Re: Djinni vs. White Rabbit
On Aug 19, 2004, at 2:00 PM, Hal Finney wrote: It's not clear to me that causality and time are inherent properties of worlds. I include worlds which can be thought of as n-dimensional cells that satisfy some constraints. Among those constraints could be ones which induce the effects we identify as causality and time. For example, a two-dimensional cell where C[i,j] == C[i-1,j] XOR C[i-1,j-1]. This particular definition has the property that C[i,.] depends only on C[i-1,.], which lets us identify i as time, and introduce a notion of causality where conditions at time i depend on conditions at time i-1. But we could just as easily create a cell system where there was no natural definition of time, where C[i,j] depended on i+1, i-1, j+1 and j-1. You could still imaging satisfying this via some constraint satisfaction algorithm. +1 I'll have to think about the CA implications --- what is a "cell" in such a CA, and what is meant by the various "nearness" relationships of such cells? (I'm still processing Wolfram's book, a couple of years after reading it the first time. ;-) I'm just adopting a relatively conventional GR point-of-view here, where time is just another direction, albeit one in which travel is (in most circumstances, depending on the local differential geometry and geometrodynamics) directionally constrained. (I'm ignoring the thermodynamic interpretation of time's arrow, though when you throw 2LT into this particular brew things would seem to get rather interesting. ;-) Now these jinni worlds are ones which mostly have these conditions we identify as time and causality, but which locally, or perhaps rarely, do not satisfy such rules. Seen in this perspective, there is a full range of possibilities, from fully causal worlds, to ones which are 99.999% causal and only .0001% noncausal, to ones which are 50-50, to ones for which no meaningful concept of causality can be defined. We're begging the question re: causality; it was perhaps unfortunate that I chose to use that word, as it's interpretive rather than descriptive in itself. The argument Boulware's making appears to be inherently probabilistic and geometric rather than ontological. That became less clear in my exposition, my bad. I'll have to look at this. It doesn't sound quite right. If probabilities are non-unitary that violates the fundamental rules of QM, But do they? This is, I think, perhaps a very interesting and pertinent question. It certainly appears to throw both the QM formalism as well as its interpretations into disarray, but I think perhaps the result is less than fatal. One can certainly do statistics (and hence QM) with non-unitary probabilities --- the method involves a kind of normalizing transformation between different probabilistic measures. (In fact this very issue was dealt with by one of Gott's grad students; the citation escapes me at the moment, but he found that you could patch things up by simply supplying a kind of local correction coefficient. I.e., while this appears prohibitive on the surface, in fact "fixing it up" isn't all that difficult. The ontological interpretation of the relationships between these patch coefficients, OTOH, is IMHO pretty surreal.) I think you're getting awfully speculative here. This is a criticism, in *this* group in particular? ;-) It's admittedly speculative. It sounds like you are suggesting that it would be simpler to suppose that "all universes exist which contain jinn" than "all universes exist". Not precisely; I'm suggesting that "simple" is difficult to measure when speaking about TOEs. There might be some measures of "simple" for which the above is true; there are others, e.g. the Champernowne machine and so forth, for which it is certainly not. But Occam's Razor isn't much help here by itself. That doesn't seem at all plausble to me. My heuristic is that any rule of the form "all universes exist except X" is going to be more complicated than one of the form "all universes exist". On the surface, sure. But consider: the statement "all universes exist" presupposes a definition of universe that it omits. What is meant by "universe" requires an exhaustive definition, and the algorithmic hypotheses make varying assumptions about that definition. My intuition would be that the most parsimonious definition would be the preferable one; but we don't have any metrics for "parsimony" on such definitions. It could be that definitions that statically embed such jinn might be more parsimonious by some measure than other ones; the statically-defined jinn might "ground out" the definition and permit a higher-order / more abstract / terser "universe generation algorithm." (Think Python vs. its own bytecode.) Think of it this way: any formal system has its base axioms. In this context, the "universe generator" is the system in toto; the jinn could form (at least a part of) its axioms. Or, thinking abou
Djinni vs. White Rabbit
At some point in the past various of us have argued about whether the simulation argument and / or the multiple worlds interpretation of quantum mechanics implies an "every possible world" (EPW) interpretation, i.e. one in which highly improbable events, laws of physics, etc. obtain. Stumbled across an interesting if tangential paper that has something to say about this. First some terminology: let's call events that are highly improbable "white rabbits" and universes in which such events happen frequently (or universes with entirely inscrutable laws of physics) "white rabbit worlds." Let's further adopt the term "djinni" or (to follow Gott's nomenclature) "jinni" to refer to closed time-like (causally cyclic) curves, and "jinn worlds" as worlds (n-dimensional "spacetime" slices of the higher-order spacetime, or rather n-m dimensional phase-space volumes where n is the total dimensionality of the phase space) that contain such causal cycles. In order to explain what this means: these are causally consistent chains of events in which there is no ultimate cause, but rather a closed causal chain that traverses both