected environments.

We already have proven examples of this. In plant cells, energy transfer in photosynthetic complexes appears to use quantum coherence to find the most efficient path with near-100% efficiency, happening in a warm, wet, and noisy cellular environment. Its now proven that some enzymes use quantum tunneling to accelerate chemical reactions crucial for life. The leading hypothesis for how birds navigate using Earth's magnetic field involves a quantum effect in a protein called cryptochrome in their eyes, where electron spins in a radical pair mechanism are sensitive to magnetic fields.

The claim isn't that a neuron is a qubit, but that specific molecular machinery within neurons could utilize quantum principles to enhance their function.

You correctly note that the "neuron as a binary switch" is an oversimplification. The reality is far more interesting. A neuron's decision to fire integrates thousands of analog inputs, is modulated by neurotransmitters, and is exquisitely sensitive to the precise timing of incoming signals. This system operates in a regime that is often chaotic. In a classically chaotic system, infinitesimally small differences in initial conditions lead to vastly different outcomes. The brain, with its trillions of interconnected, non-linear neurons, is likely such a system.

Consider the scale of synaptic vesicle release, the event of neurotransmitter release triggered by the influx of a few thousand calcium ions. At this scale, the line between classical and quantum statistics blurs. The precise timing of a vesicle release could be influenced by quantum-level noise. Through chaotic amplification, a single quantum-scale event like the tunneling of a single calcium ion or a quantum fluctuation influencing a neurotransmitter molecule could, in theory, be amplified to alter the timing of a neuron's firing. This wouldn't require sustained coherence; it would leverage the brain's chaotic dynamics to sample from a quantum probability distribution and amplify one possible outcome to the macroscopic level.

Classical computers use pseudo-random number generators with limited ability to truly choose between multiple possible states. A system that can sample from genuine quantum randomness has a potential advantage. If a decision process in the brain (like at the level of synaptic plasticity or neurotransmitter release)is sensitive to quantum events, then its output is not the result of a deterministic algorithm alone. It incorporates irreducible quantum randomness, which itself has roots in computational undecidability. This could provide a physical basis for the probabilistic, creative, and often unpredictable nature of thought. It's about a biological mechanism for generating true novelty, and breaking out of deterministic periodic loops. These properties are a hallmark of human creativity and problem-solving.

To be clear, I'm not claiming the brain is primarily a quantum computer, or that complexity doesn't matter. It absolutely does. The sheer scale and recursive plasticity of the human brain are undoubtedly the primary sources of its power. However, the proposal is that the brain is a hybrid system. It has a massive, classical, complex neural network as its substrate, operating in a chaotic, sensitive regime. At the finest scales of its functional units such as synaptic vesicles or ion channels, it may leverage quantum effects to inject genuine undecidably complex randomness to stimulate new exploration paths and optimize certain processes, as we see elsewhere in biology.

I acknowledge there's currently no direct experimental evidence for quantum effects in neural computation, and testing these hypotheses presents extraordinary challenges. But this isn't "hiding God in the gaps." It's a hypothesis grounded in the demonstrated principles of quantum biology and chaos theory. It suggests that the difference between classical neural networks and biological cognition might not just be one of scale, but also one of substrate and mechanism, where a classically complex system is subtly but fundamentally guided by the unique properties of the quantum world from which it emerged.