# Re: How does this probability thing work in MWI?

From: Fritz Griffith <fritzgriffith.domain.name.hidden>
Date: Wed, 17 Nov 1999 06:14:19 MST

It seems to me that the 'alternate degrees of reality' interpretation and
the SSA interpretation both have differing implications. I have a hard time
with the SSA, for the following reason, which I've already mentioned:

for every split in which we are favored to follow a certain world, there
exists another world of equally real people who assumed they would follow
the same path, who instead ended up in the so-called unlikely world.
Because the people in both worlds are equally real, there is no way to say
that we are more likely to follow either path; rather, between this
single-split example, the chance would be 50/50 as to which world we would
end up in. It would be arrogant to assume that we would have to be the
people in the more probable world. Considering all possible worlds, we are
back to the drawing board - the chance of us actually being in a world that
isn't chaotic is pretty much nonexistant.

Let me know if and why this doesn't make sense.

>From: Russell Standish <R.Standish.domain.name.hidden>
>To: fritzgriffith.domain.name.hidden (Fritz Griffith)
>CC: R.Standish.domain.name.hidden
>Subject: Re: How does this probability thing work in MWI?
>Date: Wed, 17 Nov 1999 16:33:27 +1100 (EST)
>
> >
> > I understand that each world's probability is well defined by QM. What
>I
> > don't understand is how that probability can be implemented into the
>MWI.
> > Would you say that only one world can exist, and it is chosen from the
> > probabilistic equations of QM? Or does each world exist to a certain
> > degree, some more than others, as described by the equations of QM (what
> > Chris was saying)? Or, does every world exist, just as much as every
>other,
> > but the equations of QM determine which world we will end up in? Or, is
>it
>
>The last way of putting it is probably the best way to look at
>it. This also corresponds to the Self Sampling Assumption. The first
>way you put it definitely corresponds to the Copenhagen
>interpretation. The way Chris put it is something I'm comfortable
>with, as I do tend to use the notion of differing degrees of reality,
>and this notion corresponds fairly closely with the likelihood of that
>outcome, however putting it in terms of the SSA is the least problematic.
>
> > something else entirely?
> > This is where I am confused, because I have heard that all worlds are
> > equally real, I have heard that only one really exists, and now Chris is
> > telling me that there are different degrees of reality to all of these
> > worlds. And now I'm very confused.
> >
> >
> > >From: Russell Standish <R.Standish.domain.name.hidden>
> > >To: fritzgriffith.domain.name.hidden (Fritz Griffith)
> > >CC: everything-list.domain.name.hidden
> > >Subject: Re: How does this probability thing work in MWI?
> > >Date: Wed, 17 Nov 1999 15:30:34 +1100 (EST)
> > >
> > >Now hang on - every world does have a measure associated with it. A
> > >world will correspond to a particular eigenvector \psi_w of some
> > >composite observable operator W. The measure of that world (relative
> > >to the whole multiverse) is given by the 'overlap integral'
> > ><\psi_w|\psi>/<\psi|\psi>, where \psi is the Multiverse state vector.
> > >
> > >All of this is well defined within QM.
> > >
> > >Now you could state that this measure corresponds to different levels
> > >of reality, but that is simply a matter of taste or
> > >definition. However, what is true, is that this measure imposes
> > >structure of the multiverse so that the descent into chaos doesn't
> > >happen. It seems that this is what Chris was saying all along, but it
> > >appeared to have zipped right on by.
> > >
> > > >
> > > > Now this is where the MWI starts losing its appeal. This
>'unequal
> > > > reality' is very similar to the Copenhagen 'ghost states' that the
>MWI
> > >was
>reality
> > >stuff
> > > > just speculation, or is it the actual explanation?
> > > > The only way your unequal reality idea could be the actual
> > >explanation is
> > > > if reality was defined by, as you say, a third party observer, who
>could
> > > > observe all worlds at the same time. This third party observer
>would be
> > > > quantum mechanics. So you are suggesting that there are different
> > >degrees
> > > > of reality, and that how real something is is independent of how
>real we
> > > > percieve it to be. Perhaps it is true, but nevertheless it is a
>very
> > >shaky
> > > > argument. At the very least, it is a weakness of MWI because of its
> > >vague
> > > > and confusing statements.
> > > > On the other hand, if you assume that every world is either real
>or
> > >not
> > > > real, then you either have the Copenhagen view, or you must accept
>that
> > > > every possible world is real. With the latter view, I have already
> > >shown
> > > > that order is impossible:
> > > >
> > > > <snip>
> > > > for every split in which we are favored to follow a certain world,
>there
> > > > exists another world of equally real people who assumed they would
>they
> > > > would follow the same path, who instead ended up in the so-called
> > >unlikely
> > > > world. Because the people in both worlds are equally real, there is
>no
> > >way
> > > > to say that we are more likely to follow either path; rather,
>between
> > >this
> > > > single-split example, the chance would be 50/50 as to which world we
> > >would
