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Is the Brain a Quantum Computer?

A summary of an argumentative paper by Litt, Eliasmith, Kroon, Weinstein, and Thagard

Consciousness, learning, perception, and memory are mental phenomena that are essential for defining the self and identity. With the rise of quantum computing, theorists have compared explaining mental phenomena to quantum computing in that non-local entanglement and superposition can lead to the possibility for such mental phenomena to exist. However, researchers at the University of Waterloo argue that quantum computing is not essential for explaining mental phenomena like consciousness. Their claim is that mental functions are best explained by neurocomputations rather than quantum mechanics.

Quantum computing is based on the use of so-called qubits (quantum bits). Unlike standard bits, 1s and 0s, of classical computing, qubits can have both 1 and 0 existing simultaneously as the state of a single bit using superposition. The advantage of quantum computing over classical computing is processing speed for certain types of applications. Quantum computing maximizes the optimal processing number of computations per calculation.

It is important to note that a complete understanding of the brain's structure, like a complete understanding of any physical thing, depends on quantum mechanics at the sub-atomic level. However, for explaining brain function, quantum mechanics are irrelevant. The logic gate (specific inputs lead to specific outputs) is the standard operation for classical computing. The timing for a neuron spike firing is relatable to the processing speed of a logic gate rather than a quantum computation. Furthermore, like neuron spikes in the brain, logic gates in classical computations are resistant to static noise. Based on the timing and power required for a neuron spiking, any quantum mechanical instances are considered as noise. The environment of an efficient quantum computer is also drastically contrasted to that of a brain.

There is an important reason for keeping quantum computers in extremely cold environments. In order for qubits to maintain their superposition they must be well isolated from any interference. The lower the temperature, the more isolated the qubits are. The human brain is a warm and wet mass. The brain environment is no where near capable of sustaining isolated qubits. Furthermore, there is the fact that error correction is a real thing that brain neural spiking is capable of. Digital computers are also capable of error correction. Quantum qubits, however, are impossible to correct for error because the superposition would collapse. The natural evolution of the brain is far more efficient for survival than any quantum computing machine. Aside from the computational and the biological arguments, there is also the physiological argument.

It has been theorized that the subconscious precursor process to a conscious thought is the collapse of qubits in microtubules in neurons due to quantum gravitational effects in space-time. These theories have been countered by developments in the continuous understanding of biochemical interactions at the molecular level. It is expected that quantum theories about consciousness will be superseded by the continuation of neurocomputational understanding. While there is no proof against the possibility that quantum mechanics have significant impact on the functionality of the brain, it has been evidenced that the explanation of brain function is far more relatable to classical computation in terms of computational, biological, and physiological arguments.

"Although the discovery of solid evidence for fundamentally quantum characteristics of mental phenomena would be tremendously exciting, current ideas fall well short of this standard." (Litt, Eliasmith, Kroon, Weinstein, and Thagard, 2006)

For further details on the paper, and the arguments against quantum mechanics explaining brain function, please follow the link: Is the Brain a Quantum Computer?