forward and backward along the time dimension. A peculiarity of this idea is that, in such a world, information "appears" without cause. For example a computer employing a closed time-like curve as a register can compute "hard" problems, but when one examines the execution history of the computer through time one finds that it never actually executes the computation! Cf.: http://arxiv.org/pdf/gr-qc/0209061 Anyway, "jinni" are these little closed curves of causality in the presence of time travel that are consistent but defy common sense. David G. Boulware of the University of Washington published this paper in PRD: http://arxiv.org/abs/hep-th/9207054 ...in which he studies the behavior of quantum fields in spaces with closed time-like curves. What he finds is that probabilities are not "conserved", i.e. not unitary, in such spaces. That is, the Feynman sum-over-histories approach always yields precisely 1 --- except when space contains one or more jinn. In such cases, there are quantum events that simply cannot occur. So: jinn defeat white rabbits. If any world-line through the phase space is cyclic / allowed to self-intersect, the overall phase-space is constrained, presumably to those set of configurations which are of higher probability. The very existence of such causal cycles may indeed be --- meta-paradoxically ;-) --- essential in stabilizing the overall structure of the phase space. It would seem that these cycles act as a kind of strange attractor around which probable configurations (universes) coalesce. Speculation: it may be that through studying the impact of such closed time-like curves in various spacetimes that we ultimately reconcile Cramer's transactional interpretation (retarded waves moving forward in time, advance waves reaching back to "handshake" on each quantum event, producing a kind of causal contract) of QM with MWI --- and ultimately COMP. Indeed, each retarded wave-advance wave pair *is* a jinni. Cramer doesn't just embrace jinn in his interpretation --- he bases the whole idea on their existence! (FWIW: this seems to me an embarrassment of riches. Why should *every* quantum event require a jinni, when a few --- acting as strange attractors --- might suffice? Though admittedly the latter leads to the questions which few, and why?) The implication ala Boulware is that if this is a real physical effect, then this provides a kind of global probabilistic censorship that makes the world the predictable place that it is! And --- connectionism --- it's rather ironic that Cramer's transactional hypothesis is based in part on some of Feynman's own speculation, when Feynman probably didn't realize the essential seemingly paradoxical consequences of pairing the histories approach with cyclic causality. So that's all well and good for physics, but what about the more algorithmic cosmologies? One school of thought regarding the COMP hypothesis is that it is easier to simulate all possible worlds than it is to simulate any subset of them. (Cf. previously-discussed Champernowne machine / "everything" algorithm.) But what if the dynamics of the simulation are such that these jinni exist as a priori structural parameters, "roots" if you will of the computation? In such an environment, "every computable universe" is NOT every possible universe. Curiouser and curiouser, jb
Re: Many Worlds invalidated?
BTW, just a caveat --- and I should've caveated the initial forward. I'm not endorsing this or any interpretation of this experiment at all, rather just offering it up to the list in case others had not seen it. $0.02, jb On Apr 26, 2004, at 2:34 PM, Jesse Mazer wrote: Hal Finney wrote: The MWI is just the quantum formalism minus wave function collapse and is therefore perfectly compatible with this experiment, since the experiment is itself compatible with the quantum formalism. Would this experimental result actually be predicted by the quantum formalism, though? It sounds like they had a setup similar to the double-slit experiment and found a small amount of interference even when they measured which hole the particle traveled through, but I thought the quantum formalism predicts that interference would be completely destroyed by such a measurement. Either way, the claim that this supports the transactional interpretation but not the MWI interpretation can't be right, since both are supposed to be equally compatible with the quantum formalism. Jesse _ Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage! http://join.msn.com/?pgmarket=en-us&page=hotmail/es2&ST=1/go/ onm00200362ave/direct/01/
Many Worlds invalidated?
Hot off the press, via Boingsters: http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html Many Worlds theory invalidated Kathryn Cramer breaks the story on a to-be-presented Harvard talk on an experiment that appears to invalidate both the "Many Worlds" and "Copenhagen" theories of quantum mechanics. Kathryn is the daughter of John Cramer, a physicist whose "Transactional Interpretetation" hypothesis is the only one left intact by the experiment's findings. It has been widely accepted that the rival interpretations of quantum mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds Interpretation, and my father John Cramer's Transactional Interpretation, cannot be distinguished or falsified by experiment, because the experimental predictions come from the formalism that all such interpretations describe. However, the Afshar Experiment demonstrates in an interaction-free way that there is a loophole in this logic: if the interpretation is inconsistent with the formalism, then it can be falsified. In particular, the Afshar Experiment falsifies the Copenhagen Interpretation, which requires the absence of interference in a particle-type measurement. It also falsifies the Many-Worlds Interpretation which tells us to expect no interference between "worlds" that are physically distinguishable, e.g., that correspond to the photon's passage through one pinhole or the other. Link (Thanks, Kathryn!) http://www.kathryncramer.com/wblog/archives/000530.html
