Fred Chen wrote: >The MWI of quantum mechanics (where worlds share common laws and >characteristics) and the multiverse concept from Tegmark, Schmidhuber, Lewis >and others ...

An inattentive reading of some of my posts could give the idea that I (Bruno) belong among the others. To prevent misunderstanding let me make precise that *in some sense* (explained below) I am closer to Everett/Deutsch/qm-MWI than Tegmark, Schmidhuber, Lewis. (Although nuances could be added but I prefer to remain short). >... (all logically possible universes exist, including those with >different laws and characteristics) I believe, like David Deutsch says, that "all logically possible universe" is a quasi-contradictory notion. To give a reasonable semantics of *that* "all", you need something bigger ... In the comp approach, the "everything" is the running of all programs, (which *can* be defined mathematically, and is universal in a sense deepened by Church Thesis). The laws of physics are eventually derived from average possible consistent point of views, and made *necessary*, The very idea of a "physical universe with other laws" is just meaningless. But then any notion of even one universe/multiverse, is given a phenomenological derivation, without the need to postulate one. >are very similar, but they are actually >independent concepts. It is an interesting perspective you bring up where >all possible universes could actually be MWI-type splittings of a computer >running a program. This is common in Schmidhuber and me. But Schmidhuber, to sum up crudely is like a sort of Bohmian Computationalist, in the sense that Juergen attachs the "private mind" of the observer to a single computation, and this just doesn't work with the comp hypothesis, once we take account of the first and third person (and other point of view nuances) differences. Of course DD postulate a uni/multiverse from a theory (QM) which is partly empirically infered. I infer only the arithmetical truth, but I give an explanation why sound machines believe in universe(s). I show that comp leads to idealism (UDA). No problem abandoning comp at that point. But I don't see a contradiction. Quite the contrary when I translate the UDA in ``the sound machine language", thank to the work of Godel, Lob, Solovay,(+ Boolos, Goldblatt, Visser, ...) I got quantum logic for the description of ``probability 1" on the UD* indeterminacy domain, so the QM confirms a posteriori comp. Bruno