"[the mind] could be a physical system that cannot be recreated by a computer"

Let me quote an argument in favor of this, despite the apparently near universal consensus here that it is wrong.

There is a school of thought that says, OK, let's suppose the mind is a computation, but it is an unsolved problem in philosophy how to determine whether a given physical system implements a given computation. In fact there is even an argument that a clock implements every computation, and it has yet to be conclusively refuted.

If the connection between physical systems and computation is intrinsically uncertain, then we can never say with certainty that two physical systems implement the same computation. In particular, we can never know that a given computer program implements the same computation as a given brain.

Therefore we cannot, in principle, recreate a mind on a computer; at least, not reliably. We can guess that it seems pretty close, but we can never know.

If LessWrongers have solved the problem of determining what counts as instantiating a computation, I'd like to hear more.