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nick11 comments on On Being Decoherent - Less Wrong
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Then I can define a new hypothesis, call it objective collapse++, which is exactly your objective collapse hypothesis with the added assumption that objects cease to exist outside of our Hubble volume. Collapse++ has a slightly longer description length, but it has a greatly reduced runtime. If we care about runtime length, why would we not prefer Collapse++ over the original collapse hypothesis?
See my above comment about MWI having a fixed phase space that doesn't actually increase in size over time. The idea of an increasing number of parallel universes is incorrect.
BTW, it's MWI that adds extra postulates. In both MWI and collapse, parts of the wavefunction effectively disappear from the observable universe (or as MWI folks like to say "the world I find myself in.") MWI adds the extra and completely gratuitous postulate that this portion of the wave function magically re-appears in another, imaginary, completely unobservable "world", on top of the gratuitous extra postulate that these new worlds are magically created, and all of us magically cloned, such that the copy of myself I experience finds me in one "world" but not another. And all that just to explain why we observe a nondeterministic event, one random eigenstate out of the infinity of eigenstates derived from the wavefunction and operator, instead of observing all of them.
Why not just admit that quantum events are objectively nondeterministic and be done with it? What's so hard about that?
This does not correspond to the MWI as promulgated by Eliezer Yudkowsky, which is more like, "In MWI, parts of the wavefunction effectively disappear from the observable universe -- full stop." My understanding is that EY's view is that chunks of the wavefunction decohere from one another. The "worlds" of the MWI aren't something extra imposed on QM; they're just a useful metaphor for decoherence.
This leaves the Born probabilities totally unexplained. This is the major problem with EY's MWI, and has been fully acknowledged by him in posts made in years past. It's not unreasonable that you would be unaware of this, but until you've read EY's MWI posts, I think you'll be arguing past the other posters on LW.
Upvoted, although my understanding is that there is no difference between Eliezer's MWI and canonical MWI as originally presented by Everett. Am I mistaken?
Since I'm not familiar with Everett's original presentation, I don't know if you're mistaken. Certainly popular accounts of MWI do seem to talk about "worlds" as something extra on top of QM.
I think that's just a common misunderstanding most people have of MWI, unfortunately. Visualizing a giant decohering phase space is much harder than imagining parallel universes splitting off. I'm fairly certain that Eliezer's presentation of MWI is the standard one though (excepting his discussion of timeless physics perhaps).
Popular accounts written by journalists who don't really understand what they are talking about may treat "worlds" as something extra on top of QM, but after reading serious accounts of MWI by advocates for over two decades, I have yet to find any informed advocate who makes that mistake. I am positive that Everett did not make that mistake.
Mainstream philosophy of science claims to have explained the Born probabilities; Eliezer and some others here disagree with the explanations, but it's at least worth noting that the quoted claim is controversial among those who have thought deeply about the question.
Good to know.