Well, I only know how to define computability in terms of Turing machines.
For math I don't have a fix definition, but it's surely a bit more specific than that (e.g. I wouldn't consider the computation that prints a 0 at the same place for infinity math) - but of course I do see the circularity in my argument: a Turing machine is a mathematical object in and of itself. Though being able to talk about something doesn't necessarily change which is "bigger".
As for the other direction, this gets a bit more into the philosophy behind math itself. Constructive math's territory is "easy" - but I am on the opinion that if humans (or any intelligent physical entity) are at most Turing-complete [1], then any non-constructive math "steps" or thoughts must also be at most computable. Well, unfortunately I can't prove whether math done by transcendent entities are also computable, though.
In any case, I am no mathematician, so whatever I think regarding this topic may not have much relevance to anyone, only done CS course with quite a bit of math, but that's obviously not the same.
[1] I believe religion is an escape hatch here from an argument perspective
> if humans (or any intelligent physical entity) are at most Turing-complete
This is a bit of a strange assumption to make. I do agree that a human, if it had infinite memory, would be an universal machine, i.e. capable of computing any given Turing machine [0]. But would that be the limits of its capabilities? It's far from certain.
You'll get into the philosophy of free will (funnily enough, a sort of inverted Turing test), i.e. for a given human with infinite memory, is there a Turing machine that exactly replicates the behavior of that human? Is our behavior governed entirely by rules? Would that imply that a human themselves is a kind of Chinese room [1]?
> any non-constructive math "steps" or thoughts must also be at most computable.
What does it mean for a "thought" to be computable? Compare to Gödel's incompleteness theorem. Clearly the act of stating the thought, or writing down the theorem, is computable. But proving it to be true or false may very well be impossible.
[0] https://en.wikipedia.org/wiki/Universal_Turing_machine [1] https://en.wikipedia.org/wiki/Chinese_room
> What does it mean for a "thought" to be computable?
Well, given our scientific knowledge it's a molecule-level (only important to disregard quantum physics to make the case easier) physical/chemical process, that we should in principle be able to simulate on any other medium, including a Turing machine.
Nonetheless, I can accept the definition of math where it's about "truths" and truths can obviously exist without being computable.
> But would that be the limits of its capabilities? It's far from certain.
Do you agree that humans are physical systems?
My understanding is that any physical system can be evaluated to any degree of accuracy by a computer, no?
> any physical system can be evaluated to any degree of accuracy by a computer
That's an interesting hypothesis, but I don't know why you'd assume it to be true at face value. It's a bit unclear how you would even define "evaluated", given that we don't yet have a mathematical model of all of physics as we know it. [0] And then consider unknown unknowns.
> Do you agree that humans are physical systems?
Do you consider humans _with infinite memory_ as physical systems? Do you consider computers _with infinite memory_ as physical systems?
[0] https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Mo...
I agree that physics being simulated is not that easy to handwave away. That's why I mention that brains probably don't "depend" on some quantum-level behavior and a more macro view of physics could be enough. What I mean here is that while there are obviously quantum effects in play at the atomic/molecular levels, if we take the cells as a black box and replace them with statistical processes, we would probably still get a human intelligence as a result - but of course I can't prove it. As a hunch, the 100 billion neurons and their 100 trillion connections, and of course their environment (glial cells are important)'s proper Simulation is enough.
As for the infinite memory, Turing machines have this nice property that they can only visit a finite amount of memory after finite steps, no matter what. A Turing machine running for a finite time (we got this) will surely use a finite space, so being "a bit short" on infinite space is not a problem, I believe.
> given that we don't yet have a mathematical model of all of physics as we know it
Yes... but that's in the area of the big bang and black holes. My understanding is that the chemistry of the brain is very well modeled.
So, unless we find unknown physics, and unless that physics behaves differently than every other known physics, humans are computable?
Do I have that right?
Let me illustrate with an example. Are you familiar with with the Collatz conjecture? It's an example of a system with only one variable, and two simple rules. Are you certain that there exists a computer program that in finite time can compute where any given integer ends up?
Now consider throwing a ball in the air. Can you even write down the rules that each of the ball's subatomic particles obeys? How can you be certain there exists a computer program that in finite time can predict where any of the particles, for any ball, ends up?
