ata comments on On Being Decoherent - Less Wrong

14 Post author: Eliezer_Yudkowsky 27 April 2008 04:59AM

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Comment author: ata 19 March 2011 07:58:31PM *  3 points [-]

MWI adds a preposterous amount of mechanism involving an infinite and ever-exponentially-expanding number of completely unobservable clone universes.

There's no mechanism to it other than the mechanism that every interpretation of QM already has for describing the evolution of non-macroscopic quantum systems. MWI just says that large systems and small systems aren't separate magisteria with different laws.

Also, MWI needs a way to determine when a "world" splits, or to shove the issue under the rug, every bit as much as collapse theories need to figure out or ignore when collapse occurs.

"Worlds" and "branching" are epiphenomenal concepts; they're simplifications of what MWI actually talks about (see Decoherence is Pointless).

Comment author: nick11 19 March 2011 09:38:08PM 0 points [-]

It doesn't matter whether branching occurs at a point of or at during some blob of time, probabilistic or otherwise, it's a central part of MWI and you need an equation to describe when it happens. And that equation should agree with the Born probabilities up to our observational limits. Likewise for collapse in theories that invoke collapse. Otherwise it's just hand-waving not science.

Comment author: nshepperd 20 March 2011 12:15:44AM *  4 points [-]

What is or is not a "branch" is unimportant. If you have read the link you'll know that a "branch" is not a point mass but a blob spread out in configuration space. All MWI needs is "the probability density of finding oneself in point x in the wavefunction is the amplitude squared at that point". It's standard probability theory then to integrate over a "branch" to find your probability of being in that branch. But the only reason to care about "branches" is because the world looks precisely identical to an observer at every point in that branch.