On 12/10/2012 10:16 AM, Jason Resch wrote:



On Mon, Dec 10, 2012 at 10:30 AM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    On 12/10/2012 2:56 AM, Bruno Marchal wrote:
    But why isn't "It's a probabilistic world and it obeys the Born rule." a 
good
explanation. I'm all for finding a better explanation, i.e. a deterministic one. But simply postulating an ensemble of worlds to make the probabilities
    "deterministic" in arbitrary way doesn't strike me as any improvement.

    It is, as it explains interference, without adding something not well 
defined
    (apparatus, observer) not obeying QM (like with the collapse needed to get 
one
    physical reality).

    That sounds like prejudice against probabilistic theories.  The 
interference is
    inherent in the complex Hilbert space states.  The interference happens in 
one
    world.  As Omnes says, you don't need 'collapse' you just need to accept 
that you
    have calculated probabilities.  That's what probability means - some state 
is
    actualized and others aren't.


How does Omnes explain the EPR experiment without collapse? It seems you need to give up not only determinism, but also locality.

Also, what do you think Omnes would predict as the outcome for Deutsch's proposed experiment:

    In Deutsch's thought experiment, an atom, which has a determinate spin 
state in one
    axis, 'left' for example, is passed through a Stern-Gerlach apparatus which 
has the
    possibility of measuring it in another axis, as either spin 'up' or spin 
'down' in
    this case. This means that the atom is then in a superposition of 'up' and 
'down'
    states from the perspective of an observer who has not yet become entangled 
with it.
    This superposition travels to the AI's artificial 'sense organ'. Here it is 
provided
    with two options, it may be detected as either spin 'up' or spin 'down'. 
The AI's
    conscious mind then records the result. The collapse approach predicts that 
this
    will cause the atom to collapse into one determinate state, with either a
    determinate 'up' or 'down' (but not 'left' or 'right') spin. The Everett 
approach
    predicts that the mind will branch into two, one mind will record up and 
one down
    (but neither will record 'left' or 'right').

    The whole process is then reversed so that the atom emerges from the 
entrance to the
    Stern-Gerlach apparatus and the mind forgets which result it recorded. This 
process
    does not erase any of the AI's other memories however, including the memory 
that
    they did record the atom to be in a definite state. If a 'left-right' 
detector was
    placed at the entrance of the Stern-Gerlach apparatus then the collapse 
approach
    predicts that it will be detected as being in either a 'left' or 'right' 
state with
    equal probability.


I think it is wrong in saying that the erasure of which-way information (which I think is actually impossible for a consciousness, artificial or otherwise) will leave the atom in an up/down state. You keep asking me about 'collapse', but Copenhagen's physical collapse is not the same as Omnes epistemic collapse.

Brent

    If the Everett approach is correct then the atom will be in the same state 
that it
    was in before the measurement, it will still have a 'left' spin.

      --- http://www.thestargarden.co.uk/EvidenceOfParallelWorlds.html


Jason
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