Had some trouble following your post (in part because I don't know all the acronyms), but are you talking about the basic problem of deciding which computations a particular physical process can be said to "implement" or "instantiate"? If so, see my post at http://www.mail-archive.com/everything-list%40googlegroups.com/msg43484.html and Bruno's response at http://www.mail-archive.com/everything-list%40googlegroups.com/msg43489.html . I think from Bruno's response that he agrees that there is a well-defined way of deciding whether one abstract computation implements/instantiates some other abstract computation "within itself" (like if I have computation A which is a detailed molecular-level simulation of a physical computer, and the simulated computer is running another simpler computation B, then the abstract computation A can be said to implement computation B within itself).
So, why not adopt a Tegmark-like view where a "physical universe" is *nothing more* than a particular abstract computation, and that can give us a well-defined notion of which sub-computations are performed within it by various "physical" processes? This approach could also perhaps allow us to define the "number of separate instances" of a given sub-computation within the larger computation that we call "the universe", giving some type of measure on different subcomputations within that computational universe (useful for things like Bostrom's self-sampling assumption, which in this case would say we should reason as if we were randomly chosen from all self-aware subcomputations). So for example, if many copies of a given AI program are run in parallel in a computational universe, that AI could have a larger measure within that computational universe than an AI program that is only ever run once within it...of course, this does not rule out the possibility that there are other "parallel" computational universes where the second program is run more often, as would be implied by Tegmark's thesis and also by Bruno's UDA. But there is still at least the theoretical possibility that the multiverse is false and that only one unique computational universe exists, so the idea that all possible universes/computations are equally real cannot be said to follow logically from COMP. Jesse On Wed, Jul 23, 2014 at 9:38 AM, David Nyman <[email protected]> wrote: > Recent discussions, mainly with Brent and Bruno, have really got me > thinking again about the issues raised by CTM and the UDA. I'll try to > summarise some of my thoughts in this post. The first thing to say, I > think, is that the assumption of CTM is equivalent to accepting the > existence of an effectively self-contained "computationally-observable > regime" (COR). By its very definition, the COR sets the limits of possible > physical observation or empirical discovery. In principle, any physical > phenomenon, whatever its scale, could be brought under observation if only > we had a big enough collider. But by the same token, no matter how big the > collider, no such observable could escape its confinement within the limits > of the COR. > > If we accept that the existence of a COR is entailed by assuming CTM, we > come naturally to the question of what might be "doing the computation". In > terms of the UDA, by the time we get to Step 7, it should be obvious that, > in principle, we could build a computer from "primitive" physical > components that would effectively implement the infinite trace of the UD > (UD*). Furthermore, if such a computer were indeed to be implemented, the > COR would necessarily exist in its entirety somewhere within the infinite > redundancy of that trace. This realisation alone might well persuade us, on > grounds of explanatory parsimony and the avoidance of somewhat strained or > ad hoc reservations, to accept FAPP that UD*->COR. Should we be so > persuaded, any putative underlying "physical computer" would have already > become effectively redundant to further explanation. > > Notwithstanding this, we may still feel the need to retain reservations of > practicability. Perhaps the physical universe isn't actually sufficiently > "robust" to permit the building of such a computer? Or, even if that were > granted, could it not just be the case that no such computer actually > exists? Reservations of this sort can indeed be articulated, although > worryingly, they may still seem to leave us rather vulnerable to being > "captured" by Bostrom-type simulation scenarios. The bottom line however > seems to be this: Under CTM, can we justify the "singularisation", or > confinement, of a computation, and hence whatever is deemed to be > observable in terms of that computation, to some particular physical > computer (e.g. a brain)? More generally, can we limit all possibility of > observation to a particular class of computations wholly delimited by the > activity of a corresponding sub-class of physical objects (uniquely > characterisable as "physical computers") within the limits of a > definitively "physical" universe? > > This is where Step 8 comes in. Step 7 seeks to destabilise our naive > intuition about an exclusive 1-to-1 relationship between computations and > particular physical objects by pointing to the consequences of a physical > implementation of UD*. Step 8 however is a change of tactic. First, it > postulates a scenario where physical tokens have been contrived to > represent a "conscious computation" (either in terms of a brain or in terms > of a substitute "computer"). Then it sets out to shows how all putatively > "computational" relations between such tokens could in principle be > disrupted without change in the net physical action or environmental > relations of the system that embodies them. Step 8 differs from Step 7 in > that it seeks in the first instance to undermine the very notion that > physical activity can robustly embody *any* second-order relations above > and beyond those of net physical action. Accepting such a stringent > conclusion would then seem to rule out CTM prima facie. The only > possibility of salvaging it would lie in an explanatory strategy in terms > of which computational relations take logical precedence over physical > ones. Given that computational relations are effectively arithmetical, this > in turn leads to the conclusion that CTM->UD*->COR (or more generally, that > each implies the others). > > Notwithstanding this it would seem that Step 8 is not wholly persuasive to > everybody, so is there yet another tack? The line of argument that I've > been pursuing with Brent has led me to consider the following analogy, > which I'm sure you'll recognise. Consider something like an LCD screen as > constituting the "universe of all possible movie-dramas". In terms of this > analogy, what are the referents of any "physical observations" on the part > of the dramatis personae featured in such presentations? IOW what are we to > suppose Joe Friday to be referring to when he asks for "Just the facts, > ma'am"? Well, the one thing we can be sure of is that NO such reference can > allude to the "underlying physics" (i.e. the pixels and their relations) of > the LCD display. If this analogy holds, at least in general outline, what > justification, under CTM, could remain for any assumption that our own > observations and references might "accidentally" allude to some > "LCD-physics" postulated, mutatis mutandis, as underlying the COR? Would it > not seem extraordinary that any such underlying physics could contrive to > "refer to itself" through the medium of its merely computational > derivatives? > > This last point might seem determinative, but might there not still be a > last-ditch redemption, of a physics underlying computation, in terms of > "evolution"? IOW, might it not be argued that the acquisition of internal > "computational" models of their physical environment confers a survival > advantage on the physical creatures that embody them? But any such argument > would, of course, be completely circular; assuming CTM, it begins and ends > in the COR. IOW, arguing in this way would be to ignore the fact that the > history of such creatures, their survival, and the environment in which > this is supposed to take place, all lie within the COR, not the putative > regime of any "underlying physics". THAT "physics" would necessarily be > entirely inscrutable and inaccessible for reference at the level of the COR > (think of the LCD analogy). And hence we simply would have no a priori > justification for assuming the observational physics of the COR to be > isomorphic with some notional underlying "LCD-physics". In fact, once > having assumed CTM, we would have no further basis for assigning THAT > physics any role whatsoever in our explanatory strategy. > > David > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
