From stapp@thsrv.lbl.gov Tue Apr 25 14:27:36 2000 Date: Tue, 25 Apr 2000 14:20:00 -0700 (PDT) From: stapp@thsrv.lbl.gov Reply-To: hpstapp@lbl.gov To: kleinlist , bdj10@cam.ac.uk, brings@rpi.edu, brucero@cats.ucsc.edu, chalmers@paradox.ucsc.edu, ghrosenb@ai.uga.edu, hameroff@u.arizona.edu, hpstapp@lbl.gov, Jeffrey M. Schwartz , keith@imprint.co.uk, klein@adage.berkeley.edu, patrickw@monash.edu.au, phayes@ai.uwf.edu, Kathryn Blackmond Laskey Subject: Re: Deutsch claims Q-info is local (fwd) ---------- Forwarded message ---------- Date: Tue, 25 Apr 2000 14:16:21 -0700 (PDT) From: stapp@thsrv.lbl.gov Reply-To: hpstapp@lbl.gov To: augustyn@erim-int.com Subject: Re: Deutsch claims Q-info is local On Mon, 24 Apr 2000 augustyn@erim-int.com wrote: > Dear Henry, > > http://xxx.lanl.gov/abs/quant-ph/9906007 > > In this June 99 paper, Deutsch claims that "all information in quantum systems > is, notwithstanding Bell's theorem, localised." He claims there is a wide > range > of misconceptions stemming from belief in the contrary. He defines a new > concept, locally inaccessible information, as "information which is present > in a > system but does not affect the probability of any outcome of any possible > experiment on that system alone." > > Unless I've once again misunderstood something, this paper seems to be in > direct > conflict with your theory. > > Ken > > > Dear Ken Deutsch adopts the Heisenberg picture, which is a good thing to do: I used to do that myself. Then he says that he will keep the state vector constant. This means he is adopting basically the Everett view, where there are no "reductions". All nonlocal effects are consequences of reductions, so by adopting a "no reduction" (many-worlds or many-minds) approach he avoids all nonlocal effects. The avoidance of nonlocality is THE huge virtue of the "no reduction" approach. Within the "no reduction" approach one is NOT entitled to assume that when an experiment is performed, and an observer observers the outcome, that some actual choice has been made that picks out that one outcome and eradicates the other: both outcomes exist. A second key point is that a correlation between the far-apart events is not measured, or actualized, until the outcomes of the two far-apart measurements are brought together (by classical communication mode, and at speed not greater that the speed of light)) at some later time. I stressed these points in my 1980 paper "Locality and Reality" (Found. of Phys. 10, 767) about the local character of the "no reduction" approach, and John Bell told me, to my surprise, that he thought that I was the first one to mention the latter key point. Deutsch makes important use of it in his treatment, as well as the key result in the field, which is that the PROBABILITIES for outcomes in one region do not depend on which experiment is performed in a spacelike separated region. Deutsch's paper is basically just a restatement of these well known things, specialized to the particular sort of interactions that normally occur in quantum computing. The main point is simply that the "no reduction" (many-worlds or many-minds) theory is certainly local. The question, then, is whether this virtue of being local is sufficient to make it viable?. The troubles come in only when one wants to bring in the human observers. If one brings them in then one has to reconcile the fact that a human observer experiences only one classical outcome with the fact that the theory has no corresponding "reduction": both classically represented outcomes must be carried along as existing actualities. But if there is no reduction then what prevents both one brain-state projector P corresponding to an experience, and then a very slightly different P' also corrsponding to an experience, and both experiences occurring. But then probabiliies for the different possibilities will not add to unity. The vN/W theory invokes the key vN process I (von Neumann reduction) S--> PSP + (1-P)S(1-P), to make the probability calculus work. I follow THAT approach. Henry From stapp@thsrv.lbl.gov Thu Apr 27 11:26:05 2000 Date: Thu, 27 Apr 2000 11:24:08 -0700 (PDT) From: stapp@thsrv.lbl.gov Reply-To: hpstapp@lbl.gov To: Aaron Sloman Cc: hpstapp@lbl.gov, bdj10@cam.ac.uk, brings@rpi.edu, brucero@cats.ucsc.edu, chalmers@paradox.ucsc.edu, ghrosenb@ai.uga.edu, hameroff@u.arizona.edu, Jeffrey M. Schwartz , keith@imprint.co.uk, klein@adage.berkeley.edu, patrickw@monash.edu.au, phayes@ai.uwf.edu Subject: Re: Deutsch claims Q-info is local (fwd) On Thu, 27 Apr 2000, Aaron Sloman wrote: > Henry responded to this: > > > On Wed, 26 Apr 2000 augustyn@erim-int.com wrote: > > > > > Dear Henry, > > > > > > Thanks for clearing that up. The many-worlds approach appears be > > > a reactionary head-in-the-sand way to avoid the problem of > > > consciousness. There doesn't seem to be anything (to my meager > > > knowledge) that explains why we are on the branch > > > we find ourselves on. I'm surprised it is so popular. > > > > > > Ken > > That objection is just silly. On the many-worlds theory (e.g. as > explained in Deutsch The Fabric of Reality (I have not yet tried to read > the more recent paper)) in each branch we, or rather our counterparts, > are ON that branch, so there is nothing to explain. > Yes. That is correct. > The question (why we are on the branch we find ourselves