On 14 May 2015, at 06:51, Bruce Kellett wrote:
Russell Standish wrote:
On Wed, May 13, 2015 at 10:33:42PM +1000, Bruce Kellett wrote:
Bruno Marchal wrote:
On 13 May 2015, at 08:20, Russell Standish wrote:
For a
robust ontology, counterfactuals are physically instantiated,
therefore the MGA is invalid.
I don't see this. The "if A then B else C" can be realized in a
newtonian universe, indeed in the game of life or c++.
And the duplication of universe, one where A is realized, and B
is realized
+ one in which A is not realized and C is realized,
might NOT makes a non counterfactually correct version of that
if-then-else suddenly counterfactually correct.
Counterfactuals and MWI (and robustnesse) are a priori
independent notions.
For once I agree with Bruno. I think this is right and that
counterfactuals are not, as Russell suggests, instantiated in the
other worlds of the MWI in any useful sense.
How does that work? Are you saying the counterfactual situations
never
appear anywhere in the Multiverse? What principle prevents their
occurrance?
By the meaning of the term: *counter*factual, i.e., contrary to the
facts of the situation. As far as I know there is a philosophical
theory of counterfactuals based on possible worlds.
Yes. The study of counterfualness often use modal logic, and is often
considered as a modal notion. The problem here relies in part in the
fact that logicians, physicists, and philosophers use the same words
with different meaning, and here we need to unify the ideas, so it is
easy to get confused.
But these are generally though to be imaginary. And my feeling is
that the 'other worlds' of the MWI or other Hubble volumes, etc, are
just philosophical possible other worlds. We can say anything about
them that we like because it can never be checked -- they are
physically inaccessible in principle.
But with comp, that is not enough. Even if a physically existing, but
non accessible physical reality realize a computation similar to a
continuation of you, it might change the measure, in principle.
But we are always going to have difficulty assigning a truth value
to a counterfactual like: "The present king of France has a beard."
It will indeed depends on the interpretations. But if you say it is a
counterfactual, it should have the form: "if there is a king of
France, then he has a beard". It is "trivially" true in classical
logic (assuming France is really a republic), but classical logic is
not suited for counterfactuals, by definition, they are all true: if
pigs can fly, I am Napoleon!", for example. False implies everything
in classical logic. For counterfactuals, you need special classical
modal logic(s), or sort or relevance logics.
Bruno
Bruce
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