# Not quantum

Quantum computers are Turing-equivalent, so even if the brain was a quantum computer, all of its algorithms would still be computable on classical computers.

• But quantum computers are much faster for certain problems; Quantum supremacy
• Shor's algorithm for factoring integers is exponentially faster than best classical algorithms
• So if the brain exploits a quantum algorithm with no efficient classical alternative, standard computers will be unable to run AGI efficiently

The brain is almost certainly not a quantum computer.1

• Quantum computers require environments isolated from vibration and other external influences to prevent decoherence from erasing the state information.
• Although the brain has some cushioning, it’s not nearly enough
• Quantum phenomena operate on timescales of $$10^{-13}$$ seconds, but neuron spiking frequencies are on the order of $$10^{-3}$$ seconds.
• i.e. brain is quantum computer implies that neuron spikes cannot be involved in processing
• The temperature in the brain is probably too high for stable quantum computation

So the brain’s algorithms will run on classical computers without exponential slowdown.*

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1. Litt, A., Eliasmith, C., Kroon, F.W., Weinstein, S. and Thagard, P. (2006), Is the Brain a Quantum Computer?. Cognitive Science, 30: 593-603 ↩︎