On 10/26/2011 5:10 PM, Russell Standish wrote:
On Tue, Oct 25, 2011 at 04:00:56PM -0700, Nick Prince wrote:
QTI, Cul de sacs and differentiation

I’m trying to get a  picture of how David Deutsch’s idea of
differentiation works – especially in relation to QTI.  With a
standard treatment it looks as if there might be cul de sacs for  a
dying cat.  However I think I can see why this conclusion could be
wrong.  Maybe someone could check my reasoning for this and tell me if
there are any flaws.

I’ve entered this on both the FOR and the Everything list because I
hope it is relevant to both Forums.

I'm persona non grata on FOR, so must respond on the everything-list.

In section 8.1.3 of my book, I characterised David Deutsch's position
as a "single tracks through the multiverse". Namely that there is a
fact of which future history you will have (preordained as it were),
even if it is impossible to know it.

There has been quite a bit of discussion of "fungibility" recently,
and I'm now up to the section of BoI where David discusses this. I'm
inclined to think that the concept of fungibility really changes the
picture - namely one should think of the "single tracks through the
multiverse" as being fungible up until the point where they
differentiate. Being fungible, would entail the supervention of
consciousness on all fungible histories, and the full force of the QTI
conclusion. It would be interesting to hear (from David, or other
people) whether:

a) What David's position is now (are our futures determined or not?)
b) Was my characterisation of David's position was ever valid?
c) If so, and David's position has changed, what persuaded him to


I have just read the "Multiverse" chapter of "The Beginning of Infinity". It seems to me that Deutsch is just reinventing probability theory with different names "fungible" = "possible" and "multiverse" = "Borel sets". And he hasn't (up to where I have read) really solved the measure problem; he keeps giving examples which are simple binary alternatives.

I also wonder about his "sphere of differentiation". In Hilbert space there is no "sphere of differentiation"; entangled states are non-local. So is Deutsch using it as a just-so story, to be cleared up later?


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