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Friday, 18 January 2019

Quantum Computing, Capabilities and Limits

https://gigaom.com/2019/01/17/quantum-computing-capabilities-and-limits-an-interview-with-scott-aaronson/

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 it’s been argued by some that human consciousness is itself a quantum phenomenon. Does that mean anything to you?
It’s an interesting hypothesis, but I don’t think there’s good evidence at this time for consciousness involving quantum computation, and there are several difficulties that any theory of that kind would have to overcome. The first one is that the brain seems like an incredibly hot and wet and noisy environment. It seems like no place for a qubit.
But the answer to that has been that they do believe now that quantum phenomena are occurring like in a bird’s navigation systems and things like that.
Oh yeah, that’s right, there is no question that there are quantum effects that are important for biology, that is not in dispute for bird navigation.  Also green plant photosynthesis is a quantum effect, but maybe this is not so surprising, because all of chemistry is based on quantum mechanics right? So of course when you go to a small enough scale, you’re going to see quantum phenomena. What’s cool is that evolution was sometimes able to exploit these phenomena, but now the problem is if you want [to see a] human thought display, the brain is a very large system. This is not on the molecular scale, and once things are resolved to the level of a given neuron is inspiring a signal, across an axon or it’s not firing one, right, then that seems like very much a classical event. It’s an event that leaves records in its environment, that’s what I mean by that.
But to jump in on that one for just a second, but within the neuron itself, I mean we don’t know how a neuron does what it does, it could be operating at the Planck level, right?
The problem is that a neuron does not have anything of a nearly high enough energy to probe physics at the Planck scale. Not even the Large Hadron Collider is able to get anywhere near to Planck scale. This is 20 orders of magnitude bigger than the Planck scale, then yeah it is not ruled out.  There could be all sorts of weird quantum phenomena taking place in a neuron, but then one would then have the burden of showing that any of those phenomena were important for consciousness, as opposed to just being like another source of thermal noise, effectively. So that’s where that discussion is. If you want us to have a quantum account of consciousness, I think that there are further difficulties. The first thing is you have to have a reason why is that [needed], what does that help you to explain that was previously unexplained?
The answer to that might be along the lines of, there seem to be sorts of problems that the human brain can solve that don’t seem to be solvable by a Turing machine.
I’m not sure that that’s true actually. Now I would say we don’t know the answer to that. I mean the famous ‘halting problem’ that proveably no Turing machine is able to solve, but I can’t solve the halting problem either. If I could then I could immediately win the field medal in Math by resolving thousands of famous unsolved math problems. I try to solve math problems, but it’s very much hit or miss, so what we know from the work of Godel and Turing and those people is that you could never build a computer and some people have seized on that point.
Some people like Roger Penrose have seized on the observation by Godel and Turing that no machine can be a perfect oracle for mathematics. In order to say that the brain or at least the mathematician’s brain must be doing something that a Turing machine can’t, but the obvious problem with that argument is that humans are not perfect oracles for mathematics either to put it very mildly. To achieve the dreams of AI, a computer would not need to be a perfect mathematician, it would merely have to be as smart as or smarter than us.

....  a blog about quantum computing and also all sorts of other things, that’s www.scottaaronson.com/blog ...

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