On 5/13/2015 10:25 PM, Bruce Kellett wrote:
meekerdb wrote:
On 5/13/2015 5:32 PM, Russell Standish wrote:
On Thu, May 14, 2015 at 11:26:17AM +1200, LizR wrote:
On 13 May 2015 at 18:20, Russell Standish <[email protected]> wrote:
For a robust ontology, counterfactuals are physically instantiated,
therefore the MGA is invalid.
Can you elaborate on this? ISTM that counterfactuals aren't, and indeed
can't, be physically instantiated. (Isn't that what being counterfactual
means?!)
No - counterfactual just means not in this universe. If its not in any
universe, then its not just counterfactual, but actually illogical, or
impossible, or something.
If "not in any universe" is meant in the Kripke sense, then something not in any
universe is something that is logically impossible. But if "not in any universe" is
meant in the MWI sense, then counterfactuals are only those outcomes consistent with QM
but which don't happen. I think it is only the latter kind of counterfactual that need
be considered in computations.
No. The counterfactuals that Bruno refers to in comp seem to come from the "If A the B
else C" construction of computer programming. This puts no restriction on the worlds
containg B and C.
That would seem to create conundrums. The counterfactual is A taking a value other than
the one it actually did. A is one of the inputs to the prosthetic brain part, so in
practice the doctor would only consider a finite number of values of A that could be
realized by the sense organ or other brain parts that realize it. But if A can be anything
from platonia it could be "If this program X halts..." or "The smallest even integer not
the sum of two primes."
Brent
So it actually has nothing whatsoever to do with MWI. As you say, the possible
alternative worlds in MWI come from the eigenfunctions of an eigenselected basis, and
those are by no means arbitrary.
Bruce
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