> > > > end up in. Considering all possible worlds, we are back to the
>drawing
> > > > board - the chance of us actually being in a world that isn't
>chaotic is
> > > > pretty much nonexistant.
> > > > <snip>
> > > >
> > > > So, we have two options: either accept your 'varying degrees of
>reality'
> > > > theory, or go back to the Copenhagen view (or, another option is to
> > >consider
> > > > the theory in my post, "Why the Wave Function Theory Doesn't Make
> > >Sense").
> > > >
> > > >
> > > >
> > > > >From: Christopher Maloney <dude.domain.name.hidden>
> > > > >To: everything-list <everything-list.domain.name.hidden>, Fritz
>Griffith
> > > > ><fritzgriffith.domain.name.hidden>
> > > > >Subject: Re: How does this probability thing work in MWI?
> > > > >Date: Mon, 15 Nov 1999 21:45:06 -0500
> > > > >
> > > > >Fritz Griffith wrote:
> > > > > >
> > > > > > So if MWI is just a mathematical interpretation of QM, then why,
>in
> > > > >every
> > > > > > article I read about MWI, does it say that every world is
>equally
> > >real?
> > > > > > Could they all be wrong? Also, if every world is not equally
>real,
> > >then
> > > > > > wouldn't you basically have the Copenhagen view of QM?
> > > > >
> > > > >This is a good point, I think. Perhaps "equally real" is
> > > > >If the measure of two histories is unequal, perhaps one should say
> > > > >that they are unequally real -- one is more real than another.
> > > > >Actually, this is reminiscent of a discussion I had with Jacques
> > > > >Mallah a while back about zombies. I don't believe that such a
> > > > >thing as a zombie exists (something that looks and behaves like a
> > > > >conscious human, but is not conscious) but I do believe that it is
> > > > >probably valid to talk about some people as having a greater
>measure
> > > > >than others -- that is, that some people are more real than others.
> > > > >
> > > > >There's a significant difference, I think, between saying that
> > > > >something is "less real" and saying that something is "not real".
> > > > >Certainly, to those people of low measure, they themselves *feel*
> > > > >themselves to be just as real as anyone else. But the measure
> > > > >question comes up from a third person perspective (or "bird"
> > > > >perspective, or "Archimedes" perspective): how likely is it that
> > > > >a self-aware observer will find him/herself to be that person?
> > > > >
> > > > >So, to make a long story short, I think confusion can arise from
> > > > >the use of the word "real", whether one means it to be a boolean
> > > > >on/off state, or something that can be measured by a continuum. If
> > > > >one is using it as a boolean, then one would say that alternative
> > > > >histories of MWI are all equally real, meaning that they all are
> > > > >real, just as ours are. But they are not all equally probable.
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > > >From: Christopher Maloney <dude.domain.name.hidden>
> > > > > > >
> > > > > > >In this and your previous post, I think you are confusing the
>MWI
> > >with
> > > > > > >a *theory*. The MWI is not a theory, it is an *Interpretation*
>of
> > >the
> > > > > > >theory of Quantum Mechanics. QM defines the math and therefore
>the
> > > > > > >measure which is manifested by the MWI.
> > > > > > >
> > > > > > >On the other hand, your questions about measure certainly do
>apply
> > >to
> > > > > > >the theory discussed on this list, the All-Universes Hypothesis
> > >(AUH).
> > > > > > >With the AUH, we need to justify the measure of the alternative
> > >worlds,
> > > > > > >in order to make predictions for observations. The AUH is not
> > > > > > >equivalent to the MWI. It is a sort of super-many-worlds idea,
>but
> > >it
> > > > > > >doesn't presuppose quantum mechanics, as MWI does. In fact,
> > >ideally
> > > > > > >we would be able to derive QM from the AUH. In fact, Russell
> > >Standish
> > > > > > >purports to have done that in his just pre-released paper, at
> > > > > > >http://parallel.hpc.unsw.edu.au/rks/docs/occam/.
> > > > > > >
> > > > > > >
> > > > >
> > > > >
> > > > >--
> > > > >Chris Maloney
> > > > >http://www.chrismaloney.com
> > > > >
> > > > >"Donuts are so sweet and tasty."
> > > > >-- Homer Simpson
> > > >
> > > > ______________________________________________________
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> > > >
> > > >
> > >
> > >
> > >
> >
> >----------------------------------------------------------------------------
> > >Dr. Russell Standish Director
> > >High Performance Computing Support Unit,
> > >University of NSW Phone 9385 6967
> > >Sydney 2052 Fax 9385 6965
> > >Australia R.Standish.domain.name.hidden
> > >Room 2075, Red Centre http://parallel.hpc.unsw.edu.au/rks
> >
> >----------------------------------------------------------------------------
> >
> > ______________________________________________________
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> >
>
>
>
>----------------------------------------------------------------------------
>Dr. Russell Standish Director
>High Performance Computing Support Unit,
>University of NSW Phone 9385 6967
>Sydney 2052 Fax 9385 6965
>Australia R.Standish.domain.name.hidden
>Room 2075, Red Centre http://parallel.hpc.unsw.edu.au/rks
>----------------------------------------------------------------------------

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Received on Wed Nov 17 1999 - 05:16:52 PST

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