Dear Pat, (01)
> > Dear John,
> >
> >>
> >> MW> ... if I want to talk about 2 eyed sheep and 4 legged sheep
> >>> and determine if they are necessarily the same, then I need
> >>> only use sets that that go across all possible worlds.
> >>
> >> But those sets are purely imaginary.
> >
> > MW: Lewis would disagree with you. He claims that they are real
> and
> > not
> > imaginary, hence modal realism. This is really a feature of 4
> > dimensionalism though. In 3D only the present exists, and neither
> the
> > future or past do, whereas with 4D both the past and the future
> > exist as
> > well as the present. I am therefore not surprised that he chooses
> to
> > claim the possible worlds exist too. On the other hand I am
> > indifferent,
> > since it seems to me to make no difference.
>
> A point that might be relevant is that the 4D approach gives a
> natural
> account of what a possible world is. Lewis had to simply propose
> that
> they existed, a stance that was never widely popular, to put it
> mildly. But if we accept that 4D histories - spatiotemporal
> envelopes
> of events and physical existence - are real, and if, as seems very
> natural, we assume that they can stand in a relationship of
> containment to one another, ie have a mereology, and if we make a
> few
> very natural assumptions about this relationship, then one can show
> mathematically that there must be maximal elements in the space of
> 4D
> histories (maximal ideals in the order structure), and these play
> exactly the required role of possible worlds. So a possible world
> is
> simply a largest chunk of 4D space. Which is a very nice picture,
> seems to me. (02)
MW: Yes, I had worked that out too. I also like extend this to think of
branching worlds. So, for example, that all the possible worlds from
here have up to here as a part, and have different parts hereafter. That
gives another level of aggregation around all that is possible from here
(or wherever else you choose to branch from).
>
> Matthew, do you know if this has been developed by anyone and
> written
> up? I had meant to write it years ago, but never got around to it.
> If
> I havnt been gazumped yet, I might put it on the list of things to
> write when I retire. (03)
MW: I'm writing a book at the moment, and it will cover this to some
extent (I hope) but at a popular rather than academic level. Chris P is
the person to ask if it has already been written up properly somewhere.
He's read everything and is a sponge for this stuff. (04)
Chris, Can you give us chapter and verse? (05)
Regards (06)
Matthew West
Information Junction
Tel: +44 560 302 3685
Mobile: +44 750 3385279
matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx
http://www.informationjunction.co.uk/
http://www.matthew-west.org.uk/ (07)
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