On Wed, Sep 06, 2006 at 01:44:35PM -0700, "Hal Finney" wrote:
> 
> Russell Standish writes:
> > Why do you say this? Surely physical supervenience is simply
> > supervenience on some physical object. Physical objects are spread
> > across the multiverse, and are capable of reacting to all
> > counterfactuals presented to it.
> >
> > Inside views are local - but the whole shebang must be spread across
> > the Multiverse.
> 
> I suppose it depends on your definitions.  As I suggested, supervenience
> in a single world model means that consciousness depends on local physical
> activity, and not on causally unconnected events.  In a multiverse,
> actions in parallel worlds are causally unconnected to actions here.
> It seems rather odd to say that the supervenience thesis says that
> whether my computer is conscious depends on what is happening in some
> remote parallel universe.
> 
> I also think there are problems with this notion that objects are spread
> across the multiverse, and in particular that all counterfactuals
> are tested.  It's not clear to me that we can unambiguously define
> the counterpart to this particular object in an arbitrary multiverse.
> For very "near" or "similar" multiverses it may seem unproblematic,
> while for extremely "far" or "different" multiverses there will obviously
> be no counterparts.  There would probably be a gray area in the middle
> in which an object was related to one in our universe but perhaps not
> exactly the same.
> 
> This exposes a difficulty with the notion that all counterfactuals are
> tested.  In the first place, many thought experiments aim to refrain from
> testing counterfactuals - Maudlin's is of this nature.  Something has
> to go seriously wrong with Maudlin's scenario for counterfactuals to
> be tested.  In the second place, many counterfactuals may be bizarre
> and unlikely, so that the circumstances under which they are tested may
> require extremely strange events.  These situations would suggest that
> such counterfactuals will only be tested in relatively remote parts of
> the multiverse, parts quite different from our own.  And then we have
> to ask, is it really the "same" machine that is being tested?
> 
> And by "same" here, I think we mean more than just "designed the same"
> or "isomorphic" - we mean that it has some kind of shared identity,
> that in some sense this *is* the machine we see in our universe, just
> exposed to different inputs.  Given the problems I mentioned with this
> notion of identity across the multiverse, it's not clear that this
> concept makes sense.
> 
> Hal Finney

Take an object, say this coffee cup that is sitting on my desk in
front of me. It was created a few years ago in some vitreous furnace
in a factory. Ever since then, it has been a part of all those universes
that share the history of this coffee cup's creation (except of course
those in which the cup has been destroyed).

Sure there will be borderline cases - eg the cup smashed, but
strangely retaining the form of the cup and so on, but I would argue
that these borderline cases are of small measure relative to the
universes in which the cup exists or doesn't exist in an unproblematic
way.

This satisfies your shared identity requirement. It is more than
simply being isomorphic - it has shared history. All counterfactuals
*compatible with* that coffee cup's existence will be "experienced" by
the coffee cup.

All physical objects have this identity property across the Multiverse
(not covering the Multiverse, but occupying a non-zero measure slice
of it). We had this debate recently about whether persons could have
this identity property or not - with me being somewhat underwhelmed by
David Parfitt's arguments on this subject, but the situation is quite
clear with physical objects.

With physical supervenience, it is possible for the same person to
supervene on multiple physical objects. What is disallowed is multiple
persons to supervene on the same physical object.


-- 
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A/Prof Russell Standish                  Phone 0425 253119 (mobile)
Mathematics                              
UNSW SYDNEY 2052                         [EMAIL PROTECTED]             
Australia                                http://parallel.hpc.unsw.edu.au/rks
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