[knzhou]

This argument proves too much. By that same argument, nuclear fission, ordinary CPUs, steam engines, rockets, helicopters, jets, X-rays, radio waves, superconductivity, superfluidity, air conditioning, liquid helium, liquid nitrogen, the Haber process, the fractional quantum Hall effect, Doppler cooling, graphene, long-distance satellite communication, gravitational waves, and GPS corrections for relativity all don't exist, because nothing in life is designed like them or takes advantage of them. You've literally taken us back to the 1700s.

I know that it's fashionable to simply declare quantum computing is impossible, and there are some strong arguments in this direction, but this particular argument isn't one.

The general reason people believe quantum computing is possible is that it describes just about all the things I mentioned above absolutely perfectly, along with literally thousands of other phenomena, with no deviations ever measured. This gives us good reason to assume quantum mechanics actually works, and if it does, then it's possible for quantum computing to work. (Also, of course you need to account for quantum mechanics to account for protein folding. You literally can't have chemical bonds at all without quantum mechanics.)

[Iv]

The argument I propose is not a strong one. It is still an argument: if something is possible, why did evolution not use it? There are several possible answers:

1. Life may not have a use for it

2. It may be impossible to achieve with proteins and cells

3. It may not actually be possible

For quantum computer I (weakly) believe that 1 and 2 are wrong: evolution and cognition would hugely benefit from quantum acceleration and biology operates at a scale where quantum effects are visible. I thought 3. slightly more likely but I'll readily admit that I am nowhere near the knowledge to be categorical about 2.

And note that of the list of things you are giving, there are many that uses the same physical principles that are used by life: steam engine (expansion of heated gases), rockets (ignition of gas), jets (propulsion), helicopters (a rotating wing is a wing), radio waves/X-rays (the RF spectrum, which visible light is part of), etc... The rest, IMO, falls either under 1. or 2. For instance I doubt long-distance communication really offers a substantive advantage when you know whales can already contact each other at 100s of kilometers through shouts, and superfluidity may require conditions and materials that are impossible to reach for organic material.

Note however that this last one is actually a kinda good (if weak) argument: if superfluidity was achievable through organic material and conditions close to the temperature and pressure average on earth, life would probably have found it, as it is clearly a useful property. If tomorrow we find that you can get room-temperature superfluids that are made out of C,H and O atoms, wondering why it is not found in nature will be a very good question.

[sriku]

All that is assuming that you do know for certain the evolution did NOT exploit it.

There is some extrapolative argument that hints at the contrary. Adrian Thompson's evolved FPGA circuits exploited a single chip's underlying physics in a manner no digital circuit designer would. By that thread, it would seem possible that evolution has already exploited quantum computation ... just that maybe we haven't had the tech eye to see it yet.

After all, all systems are quantum mechanical.

[smilliken]

Rhodopsin, in our retina, exploits a quantun mechanical effect. You could argue that our brains are quantum computers if you consider our retina including rhodopsin to be part of the brain.

[whatshisface]

Apples are red because of quantum mechanical effects, but that doesn't make them computers.

[smilliken]

Anything and everything is because of quantum mechanics, sure. But you could've asked a classical physicist to design an apple "computer" (the fruit)— just arrange the right atoms— but you couldn't have asked a classical physicist to design a retina computer exploiting rhodopsin.

[simonh]

I don't think 2 is so easy to justify. Quantum state transitions occur all the time in a discordant mess of activity at room temperatures. The only way we can control for that and have quantum transitions occur in useful controlled circumstances is by operating at close to absolute zero, which isn't very conducive to exploitation by terrestrial life.

It may turn out to be a similar issue to jet engines, or semiconductors. The materials and conditions required for them to operate just aren't very easy for terrestrial life to evolve into.

[soulofmischief]

Nature works on the premise of emergence. It's entirely possible that the energy gradient required for a biological system to make successful, permanent changes beneath its fundamental layer of operation is just too much.

Suppose this all started with a few self-replicating proteins. From that we got organelles, and then cells. Then multi-cellular organisms, then tissues, organs, etc.

But working backwards, from protein -> molecular chemistry -> quantum phenomenon, may simply not be the path of least resistance and thus for the overwhelming majority of life in the universe, was not an evolutionary path.

[knzhou]

The answer is a combination of 1 and 2. Not every computing device is actually useful. For example, you can find plenty of brain parts that look vaguely like GPUs or FPGAs. None that look anything like a standard CPU. This would be basically impossible to build out of cells, and not useful anyway.

The same thing applies to quantum computers. They’re much much harder to build because they’re more delicate. We’re talking about effects that usually are completely destroyed by a single unwanted atom coming in and hitting something. And there are a lot of atoms flying around in cells. Propagating any quantum signal from even one cell to an adjacent one is impossible. Finally they’re less useful. I can’t think of problems a biological brain needs to solve that require even a moderately fast CPU, let alone a quantum computer, which provides speedups over the CPU for only certain specific problems.

But none of this really matters, because your comment is one long isolated demand for rigor. You wave away my long list of examples because you think something very distantly related exists (in which case, with those low standards, quantum computers already exist), or because the examples are clearly impossible or not useful (without equally seriously considering the same for quantum computers). This is what I mean by skepticism of QC being driven mostly by intellectual fashion.

[peteradio]

It's 2. There is no way for cell/proteins to maintain a useful small scale quantum state.

[raverbashing]

I think in your list of examples there are plenty of cases where nature, while not building the exact thing uses the same underlying principles.

There are a lot of seeds that are aerodynamic so that they get spread more widely for example. Even seeds that have controlled falls due to "autorotation"

But of course on planet earth at least it is hard for nature to use things requiring too high or low temperatures. Nature doesn't need the Haber process, but it does fixate nitrogen.

[simonh]

Right, so life could make use of quantum transitions that are used in quantum computing, without actually doing or using the results of quantum computations.

[knzhou]

If your standards are low enough that you would say superconductivity appears in nature, then quantum computing certainly does.

[raverbashing]

> But of course on planet earth at least it is hard for nature to use things requiring too high or low temperatures

So, no, superconductivity probably does not exist in nature

[knzhou]

Most candidates for quantum computing also require extremely low temperatures — in fact, lower than the ones for superconductivity.

[kuschku]

> nuclear fission

https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...

For pretty much every thing you list, nature has something pretty close to it in it. Even nuclear fission.

[gilleain]

Although natural, that reactor is geological not biological.

It's unlikely that enzymes could catalyse fission reactions. It would be amazing if they could...

[knzhou]

If you really think you can explain all examples, why did you pick one (by far the easiest one) instead of letting me pick? Let’s see some natural examples that use general relativity, superconductivity, the fractional quantum Hall effect, and superfluidity.

[emilfihlman]

Wtf? Non even remotely the same argument.