Joel: ... But there MAY be some reasons to want to know exactly which algorithm is really being run on the bottom...
Bruno: I am not sure there is any (absolute) bottom. Joel: Mustn't we assume there is? If there is no bottom, what will we stand on? How can we understand anything at all? I wrote this to the list a while ago: Gerard O'Neill, the late Princeton physicist best known for his space colony studies, once said that if you met a race that insisted that logical developments must be built step by step from a firm foundation, you could be pretty sure they were planet dwellers. Races that live in space realize that it's perfectly OK to build structures that have no foundation at all. They can be circular and unsupported, yet if you spin them they'll have gravity just like the ponderous planetary piles! The context, related to the discussion above, was the need for a logical foundation for objective attributions of consciousness. more: Many of the people on this list (in common with a lot of western philosophy at least since Descartes) are hoping to construct their existence measures on the bedrock of the objectively decidable self-awareness. They've built very interesting structures, but you may notice there's been no progress at all on stabilizing the foundation. Instead we have on this list the same debates that endlessly, repetitively and inconclusively flood comp.ai.philosophy, never mind philosophy journals and books. I think the insistence on the absolute underpinning of an objective consciousness is just planet-bound thinking. Bruno's, Juergen's, Russell's or Max Tegmark's analyses can just as well be built on arbitrary selections of what's conscious (Turing test passers? biological brains? red-haired people? teddy bears?). The teddy bear universes may have different probabilities than the biological brain universes or the Turing test universes, but so what? Each is as likely to be self-consistent as another. i.e. You don't have to give up the goals of this list just because you don't believe there is an objective fact of the matter to consciousness.