Human brain, Turing machines and quantum computers

(In this post I am archiving discussion on Reddit.)

What do you think about hypothesis that human brain cannot be simulated in Turing machine (modern digital computer) because human brain is more like quantum computer (utilize quantum mechanic effects to function)?

Maybe quantum effects can be emulated on modern digital computer (Turing machine) but speed of this simulation will be absurdly slow.

Maybe we should use quantum computers when trying to simulate quantum brain?

If such a "noisy" and hot environment as the human brain could use quantum computation, then why are we having such a hard time designing quantum computers in the lab? It is fairly obvious that you need to invoke some kind of magic if you want to claim that quantum computing takes place in the brain. Unless something very magical happens, decoherence will surely kill any quantum computational effects, see http://arxiv.org/abs/quantph/9907009.hopffiber

So, maybe human brain is like modern digital computers - they are made of quantum objects but their designers (I am not implying that human brain is made by "intelligent designer") made precautions to make computers to work predictable (without quantum uncertainty).

The modern computers are proof of concept that there is possible to be build non-quantum computers with quantum objects.

(Sometimes hard drives and other components fail, but this is rare event. Nothing is perfect.)

However, I suppose that natural brains are more unpredictable than modern computers - a very small changes (because of quantum effects) may lead to a very different output. Modern computers are protected (they can receive only 0 and 1), but natural brains may receive single photons and react on them!

http://www.preposterousuniverse.com/blog/2013/04/12/frogs-see-photons/

http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html

http://en.wikipedia.org/wiki/Absolute_threshold

The human eye is very sensitive but can we see a single photon? The answer is that the sensors in the retina can respond to a single photon. However, neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms. If we could consciously see single photons we would experience too much visual "noise" in very low light, so this filter is a necessary adaptation, not a weakness.

Sure, comparing to modern computers is better, its just not quantum computing since it doesn't use superpositions to do calculation. I think most things that happens in the brain is well described by classical physics even if the things interacting are small and "quantum".

Also, I think the analogy about "reacting to a single photon" is misleading: its not the brain itself that reacts to a single photon, but rather a cell in the eye. The eye is a photo sensor, reacting to the photon and sending on a magnified signal to the brain; you should compare it to a computer being connected to a camera, and we can surely connect a computer to a camera able to sense individual photons. The brain being unpredictable is rather because its a very, very complicated thing, and we don't know all that much still about how it works.
hopffiber

However, neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms.

So, if the brain would not react on (for example) 9 photons (within less than 100 ms), but it will react on 10 photons (within less than 100 ms), we can place a "9 photons per 100 ms" generator to simulate "single photon sensitive brain".

I am also thinking of some other way quantum effects may interfere with human brain.

Quantum effects within the neurons can be amplified to macro level (because the brain's "noise protection" is not perfect as corresponding in modern computers). I know how modern computers work (how their noise protection works). But I don't understand the brain's noise protection.

I am not sure that this cannot be utilized in some sort of "quantum network" effect because I am not sure how the collapse of the quantum wave function actually works.

it doesn't use superpositions to do calculation

This is valid for one neuron. But is this valid for entire brain?


I don't know about the "noise protection" of the human brain either, but I find it hard to believe that quantum randomness on a particle level can propagate very much. The decoherence times are just too short, way shorter than the timescales for neuron communication. But I'm not an expert and maybe there is some chaotic behavior that can amplify even the tiniest differences.

This is valid for one neuron. But is this valid for entire brain?

Yes, since decoherence will kill all superpositions; especially for a large system as the whole brain. If you read the people who suggested that quantum computation has anything to do with how we think, they think that the quantum computation takes place in a small part of individual neurons, the microtubules. hopffiber


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What do you think about hypothesis that human brain cannot be simulated in Turing machine (modern digital computer) because human brain is more like quantum computer (utilize quantum mechanic effects to function)?

Maybe quantum effects can be emulated on modern digital computer (Turing machine) but speed of this simulation will be absurdly slow.

Maybe we should use quantum computers when trying to simulate quantum brain?


Unfortunately, people who use the word "quantum" in the context of brain and intelligence are really using it as a synonym for "magic", and don't understand what quantum effects are. There is nothing about our brains that implies quantum effects are significant, for the simple reason that our brains are clearly a huge number of interconnected neurons. Neuroscientists can see signals going from neuron to neuron. Where in all this discrete signalling would quantum computing be hiding?

The fundamental difference between brains and Turing machines is that the brain is massively parallel. That has enough explanatory power for the brain, even if we don't completely understand the exact particulars. We don't need to drag in quantum mechanics.nairebis

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