On 29/05/2017 10:42 pm, Telmo Menezes wrote:
On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
<bhkell...@optusnet.com.au> wrote:
On 29/05/2017 6:26 pm, Telmo Menezes wrote:
On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
<bhkell...@optusnet.com.au> wrote:
I would say that there is only one history leading to our present state.
Whether you take an MWI view or a collapse view, the wave function
branches
deterministically at every point, so if you follow your current twig back
down to the main trunk etc, there will be a unique path.
I don't think we can say we are in a specific twig. Many things about
out present state are unknown/undefined. I can imagine that there are
many well-defined present states that are compatible with my current
subjective state.
Sure, but we are talking about wave functions, not subjective states.
Replace "subjective" with "incomplete knowledge".
Doesn't help. Of course our knowledge is incomplete, the wave function
isn't completely known either -- but the result of specific measurements
are what is at stake here, and they are known quantum states.
In fact you can perform a quantum erasure experiment, and be sure that
your current state goes through at least two different shortest paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go into the
macroscopic world, but I don't see any reason to believe that it
doesn't.
I don't understand what you think you are getting in a quantum erasure
experiment. If the "which way" information that was gathered is erased,
normal interference patterns are seen in the double slit situation. The two
paths (through the separate slits) are in unresolved superposition until
they hit the detector, when decoherence takes over. There are not two
separate worlds, and your state is the result of the superposed paths, not
of either path separately. There is no ambiguity about which the the
"correct" path -- neither is, both contribute equally.
I would say that the delayed choice version of the experiment makes it
clear that there are two possible pasts that lead to the same present
state -- they differ by one bit of information.
That is not what is implied by delayed choice quantum erasure. Whether
an interference pattern is seen or not is determined by whether the
"which way" information is erased or not. But whether it is or not, the
interference is only seen when coincidence measurements tell one which
photons to count. And the timing information necessary for coincidence
determination is available only *after* all decisions about erasure or
not have been made, whether that decision is made before or after the
other photon of the entangled pair has reached its detector.
"Delayed choice" is perhaps a misleading phrase in this context, and it
does not lead to an ambiguity of path -- it merely tells whether there
was an intact superposition or not.
Bruce
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