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From: Wei Dai <weidai.domain.name.hidden>

Date: Tue, 20 Jan 1998 13:10:11 -0800

On Tue, Jan 20, 1998 at 10:14:24AM -0800, Robin Hanson wrote:

*> I need to get back to even more basic basics.
*

*>
*

*> 1) There's a certain elegant simplicity to the claim "all possible universes
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*> exist", at least if "possible" is interpreted as broadly as possible, i.e.,
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*> "not logically inconsistent". But if you start substituting other meanings
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*> for "possible", I think the elegance quickly disappears. You'd then still
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*> have to explain why other non-logically-inconsistent universes don't exist,
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*> and you'd have a bunch more weird universes to explain why we don't easily
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*> observe them.
*

The problem is coming up with a definition of "possible" that actually

leads to a useful theory. Otherwise we're left with "All possible

universes exist, so what?" I think the set of all Turing machines is

broad enough and simple enough to be considerably more elegant than

assuming that only one specific universe exists. It's not a problem to

explain why we don't observe other universes. This is simply because TMs

are independent of each other. I agree that it would be nice to either

have a broader useful definition of "possible" or a strong justification

of why non-computable universes do not exist, but I don't think it is

necessary.

*> I find the many worlds theory of quantum mechanics elegant, but not because
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*> it can be thought of as equally the above claim with a certain odd quantum
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*> definition of "possible". I find it elegant because it seems simpler than
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*> the known alternatives which account for the empirical data.
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*>
*

*> 2) I can see why you might want some sort of prior over universes, so you
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*> can make inferences about what universe you are in. But why should your
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*> difficulty in choosing such a prior be an argument against universes
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*> existing? Just because you have trouble thinking about a universe doesn't
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*> mean it doesn't exist.
*

I think one of the main reasons for considering the idea that all possible

universes exist is to establish a rigorious basis for induction, and for

that we need a prior over universes.

*> 3) My basic problem with the "all possible universes exist" claim is that
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*> I find it hard to figure out whether my actions have any consequences.
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*> If all possible universes exist, then for any me in one universe choosing
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*> one action, there is another me in another universe choosing another action.
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*> In a global sense I can't choose actions anymore. All possible actions get
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*> chosen.
*

But isn't this also a problem with the many-worlds interpretation of

quantum mechanics? I'm not sure what the solution is but I assume there is

one, since the many-worlds interpretation seems to be fairly widely

accepted.

Received on Tue Jan 20 1998 - 13:11:03 PST

Date: Tue, 20 Jan 1998 13:10:11 -0800

On Tue, Jan 20, 1998 at 10:14:24AM -0800, Robin Hanson wrote:

The problem is coming up with a definition of "possible" that actually

leads to a useful theory. Otherwise we're left with "All possible

universes exist, so what?" I think the set of all Turing machines is

broad enough and simple enough to be considerably more elegant than

assuming that only one specific universe exists. It's not a problem to

explain why we don't observe other universes. This is simply because TMs

are independent of each other. I agree that it would be nice to either

have a broader useful definition of "possible" or a strong justification

of why non-computable universes do not exist, but I don't think it is

necessary.

I think one of the main reasons for considering the idea that all possible

universes exist is to establish a rigorious basis for induction, and for

that we need a prior over universes.

But isn't this also a problem with the many-worlds interpretation of

quantum mechanics? I'm not sure what the solution is but I assume there is

one, since the many-worlds interpretation seems to be fairly widely

accepted.

Received on Tue Jan 20 1998 - 13:11:03 PST

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