on) presupposes > that on the many worlds theory we are only in ONE branch, which would > have to be explained. But that would be totally inconsistent with the > theory. Yes. There are, according to MWI, other branches of Ken, and of Aaron, and each branch includes the conscious experiences that goes with it. So Aaron is quite right to point out that the question " why we are on the branch we find ourselves on" is not a problem for MWI. > > > Locality is hard for physicists to give up. > > Deutsch gives up a kind of locality insofar as he explains interference > phenomena as involving interactions between particles in alternative > universes, if I've understood him. I doubt that Deutsch explains interference in that way: in MWI the interference phenomena are between parts of a single branch. Indeed, if these physical phenemena were caused by interactions between different branches then their physical occurrences would be evidence for the existence of the other branches. But there is no such evidence. The reasons for assuming that other branches do exist are purely theoretical: that assumption saves locality and it saves the idea that the deterministic Schroedinger equation of motion (or the Heisenberg equations of motion, if one chooses to use the Heisenberg picture, as Deutsch does) always holds; that the basic eqn. does not suddenly fail when "mind" enters into the dynamics. The attitude of MWI theorists, like that of classical-physics theorists, is that mind is purely a local deterministic consequence of the physical structure described by quantum theory, and that the Copenhagen approach (or the vN/W approach) of bringing mind into physical theory was a VERY bad idea. > > When I hear scientists debating such options without any possibility of > settling which is correct, apart from personal preferences, I > immediately suspect that neither has the truth, which needs to be > formulated in such a way as to subsume both options. The differences in the "explanatory powers" of the two theories is very large. That difference provides one way for scientist to decide which theory is better, in the sense of being more useful: the capacity to provide "understanding" is a valid criterion for deciding between theories. Reduction theories can give mind real power over brain events, whereas MWI has no fixed place for mind and makes mind epiphenomenal: it says that psychological processes do not really matter. But then that theory is very flabby in terms of its predictive and explanatory power in regard to the empirical findings pertaining to how psychological processes to enter into brain dynamics, in contrast to vN/W QT, which specifies in a fair amount of detail how mind controls brain dynamics. > There is also the question of whether MWI is logically coherent as a description of the universe, including the human observers and their experiences. Deutsch is mainly interested in quantum computation, and thus he consider situations that are very specialized and idealized. But how well does MWI work for human brains and the streams of consciousness associated with them. If the Schroedinger Eqn. govern everything then the state (in the Schroedinger picture) is a superposition of a "continuum" of possibilities. For each P there are a continuum of different nearby P's that are not orthogonal to it: P P' not zero. But in a universe that is essentially a continuous superposition of all possibilities there is no way to specify, just on the basis of the evolving state, that P corresponds to a possible experience but P' does not. The problem, basically, is that in a realistic MWI universe the separation of the state into a superposition of distincts orthogonal "branches" specified by the state itself, at finite times, with no outside "observing system" or arbitrary rule, cannot be achieved: there is no intrinsic-to-the-state difference between P and P' if the state is a smeared out superposition of all possibilities. But if P and P' both correspond to allowed experiences, then the probability calculus fails. von Neumann's process I, which is a reduction process, is needed to make the probability calculus work. Each allowed experience must be associated with a P that allows the state to be decomposed into PSP + (1-P)S(1-P), where the two terms correspond to the experience either happening or not happening. If there is no such reduction and another experience corresponding to a slightly different P', with PP'not 0, can also occur, then the probability calculus collapses in ruins: neither in projections into the future nor surveys of the past will the quantum probability rules hold. For the probability for some experience to occur will be infinite, and there will be contribution to the brain state in which certain experiences have both occurred and not occurred. So I believe that MWI fails for technical reasons connected to the "choice of basis" that is needed to implement the probability calculus. This "choice of basis" enters vN/W QT as the "asking by the `person' of some particular question". This process must, I believe, be nonlocal because, in contrast to the process described by the Schroedinger equation, it concerns the (necessarily) nonlocal P. So my vN/W QT is built upon a certain mind-based resolution to precisely the difficulty that I believe wrecks the MWI. I was led to it by way of the MWI. Henry