Who thinks quantum computing will be necessary for AI?

To me it seems straightforward: Intelligence is magical. Classical computers are not magical. Quantum computing is magical. Therefore we need quantum computing for AI.

However, if after a few years quantum computing becomes non-magical, it will become obvious that we need something else.

Why would QC be relevant? What quantum effects does the brain exploit? Or what classical algorithms which are key to AI tasks would benefit so enormously from running on a genuine quantum computer (as opposed to a quantum or quantum-inspired algorithm running on a classical computer) that they would make the difference between AI being possible and impossible?

No serious neurologists actually consider quantum effects inside microtubules or arrangements of phosporyulation on microtubules or whatever important for neuron function. They're all either physicists who don't understand the biology or computer scientists who don't understand the biology. Nothing happens in neural activity or long-term-potentiation or other processes that cannot be accounted for by chemical processes, even if we don't understand exactly the how of some of them. The open questions are mostly exactly how neurons are able to change their excitability and structure over time and how they manage to communicate in large scale systems.

There's an overview of the "quantum mind" debate among academics (whether quantum effects play an important role in the function of the brain) in FHI's Whole Brain Emulation Roadmap (page 37). This isn't quite the same question you're asking (since even if the brain uses quantum computing, an AI may be able to avoid it through some kind of algorithmic workaround), but I'd guess that most supporters of the "quantum mind" hypotheses would also answer "yes" to your question.

I don't think that most (perhaps not all) people who say such things (QC is necessary for AI) understand both what building blocks might be needed for AI and what quantum computers actually can and can't do better or worse than classical computers. Sounds like people throwing two awesome (but so far impractical) concepts they've heard about together randomly, hoping for an even more awesome statement. Like "for colonizing Mars it's necessary that we build room-temperature superconductors first".

Please excuse the ridicule, but I don't see how large quantum computers are necessary for AI. They certainly are helpful, but then, room-temperature superconductors also are...

Anything a quantum computer can do, a classical computer can do, if slower.

Who thinks quantum computing will be necessary for AI?

David Pearce for one:

The theory presented predicts that digital computers - and all inorganic robots with a classical computational architecture - will 1) never be able efficiently to perform complex real-world tasks that require that the binding problem be solved; and 2) never be interestingly conscious since they are endowed with no unity of consciousness beyond their constituent microqualia - here hypothesized to be the stuff of the world as described by the field-theoretic formalism of physics.

Quantum computers can be simulated on classical computers with exponential slow down. So even if you think the human mind uses quantum computation, this doesn't mean that the same thing can't be done on a classical machine. Note also that BQP (the set of efficiently computable problems by a quantum computer) is believed (although not proven) to not contain any NP complete problems.

Note also that at a purely practical level, since quantum computers can do a lot of things better than classical computers and our certainty about their strength is much lower, trying to run an AI on a quantum computer is a really bad idea if you take the threat of AI going FOOM seriously.

These people's objections are not entirely unfounded. It's true that there is little evidence the brain exploits QM effects (which is not to say that it is completely certain it does not). However, if you try to pencil in real numbers for the hardware requirements for a whole brain emulation, they are quite absurd. Assumptions differ, but it is possible that to build a computational system with sufficient nodes to emulate all 100 trillion synapses would cost hundreds of billions to over a trillion dollars if you had to use today's hardware to do it.

The point is : you can simplify people's arguments to "I'm not worried about the imminent existence of AI because we cannot build the hardware to run one". The fact that a detail about their argument is wrong doesn't change the conclusion.

In principle, it should be quite possible to map a human brain, replace each neuron with a chip, and have a human-level AI. Such a design would not have the long-term adaptability of the human brain, but it'd pass a Turing test trivially. Obviously, the cost involved is prohibitive, but it should be a sufficient boundary case to show that QC is not strictly necessary. It may still be helpful, but I'm sufficiently skeptical of the viability of commercialized QC to believe that the first "real" AI will be built from silicon.

I don't think we'll need quantum computing specifically for AI.

I do think that it's possible, though, that we might need to make significant improvements in hardware before we can run anything like a human-level AI.

I begin to think that we should taboo the words "AI" and "intelligence" when talking about these subjects. It's not obvious to me that, for example, whole brain emulation and automated game playing have much in common at all. There are other forms of "AI" as well. Consequently we seem to be talking past each other as often as not.

There are a lot of things we simply don't know about the brain, and even less so about consciousness and intelligence in the human sense. In many ways, I don't think we even have the right words to talk about this. Last I checked scientists were not sure that neurons were the right level at which to understand how our brains think. That is, neurons have microtubule substructures several orders of magnitude smaller than the neurons themselves that may (or may not) have something significant to do with the encoding and processing of information in the brain. Thus it's conceivable that a whole-brain emulation at the level of individual neurons might be insufficient to produce human-type intelligence and consciousness. If so, we'd need quite a few more generations of Moore's law before we could expect to finish a whole brain emulation than we're currently estimating.

Furthermore the smaller structures would be more susceptible to quantum effects. Then again, maybe not. Roger Penrose and Stuart Hameroff have developed this as Orchestrated objective reduction theory. This theory has been hotly disputed; but so far I don't think it's been conclusively proven or disproven. However, it is experimentally testable and falsifiable. I suspect it's too early to claim definitively either that quantum effects either are or are not required for human type intelligence and consciousness; but more research will likely help us answer this question one way or the other.

I will say this: there is a lot of bad physics and philosophy out there that has been misled by bad popular descriptions of quantum mechanics and how the conscious observer collapses the wave function, and thus came to the conclusion that consciousness is intimately tied up with quantum mechanics. I feel safe ruling that much out. However it still seems possible that our consciousness and intelligence is routinely or occasionally susceptible to quantum randomness, depending on the scale at which it operates.

Even if Penrose's ideas about how human intelligence arises from quantum effects is all true, that still does not prove that all intelligence requires quantum randomness. If you want to answer that question, then the first thing you need to do is define what you mean by "intelligence". That's trickier than it sounds at first, but I think it can be usefully done. In fact, there are multiple possible definitions of intelligence useful for different purposes. For instance one is the ability to formulate plans that enable one to achieve a goal. Consciousness is a much thornier nut to crack. I don't know that anyone has a good handle on that yet.

There will be AI long before there are quantum computers.

At the very least, I'm relatively certain that quantum computing will be necessary for emulations. It's difficult to say with AI because we have no idea what their cognitive load is like, considering we have very little information on how to create intelligence from scratch yet.

There is no evidence that the speedup by quantum computing is necessary for the emergence of intelligence. As far as we can tell, quantum phenomena are not especially involved in our cognitive architecture - despite Penrose's protestations to the contrary -, no more than they are involved in our normal PCs.

Now what does E-v-i-d-e-n-c-e spell?