On 06 Nov 2014, at 08:38, meekerdb wrote:
On 11/5/2014 9:26 AM, Bruno Marchal wrote:
On 04 Nov 2014, at 22:47, meekerdb wrote:
On 11/4/2014 9:23 AM, Bruno Marchal wrote:
On 02 Nov 2014, at 19:09, meekerdb wrote:
On 11/2/2014 1:27 AM, Bruno Marchal wrote:
On 01 Nov 2014, at 23:52, meekerdb wrote:
Are you aware of the Paul-Pavicic "bomb" detector?
http://cds.cern.ch/record/395858/files/9908023.pdf
I did not know this. Impressive.
It is most easily thought of as non-local in time.
I will have to think about that. If you can elaborate. I think
I intuit what you are saying, but well, I need to work more on
this.
Intuitively a photon is encouraged to enter the detector because
it is in resonance with an earlier instance of itself that is
already circulating in the detector. The experiment has not
actually been done; but I think it would not work if you
determined the time of emission of the photon to a precision on
the order of the circulation time in the detector.
Is this based on some (relativistic?) account of the energy-time
"uncertainty relation"?
I must confess I have some difficulty to grasp your explanation
but that might be due to my incompetence.
More likely a misfire of my intuition. I base it on their
analysis which just takes classical analysis of a continuous EM
wave of a single frequency (they note that a CW laser can have a
300Km coherence length so this is a good approximation). So the
solution is an EM field which is constant in time, modulo the
traveling phase. Then they interpret this as a probability
amplitude for a single photon. This implicitly makes the
probability amplitude for that single photon dependent on the wave
that is assumed to be time invariant. But then if you push the
quantum viewpoint further, that classical wave is just a
probability amplitude for photons that came earlier.
OK.
Of course like most quantum weirdness the weirdness comes from
assigning an interpretation that explicitly splits the wave and
particle pictures.
Is that not exactly what does the Copenhague dualisme, or von
Neumann projection? Hmmm ... ?
http://arxiv.org/pdf/1112.4522.pdf
No problem with that paper. As I am a bit skeptical about non-
locality, I am, like the author, certainly annoyed by the language
making people believing that there is some retro-causality involved
in delayed choice experiment.
I don't know why you should be bothered by that. The equations are
time symmetric and the direction of time is very likely just a
statistical feature; so if there are small reversals in isolated
systems that's just what one would expect.
OK. Actually, if the system is well isolated, we might be able to
reverse time completely. Bouncing back the computations, which are
reversible ... if really well isolated!
Now I will try, perhaps with my students, to get some "clearer"
many-world pictures of such non-locality in time.
Note that the usual Bell type of spatial non-locality is a non-
locality in time for any observer in motion with respect to Bob and
Alice. In the relativist frame, non-locality is always space-time
non-locality.
I just saw that Weinberg (in his "lectures on QM") seems to believe
that the MWI is automatically non-local, but I guess he points on
the MW theories which assumes some instantaneous split of the
entire universe. This of course makes no sense. The splitting, or
differentiation, goes at the interaction speeds. Superposition are
contagious, but not so much as becoming instantaneous. The
differentiation can't go faster than light.
I saw also that he attributes to Nicolas Gisin a theorem showing
that if we make the SWE slightly non linear, we get the possibility
of non local interaction between separated observers, that is,
instantaneous action at distance. He does not refer to its own
similar result. That Weinberg's book is very nice, if a bit short
on Bell, QC and foundations, (but then it is nice it refers to that
matter, don't avoid Everett, nor Bell, and there are other good
books on that topics (like Hirvensalo, for mathematicians, perhaps,
or the Gruska book, for Quantum Computation)).
I just read last week that Weinberg had tried various ways of
generalizing QM and he only found one that really worked and it
turned out to be a rediscovery of and operator form of classical
mechanics that had already been developed by Koopman and von
Neumann. KvN mechanics is essentially QM on phase space with the
assumption that all variables commute. I wonder if it would be a
good way to lead students into QM, assuming they were well grounded
in classical mechanics.
This assumes a lot. With quantum computation, you can get quickly
motivation for the QM axioms (even if people find this abstract, but
they can get quickly the essence of the quantum weirdness by working
on simple algorithm).
For classical mechanics, you have the complexity of analysis,
geometry, etc. classical mechanics is somehow harder than quantum
mechanics, well, for a logician.
You should look at how Vic Stenger gets QM in "The Comprehensible
Cosmos". I think you already have that book.
I read a lot of it in a bookshop, and a lot of papers by Stenger (but
I have only its book on God). What is Stenger position on QM. Collapse
or no collapse? I don't remember.
Bruno
Brent
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