Russell Standish wrote:
On Thu, May 14, 2015 at 01:04:09PM +1200, LizR wrote:
On 14 May 2015 at 12:32, Russell Standish <[email protected]> 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.
As I mentioned, a simple example is my decision between tea and coffee.
In
the MWI (or an infinite universe) there are separate branches (or
locations) in which I have both - but in the branch where I had tea, I
didn't have coffee, and vice versa. And because those branches can't
communicate, the road not taken remains counterfactual and non-physical
within each branch. Isn't that enough for the MGA to not need to worry
about counterfactuals, even in the MWI/Level whatever multiverse?
Why is communication needed?
Because otherwise there can be no physical influence, and - within the
branch(es) in which the MGA is being carried out - the recorded system is
identical to the non-recorded one. Without any physical communication /
interference there is no difference from a single universe version. Well,
ISTM, at least.
The "physical system" refers to all parallel instantiations of an
object ISTM.
If I refer to a photon travelling through a ZM apparatus (to fix
things - you know two half silvered mirrors, so the photons are split
and travel over two spatially disinct paths before being recombined),
we don't have two different physical systems in play. Its just
the one physical system, even though it occupies two distinct universes.
That is not the way the term 'worlds' or 'universes' is used in moder
quantum physics. The term 'world' is reserved for (related) systems that
have totally decohered, so that there is no possibility of
recombination. Or, in the cosmological setting, two regions of
space-time outside each other's Hubble volume.
The small number of people who still think that every possible path in
QM is a separate world form a fast-vanishing rump.
Bruce
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