meekerdb wrote:
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 <li...@hpcoders.com.au>
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."
If you read around the typos in my post above, the counterfactual
if...then...else... construction branches on the input A, which is not
necessarily *anything* at all, just what the program encounters. It is B
and C that can be anything that the programmer wants them to be. We are
talking computing here, not physics. That is why the other worlds of MWI
have nothing to do with counterfactual correctness.
Bruce
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