X-Message-Number: 11575 Date: Mon, 19 Apr 1999 01:34:01 -0700 From: Mike Perry <> Subject: Quantum mechanics, many-worlds, etc. Thomas Donaldson, in #11566, notes that relativity and quantum mechanics haven't been harmonized yet, which is my understanding too. This could spell trouble for any arguments or extrapolations that depend too heavily on one or the other of these theories being correct or at least very nearly so. On the other hand, though (and I'm not an expert on this but it seems to be a reliable conclusion) there are efforts underway to reconcile the two, and it appears that such a reconciliation is possible without bending either theory too much. At least the outlook seems reasonably hopeful. A reference to this is in Moravec's new book, *Robot: Mere Machine to Transcendent Mind*, p. 214, note 11. Interestingly enough, the "bending" in this case would appear to affect relativity, not quantum mechanics, in that it calls for time and space to be discretized on very small scales, rather than being the familiar continua they have seemed to be for so long. I also see a flaw in Thomas's argument: >Furthermore, the claim that we can use a Cantor-like argument to show that >no possible finite computer can produce all possible worlds does not show >the nonexistence of SOME finite computer capable of producing any >arbitrary possible world. If we replace "possible world" by "computable function" we see that there are functions that no computer can compute. I.e. we can't just specially-design one computer to compute such a function. No such computer is possible, even in principle. And on the other hand, there *does* exist one particular computer that, with suitable programming, can compute any function that any other computer can compute. The same sort of argument is used by Deutsch in his claims about which worlds are producible by a computer and which are not. Thomas also says >... but whoever said that we must remain of any fixed size? With that I completely agree. Bekenstein bounds and discreteness would not preclude the possibility of indefinite growth in an expanding universe, and thereby, immortality. Bob Ettinger, in #11569, raises the possibility that the Schorr factorization algorithm might be explained as an analog effect of some kind, without invoking the many-wprlds idea of quantum mechanics. It is worth pointing out that the many-worlds theory accounts *in detail* for how the algorithm is supposed to work, in a reasonably straightforward (if complicated) way. In particular it accounts for how a quantum device could perform the factorization more efficiently than any classical computer, this being where the parallel universes come into play. Any rival theory worth its salt must do the same. So far, I haven't heard of any such rival. It's true that there are single-world theories that make the same predictions. But (and Deutsch discusses this in his book) they seem to be forced into the position of asserting that things behave "as if" there were many universes, etc., and thus to be contrived explanations. Bob also says, >I was going to stop here, but as long as I'm gnawing on Deutsch I may as >well mention another defect in his book as it seems to me. He claims that >interference effects prove the many-worlds hypothesis, and talks about >photons interfering with each other, and discusses some well known >experiments. But interference is most easily understood as a wave >phenomenon, and nowhere does he so much as mention waves, let alone some >way of reconciling the famous wave/particle dualism. The "wave" explanation of interference effects breaks down when only one photon at a time is involved. How does that one particle manage to interfere with itself? A straightforward answer is that "something" is nudging that photon, one or more "ghost" photons from parallel universes. Bob adds, >Unless I have been totally oblivious, he has provided no explanation for >interference. Starting on p. 41, you can read about an interesting variation of the famous two-slit experiment, that is, a four-slit experiment, in which half of the interference bands that you get with two slits are virtually cancelled out. The explanation of this is, again, that "ghost" photons from parallel universes are nudging "our" photons so they don't strike where they otherwise would. So how is this "no explanation for interference"? (The "ghosts" by the way, are just as "real" as the "real" particles, just parts of other "real" universes than our own.) Mike Perry Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=11575