On Oct 8, 2009, at 2:24 PM, Chris Partridge wrote: (01)
> Pat, Matthew,
>
> I suspect that you two may know more than me in many areas - and it
> is quite
> a while - maybe 10 years - since I researched this in any depth.
>
>>> 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.
> Etc.
>
> What is interesting is how the branching links mereology and
> identity - and
> enables transworld objects.
> I think that one will need to deal with situations here where a
> temporal
> stage of person can be simpliciter part of several different people
> (their
> different futures) - but only a temporal stage of one person in one
> possible
> world/history. (02)
Right. There are some cases that have been discussed in (at least)
moral philosophy, involving identical twins, which at a very early
stage of fetal development, in some cases, were one blastula. If life
begins at conception, this is a difficulty. (See why I decided to
leave philosophy? :-) (03)
> One could also have several histories of a person (or whatever)
> where no
> part overlapped (as the divergence occurred before they were born).
> After a person ceased to exists, s/he would be part of ALL the
> subsequent
> diverging worlds.
> But maybe (like 4D) it is a case of getting used to the consequences
> of a
> position. (04)
There is a possibility much explored in science fiction, involving a
'matter transporter' which in fact disassembles its input, beams all
the needed information to the output device which then rebuilds an
exact replica; but then one of them goes wrong and leaves the original
intact, so 'the' person splits into two replicas. See 'Rogue Moon' by
Algys Budris, for example. (05)
>
> I also think that branching may have some uses, but not be a full
> replacement for the Lewis apparatus - as one might want a similarity
> where
> there is no (potential for) identity at any time in the past, so the
> histories never meet. (06)
The maximal ideal construction allows for this case. (07)
> Or, another example, how far back the divergence occurred may not be
> a good
> measure for how similar we want to say situations are. (08)
True, but in general, we should distinguish temporal alternativeness
from the alternativeness that gives rise to other modal notions. (09)
>
> For some references see
> http://plato.stanford.edu/entries/identity-transworld/ - '4.3
> Transworld
> identity and conditions for identity over time'- (cf. Brody, B., 1980,
> Identity and Essence, Princeton, NJ: Princeton University Press.,
> 114-15;
> 121 or Mills, E., 1991, "Forbes's Branching Conception of Possible
> Worlds",
> Analysis, 51: 48-50.)
>
> PH> Indeed, but (what I especially like) is that it gives many other
> ways
>> to 'branch', eg outwards spatially from a locally described
>> situation,
>> or backwards in the time-direction, when figuring out how something
>> that did happen could have happened.
>
> I believe that this is the way temporal logics often work (and some
> interpretations of physics - though this way out of my field). When
> I looked
> briefly, temporal logics used the metaphor of histories and
> branching, but I
> did not find any full-blooded 4D interpretation. (Pat am I right? I
> did not
> look very closely.) (010)
Well, I've not been reading actively for a while, but the last time I
looked, future-branching was the most common case. That gives you
Priors S4 logic, if its done straightforwardly. Certainly most of the
AI planning formalisms assume a fixed past (often starting with state-
zero). The most sophisticated case Ive seen has two independent Kripke
relations, one giving a linear tense and the other being a possibility
between entire world-lines. (011)
> But, to answer Pat's question, maybe there is room for a full-
> blooded 4D
> interpretation of branching. (012)
I think there is also a connection to the Barwise/Perry notion of
'situation', which is singular in that it is 'partial' compared to a
Kripke/Lewis possible world. Chunks of 4D seem to have this quality.
But this is all very vague at present. (013)
Pat (014)
>
> Regards,
> Chris Partridge
> Chief Ontologist
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>> -----Original Message-----
>> From: uom-ontology-std-bounces@xxxxxxxxxxxxxxxx [mailto:uom-ontology-std-
>> bounces@xxxxxxxxxxxxxxxx] On Behalf Of Pat Hayes
>> Sent: 08 October 2009 17:41
>> To: uom-ontology-std; Matthew West
>> Subject: Re: [uom-ontology-std] What is mass?
>>
>>
>> On Oct 8, 2009, at 2:49 AM, Matthew West wrote:
>>
>>> Dear Pat,
>>>
>>>>> 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.
>>>
>>> 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).
>>
>> Indeed, but (what I especially like) is that it gives many other ways
>> to 'branch', eg outwards spatially from a locally described
>> situation,
>> or backwards in the time-direction, when figuring out how something
>> that did happen could have happened.
>>
>>>>
>>>> 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.
>>>
>>> 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.
>>>
>>> Chris, Can you give us chapter and verse?
>>
>> I'd be grateful, yes.
>>
>> Pat
>>
>>>
>>> Regards
>>>
>>> Matthew West
>>> Information Junction
>>> Tel: +44 560 302 3685
>>> Mobile: +44 750 3385279
>>> matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx
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>>> http://www.matthew-west.org.uk/
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