The question is, what evidence is there that the most simple structures we can call brains are doing something which is fundamentally impossible to do with something other than a brain.
Given that brains are fundamentally governed by the same physical laws as everything else, there shouldn't be anything about them which cannot be replicated in some way by something sufficiently capable of emulation of their processes.
That's not to say it's simple. Just that brains obey the laws of physics, and as long as that's true, they should be able to be replicable.
Unless your contention is that brains are somehow able to operate outside the constraints of the laws of physics, in which case we're going to have a fundamental difference of opinion as to the nature of the universe and whether things with brains are particularly special.
This 3 pounds of meat between my ears is certainly special (perhaps the most complicated thing in the known universe) but it certainly not magical.
Just because something is non-magical doesn't mean it can necessarily be simulated by a computer, especially a practical computer that we can actually build given our level of technology and available resources.
I know you mean today, but what about in 100 years?
There are still physical limits to computation, even if we had godlike powers to rearrange the universe as we like (Bremermann's limit, Landauer's principle, there are probably others but I'm not a computer scientist or physicist). More practically, the mass and energy we have to build and operate computers with is finite. Until we know what principles the brain actually runs on, we can't do the math to determine if its physically possible to build computers that simulate it.
That said, if we find it uses some new principle that we don't exploit in our computers, things get very exciting because then we can start trying to do that (you see a faint whisper of this in the excitement around quantum computing).
I mentioned this elsewhere, but encryption is a great example: other than the breakthrough of another sort (like quantum computing), we can easily come up with a key size that is exponentially harder to compute solutions for compared to computing power increases we can achieve. In a 100, 1000 or a million years.
What if the problems we need to tackle are of a similar complexity? Do we ever get there?
We are all holding our breath for both fusion and quantum computing, and while we know they are theoretically possible, will we ever make them practical?
"Able to be replicable" is a far cry from being practically replicable.
We are unable to get two biologically identical (or at least extremely close) brains of identical twins to develop in the same way, let alone two distinct brains, or a simulated version of a brain.
The claim is potentially equivalent to a claim that since universe is theoretically computable, we'll eventually be able to simulate it.
Not at all. I'm not saying we actually will simulate it, just that it's got the property of theoretical simulatability. Which means there's not anything magical going on under the hood. Which means consciousness isn't magic.
"What can be processed" to me implied practical utility. If you did not mean that, thanks for the clarification.
Still, to me the fact that it could be theoretically achieved with computers is not very useful if it can't be achieved practically, and that certainly makes "biological" computation different from synthetic computation.