lambert@mcvax.UUCP (06/04/87)
In article <7400@boring.cwi.nl> lambert@boring.UUCP (I) wrote: >> Here is another many-worlds interpretation of the Aspect experiment than >> the usual one. It requires no "supra-luminal collapse" of the wave- >> function and is in fact pseudo-deterministic. [...] >> Question: does this predict something different from QM? In article <5925@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) replies: > No. The "many-worlds" interpretation has been known for quite some > time to make the same predictions as the Copenhagen interpretation. Has this been shown then for *all* many-worlds interpretations? Or is there some obvious bijection between the one I gave and the well-known MWI? (In the usual version the world "forks" on the *current* *observation*; in the one I gave on *future* *experiments*.) One of the things I don't understand with the usual MWI is how it gets the probabilities right. An observing consciousness on a branching path has a history of say L and R turns; why should there be (in the case of a replicated experiment with bias) more of one sort than of another? > It also seems to lack any real explanatory advantage. A philosophy.technical point: Even if two theories are isomorphic, it may be the case that one admits of or even invites certain variations that the other does not. It may then be the case that with a subtle variation (one that predicts the same observations within experimental precision on the repository of past experiments) an "unorthodox" theory is suddenly isomorphic to yet another, possibly much simpler (that is, elegant), theory. The time has come then to start thinking of experiments for which the orthodox theory and the new one predict different outcomes. Some people seem to think that it is a waste of time to speculate on variations of orthodox QM since it has withstood all attempts at experimental falsification with an untarnished record. It seems extremely unlikely to me that this state will extend forever into the future. What is more important, new theories do not seem to spring forth from experimental falsification of old theories, but are dreamt up by original thinkers dissatisfied with the inelegance of those theories. For example, it is now known that Einstein was already (unsuccessfully) working on a theory of relativity before he knew of the Michelson-Morley experiments, driven by esthetic considerations. I find QM as it stands UGLY. This is not because I cannot "understand" it in terms of a macroscopic model with bouncing balls or jelly, but because it has a built-in *irreducible* casino, while we know now how little it takes to get chaotic behaviour as an emergent property from deterministic non-linear dynamic systems. I refuse to be convinced that there is not some (predictively almost identical) theory that does not suffer from this. And I do not mean ugly hacked variations of orthodox QM, but a conceptually truly different theory. One of the kind of things I am speculating about is that the world as observed is just a projection on a space of "observables" of the "true" world. I *know* that this is mathematically the same as introducing hideous variables and thus would be falsified because of Bell's inequalities. But maybe we are locked into a certain way of looking at all kinds of theories that causes these inequalities to be applicable, and are overlooking an obvious other kind in which an essential assumption in their proof does not hold. Unfortunately, I know too little of QM, QCD and what not to be able to speculate fruitfully about all this (and cannot find the time to take this subject seriously up), and, moreover, I am not Einstein. Still, I find thinking about this intellectually stimulating, and I for one have learned a lot more from the discussion in these newsgroups than from all kinds of popular books on QM combined. -- Lambert Meertens, CWI, Amsterdam; lambert@cwi.nl
turpin@ut-sally.UUCP (06/04/87)
In article <7407@boring.cwi.nl>, lambert@cwi.nl (Lambert Meertens) writes: > In article <5925@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) > replies: > > No. The "many-worlds" interpretation has been known for quite some > > time to make the same predictions as the Copenhagen interpretation. Well, no. When the Everett-DeWitt many-worlds interpretation was first proposed, the common view was that it was "merely" an alternate interpretation, and therefore instrumentally isomorphic with other interpretations. In recent years, some physicists have disputed this. In particular, David Deutsch, a young British physicist, has published several papers describing experiments that differentiate the many-worlds interpretation from the standard interpretation. See, for example: David Deutsch, "Three connections between Everett's interpretation and experiment," which appears as chapter 14 of Quantum Concepts in Space and Time, Clarendon Press, 1986, edited by Penrose and Isham. The supporters of MWI claim it is a purer quantum theory. In MWI, the change of a system through time can always be described by Schrodinger evolution. Under the standard interpretation, Schrodinger evolution is interrupted by periods of wave collapse. There is no universely accepted principle for determining when this wave collapse must occur, except it must take place after the last chance for wave interference and before human observation. The above book has several interesting chapters discussing quantum interpretations. Russell