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Aug20-09, 11:20 PM
Sci Advisor
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Quote Quote by apeiron View Post
Unlimited or boundless would be better terms in my book.

Regular notions of infinity would rely on the image of infinite extension - keep on adding forever. But I am thinking more in terms of the magic pudding - the infinitely divisible.
Except it's nothing like that. As I've been saying, nothing "new" is being created.

Quote Quote by apeiron View Post
Here I don't see how it is legitimate to treat a superposition as an actual macrostate. The superposition has to be decohered to be a definite something. A superposition is the before, not the after.
I think you're confusing the MWI interpretation with other interpretations that have wave function collapse. In the MWI, there is no collapse at all. There is only the appearance of collapse. The system is always in a superposition of many states. It's just that if certain interactions have occurred, then the different elements of the superposition cannot communicate effectively. That is all.

As for it not being legitimate to treat it as a macrostate in the thermodynamic sense, well, that's fine. A macrostate in thermodynamics is the set of macroscopic variables that are needed to fully-describe the macroscopic behavior of the system. Because different components of the wavefunction aren't observable in macroscopic systems, they don't belong in a consideration of thermodynamic macrostates. This doesn't mean that the MWI is wrong, just that the word "macrostate" is a poor word to use to describe the entire ensemble of configurations of the system.

Quote Quote by apeiron View Post
But the big QM issue here is the placing of the epistemic cut, the collapse of superposed states. And the MWI just ducks the issue by saying it never has to happen. There is no place the critical questions you mention actually get asked.
That's not ducking the issue. It's solving the problem of wavefunction collapse in an extraordinarily simple and elegant manner. And given the difficulty in demonstrating precisely how the appearance of collapse arises from the MWI, I would consider a claim that it's "ducking the issue" to be an admission of ignorance of the difficulties involved.

Quote Quote by apeiron View Post
Edit: Although the escape clause may be that, as you say, the presumption a lack of interference and so a quasi-separation of some kind. Yet this too must be vulnerable to the criticism it is unrealistic when it looks collapse does generally happen at quite small scales.
And at small scales you can actually calculate how effective the collapse should be, and therefore compare the prediction of the MWI against observation. So far observations match the predictions.