It is without question possible, because we exist. It is also possible to do it quickly, because again, we exist. The only thing that is unclear is:
1. How hard it is to do artificially.
2. How far from optimum the human mind is, and how complex it is to improve upon it.
Of course we have absolutely nothing to indicate that would be the case, but we also don't understand the brain well enough yet.
I think it'd be highly improbable, but looking at the crude simulations we do of computers etc. today, it certainly is likely that simulations would use "dirty tricks" to get more out of the available computational resources, and finding artefacts of such dirty tricks or shortcuts could at least in theory be possible. Of course, the absence of such artefacts unfortunately proves nothing, so the whole thing does have a bit of a "how many angels can dance on pin" feel to it. But it's fun to think about the possible implications.
Personally I especially like to bring it up if people try to discuss religion with me.
Nature is pretty good at optimization. We can often build devices that out perform animals on certain characteristics, but that's because we've limited the scope of what they do and we aren't concerned with the energy requirements. We also know that, as interesting as our brains are and as powerful as they are at certain kinds of problems, they aren't the best at all of them. For instance, chimps appear to have a significantly better short term working memory. It is possible that we are already close to optimum for the kind of intelligence we are interested in. I suspect that if we manage to significantly improve upon it, it will be because we don't have to concern ourselves with the energy requirements.
Only if there is a benefit to doing so. If it was simply a case of "nature can optimize really well" then we would expect to find many species at or near the limit of intelligence, not just one. Other species did not have the evolutionary pressure to cause as high of intelligence to be selected for. It is very reasonable to think that we also did not have the evolutionary pressure necessary to cause us to have even higher intelligence than we do.
> It is without question possible, because we exist. It is also possible to do it quickly, because again, we exist.
It's apparent that we don't know everything.
I think I feel comfortable saying that it is possible to do with the technology we have. Because 'intelligence' is almost certainly some form of computable function, which means that a turing complete computer can compute it.
It is of course possible that there exists some special function outside of turing completeness and intelligence is one of those, but we don't know of anything like that, so the best bet to make is that that is not the case.
> It's apparent that we don't know everything.
No, but we do know some things. And thus far we've been able to at least begin to design systems capable of performing any well-defined task. We don't have any reason, at the moment, to believe synthesizing an intelligence is an especially difficult problem, relative to say, lots of other open problems in science and technology.