Re: many worlds interpretation

From: Mitchell Porter <>
Date: Sat, 21 Feb 1998 18:33:32 +1000 (EST)

> On Fri, Feb 20, 1998 at 09:16:12PM +1000, Mitchell Porter wrote:
> > But in that case 'world' can't be a fundamental concept, in the way
> > that many-worlds would have it. The essence of many-worlds, I thought,
> > was that *there are many worlds*, and we-here exist in one of them;
> > and the substance of the theory should lie in making these concepts
> > precise. But if the concept of world can't be given a crisp,
> > nonapproximate (i.e. nonarbitrary) definition, then I can't see
> > what use it has in this context.
> No, I think the essence of many-worlds is that there is no collapse, and
> that the UWF can be approximated as many worlds. The use, again, is as an
> intuition and computation aid. The problem with no collapse seems to be
> that the UWF quickly becomes very complex as it evolves. It's easier to
> think of it as a many independent, non-interfering worlds, even though
> that is only an approximation. In theory we don't really need the "world"
> concept. If we had enough computational resources we should be able to
> make predictions directly from the UWF without reference to worlds.
> Let me try to summarize MWI:
> 1. Physical reality is the UWF evolving according to the Schroedinger
> equation with no collapse.
> 2. The UWF can be approximated as many worlds.
> 3. If physical reality was many worlds, then we would expect to see what
> we see.
> 4. If physical reality was the UWF, then we would also expect to see what
> we see (because of 2 and 3).
> The reason we need "worlds" is to be able to derive 4, even though 1 and 4
> are what really matters, and they don't mention "worlds".

Aren't we-here supposed to be part of a world? But how can we
be part of an approximation? Is there no *exact* concept of 'world' about
which one can say, not just 'it's an approximation', but 'it's real'?

> > In that case, they won't affect each other at all, thanks to the
> > linearity of the Schroedinger equation. c_0 and c_1 will evolve
> > independently of each other.
> Yes, they evolve independently, but they still "affect" each other in the
> sense that they interfere (minimally) with each other. (BTW, I think you
> mean PSI_0 and PSI_1, since c_0 and c_1 are fixed coefficients.)

Yes, my last statement was a silly one, although true - they will "evolve"
by not changing! But in the specific case we are discussing, I don't see
how you can defend the claim that they affect each other. Your
mathematical criterion may possibly measure some form of correlation,
but that's a non-causal relation between worlds, and one having no
impact at all on their individual evolutions.

> I know there are some real experts on the MWI on this list. Please let me
> know if I'm on the right track.

Received on Sat Feb 21 1998 - 00:34:04 PST

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