Le 13-févr.-06, à 09:44, Hal Finney wrote (in part):

In many of our discussions of multiverse models, we have explicitly or
implicitly included the notion of measure, that some universes would be
more "common" or more "prominent" than others.  This is often linked to
extensions of Occam's Razor, so that universes with relatively simple
models would have higher measure than those that are more complex.

The necessity of "simplicity" could perhaps be a consequence of comp, but this remains to be shown. But even if that is the case, I don't see how "simplicity" would make the model having a higher measure, unless you attach consciousness to particular individuals in particular universe, but this can be done only by identifying the first person and some arbitrary particular third person description. And the UDA shows this cannot be done (with comp).

Physics is a science, and that means it needs to work with theories that
can be tested and disproven.  We are a long way from being able to come
up with any experiment that a working physicist in his lab could run
to see whether multiverse models are correct.  (And no, quantum suicide
doesn't count!)

The day physicists will understand the logician's sense of model and theories, things will be pretty much clear. If we agree that physicists obey the same laws as the particles they describe, then, even just the two slits experiment entails mutiverses, and confirms QM which is literally a mutiverse theory (even with the collapse, which is just an invention for cutting on the typical quantum contagion of the superpositions). Also, note that the 0-universe, 1-universe, infinity-of-universes are all on the same par. Nobody has ever tested the existence of a primitive physical universe nor of the existence of Aristotelian Prime Matter, and other common sense idea on which those physicalist ideas derive. Note also that the theory of Matter given by the loebian (introspective) machine is 100% testable.

I also get the impression that Susskind's attempts to bring "disreputable"
multiverse models into "holy" string theory is more likely to kill
string theory than to rehabilitate multiverses.

String theory relies entirely on QM and so inherits all its interpretation problems. Except that in String Theory, like Quantum Cosmology, the "wave collapse" is still more unintelligible. Witten makes the points in a conference some years ago. According to him String Theory is still very fuzzy on the whole wave aspect of strings, above its traditional role as computation tool.

 Perhaps I am getting a
biased view by only reading this one blog, which opposes string theory,
but it seems that more and more people are saying that the emperor has
no clothes.  If string theory needs a multiverse then it is even less
likely to ever be able to make physical predictions, and its prospects
are even worse than had been thought. A lot of people seem to be piling
on and saying that it is time for physics to explore alternative ideas.
The hostile NY Times book review is just one example.

To be sure I disagree that string theory is not testable, and I think the multiverse idea is testable and already indirectly tested and that it is the most certain consequence of QM. Now, as a theory of everything, string theories, like QM and actually the whole physics enterprise, are flawed at the start, because those approach relies (consciously or not) on a hardly clear or coherent theology inherited mainly from Aristotle, and which tends to put the mind-body problem under the rug.



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