How likely is it that any type of non-biological human-level Artificial Intelligence is possible in principle? Include simulations of the human brain ("neuromorphic AI"). Ignore whether or not it will actually be created in practice — just state whether it's possible in principle.
"'Could a machine think?' On the argument advanced here
only a machine could think, and only very special kinds of machines,
namely brains and machines with internal causal powers equivalent to
those of brains. And that is why strong AI has little to tell us
about thinking, since it is not about machines but about programs,
and no program by itself is sufficient for thinking."
Implication: AIs based just on running programs will not work, so non-biological AI in general may not be possible.
Source: Searle, John R. "Minds, brains, and programs." Behavioral and Brain Sciences 3 (1980): 417-57. 8 Aug. 2008 <http://www.bbsonline.org/Preprints/OldArchive/bbs.searle2.html>
human brain is not a computer, and therefore cannot be simulated by
a digital computer.
Implication: Any kind of human-level AI is implausible, even given arbitrary computing power.
Sources: Michael Denton, William Dembski, and others in Are We Spiritual Machines?
people say that computers can never show true intelligence, whatever
that may be. But it seems to me that if very complicated chemical
molecules can operate in humans to make them intelligent, then
equally complicated electronic circuits can also make computers act
in an intelligent way. And if they are intelligent, they can
presumably design computers that have even greater complexity and
Implication: Artificial intelligence is possible.
Source: Stephen Hawking. (2007). http://www.singinst.org/summit2007/quotes/stephenhawking/
consciousness and creativity are based on quantum effects unique to
Implication: Non-biological AI is unlikely.
Source: Penrose, Roger. (1989). The Emperor's New Mind. Oxford University Press.