> the chemistry of the brain is very well modeled
There are models, but the fact of those models is that they do not apply to "any degree of accuracy", as you claim.
Consider the ball thrown in the air again. Is the ball affected by what happened 100 years ago, inside of a black hole 100 light years away? Why would it not be affected by that? Or if you grant that it is affected by that, do we then need a model to predict those effects before we can "evaluate" them?
EDIT regarding the below linked blog post: Did you read the rest of my comment? Did you even read the blog post you linked to?
> We certainly don’t have anything close to a complete understanding of how the basic laws actually play out in the real world — we don’t understand high-temperature superconductivity, or for that matter human consciousness
Can you try to consider my central point before replying: Are the rules governing physical reality simpler or more complex than the Collatz conjecture? Does there exist a (theoretical) computer that can "evaluate the Collatz conjecture to any degree of accuracy"?
EDIT 2: I'm not the one moving goalposts. On what grounds are you classifying the question whether a given number ends at 1 or not for the Collaz conjecture as an "inifite" computation? It's a simple boolean question, yes or no. All you have to do is build a computer that can answer yes or no for each integer. Isn't that simpler than answering the position of each atom in the ball after the throw? Each is just a function, what makes one more infinite than the other?
Also, regarding determinism, just read this article by the same guy you linked: https://preposterousuniverse.com/blog/2011/12/05/on-determin...
> For everyday-life purposes, we can’t get around the fact that quantum mechanics makes it impossible to predict the future robustly.
> There are models, but the fact of those models is that they do not apply to "any degree of accuracy", as you claim.
Are you sure?
https://preposterousuniverse.com/blog/2010/09/23/the-laws-un...
Friend, I'm not going to chase your ever changing text. Please just use the reply button.
> For everyday-life purposes, we can’t get around the fact that quantum mechanics makes it impossible to predict the future robustly.
You've moved the goalposts again. I said simulate, not predict. It is possible to simulate the entire Schrödinger wavefunction.
And PLEASE - just use the reply button. It is impossible to track every time you edit your comment.
PLEASE just stop complaining about "moving the goalposts" when the issue is your own lack of clarity of both expression and reasoning. WHAT is the distinction between "simulate" and "predict"? You said neither by the way, you said "evaluate".
> ANY physical system can be evaluated to ANY DEGREE of accuracy by a computer
It's completely SENSELESS to claim that they are distinct, because in order to EVALUATE or SIMULATE the physical system you will need a FUNCTION which COMPUTES the STATE of the system at a given point in time. The only POSSIBLE distinction between SIMULATING and PREDICTING would be the time taken for the computation, but that is COMPLETELY IRRELEVANT as long as it is finite.
Again, your own source says:
> We CERTAINLY don’t have ANYTHING CLOSE to a complete UNDERSTANDING of how the basic laws actually play out in the real world
How does that square with your claim above?
> You said neither by the way, you said "evaluate".
You are entirely correct. I was sloppy in my first comment. I should have said simulate. My sincere apologies if that's been the crux of our dispute.
> The only POSSIBLE distinction between SIMULATING and PREDICTING would be the time taken for the computation
No. The distinction is in determining which "you" is you. When simulating the wavefunction, every you is simulated.
> We CERTAINLY don’t have ANYTHING CLOSE to a complete UNDERSTANDING of how the basic laws actually play out in the real world
It's very understandable if you include his following sentence:
> But these are manifestations of the underlying laws, not signs that our understanding of the laws are incomplete
He's saying we don't understand emergent behavior produced by the laws - not that the laws themselves are incomplete. E.g. we don't know how/why a bag of neurons turns into a person.
Re: Collatz - you've moved the goalposts. Answering Collatz requires solving a halting problem. I didn't claim that I could find the end of an infinite computation. I claimed to be able to simulate a finite one.
And - you should reply to my comments rather than edit your old ones.
No
HEH. Well... the only other option is supernatural. Is that what you mean?
Does that mean that humans could produce mathematical proofs that are entirely logical and verifiable by other humans, but that cannot be formalised in any automatically verifiable language such as lean?