On 12/10/2012 10:16 AM, Jason Resch wrote:
On Mon, Dec 10, 2012 at 10:30 AM, meekerdb <[email protected]
<mailto:[email protected]>> 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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