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| The Afshar Experiment: Farewell to Copenhagen? |
Posted by Karl on Tuesday April 27, @01:43PM
from the dept.
As reported on Kathryn Cramer's blog, physicist Shahriar S. Afshar, a Visiting Scientist at Harvard University's Physics Department will give a talk tonight entitled Violation of Bohr's principle of complementarity in an optical "which-way" experiment at Texas A&M University.
This experiment appears to be a confirmation of Kathryn's father, John Cramer's Transactional interpretation of quantum mechanics. The Transactional interpretation resolves all of the paradoxes of the Copenhagen interpetation--i.e. Schroedinger's cat, Uncertainty, nonlocality, etc. It does so by positing that events at the quantum level propagate influences both forward and backwards in time.
I met John Cramer a month ago in Boston and we talked about his interpretation. I've always been fond of the Copenhagen interpretation, because it's a nicely post-modern approach to reality. John's interpretation doesn't deny any of the quantum strangeness that goes on in the world, but it does call into question the value of Bohr's principle of complementarity, at least as applied to quantum mechanics.
More importantly, Afshar's experiment not only falsifies the Copenhagen interpretation, it also falsifies the Many-Worlds interpretation (whew!) and possibly other interpretions as well.
So some determinism is leaking back into our view of the world. It does so, however, by stressing the physical reality of nonlocality, especially temporal nonlocality: all events are connected, both in space and in time. (For instnace, you can use gravitational lensing of 14 billion year old starlight around intervening galaxies to perform a double-slit experiment, and under the Copenhagen interpretation this means that you, the experimenter, are deciding whether a photon was emitted as a particle or wave 14 billion years ago; in John's interpretation, you are actually communicating with the source of the photon, back through time 14 billion years. So the Transactional interpretation is still mind-boggling, and we're not going back to the naive realism of Newton's day. But neither can we any longer fill quantum mechanics with any amount of mystical crap by appealing to Bohr's paradoxes.
A shame, in a way. I had a soft spot for some of that mystical claptrap.
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Re: The Afshar Experiment: Farewell to Copenhagen?
by Becky Afshar on Wednesday May 26, @10:43PM
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Have you ever stopped to think that you might be the "MCA" Karl?
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Re: The Afshar Experiment: Farewell to Copenhagen?
by Alberto Mancini on Wednesday May 26, @10:47PM
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Karl, why don't you visit this website: http://groups.msn.com/ThePhilosophyCafe and post your opinion in there.
Becky, are you Sarah Afshar's sister? If so, are you related to Shah? It's nice to see the family support.
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Re: The Afshar Experiment: Farewell to Copenhagen?
by Aletheian Institute on Friday May 28, @01:45PM
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Fascinating. I had actually been working with a version of the Many-Worlds interpretation which takes into account nonlocality in order to unify the various multiverse levels (as suggested by Tegmark), and that was fun, but I've always had a fancy for the Transactional Interpretation. I wouldn't mind having my work with the Everett idea turn out to be claptrap if the TI were true. It is a wonderfully dialectical interpretation in terms of including both forward-time and backward-time solutions for the Schroedinger equation. The TI always struck me as a more complete interpretation, and despite its preservation of quantum weirdness, it always seemed somehow more plausible that the magical thinking of Copenhagen.
Attached is my paper on quantum mechanics, which has nothing to do with this article, but could be fun for Everett fans.
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Re: The Afshar Experiment: Farewell to Copenhagen
by z on Wednesday August 11, @02:54PM
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Quantum Mechanics
The way I see quantum mechanics is this. The properties (energy, charge, field, etc) of the quantum system are distributed over all the states defined and described by the wave function. I believe that this is a continuous distribution, with actual quantum or sub-quantum connectlvity between the eigenstates. This implies a completely continuous wave function. When an interaction ( of sufficient strength and asymmetry) occurs, a localization of the property distribution of the system takes place and the wave function appears to collapse. This apparent collapse is just a reorganization of the property distribution of the system, due to the exact nature of the interaction. Since we due not Know the exact nature of the interaction, it appears probabilistic, but is actually totally determined, within the limits of the uncertainty principle.
As an example, consider a quantum system that can described as being in state A or B with equal probability. This would mean that the properties of the system are equally distributed over states A and B, with a very small amount constituting the state corresponding to the connectivity. When this interacts with another non-quantum (already localized) system whose exact structure is unknown, then there is a 50/50 chance for the localization of the original system to occur in either state A or B. If the quantum properties of the second system are non- localized and known, localization probabilities for the first system will be different.
In the double slit;it experiment, the probabilities are totally dependent on the photon's property distribution at the point of interaction with the screen, since the exact structure of the screen is unknown and it presents an equal opportunity for interaction with the various portions of the photon state distribution.
In this view, there is no abrupt collapse of the wave function. There is just a continuous change in the wave function due to the localization and de-localization of the property distribution of the systems involved.
Entanglement implies a partial or complete overlap of the property distribution and/or the connectivity distribution. It could also imply a secondary connectivity distribution.
In the double slit experiment the photon always goes through both slits (properties distributed in a two state form).The property distribution then takes on the normal (interference} density form as the two state form expands from the slits.. This always disallows a which-way determination since it does not exist.
Reality and QM
Reality is not necessarily imprecise or fuzzy. We use mathematical and conceptual models to understand our experiences. If, in light of these models, reality appears imprecisely defined or fuzzy or probabalistic, it cannot readily be said that reality itself is as such. The models that we use, and our understanding of the mapping between reality and the models, are what introduce such imprecision and fuzzyness to our understanding of said reality.
All we can really say is that the models are good enough to explain, in an adequate manner, our experiences, and to produce technologies that work.
Quantum theoretical limits on measurement and prediction are not necessarily based in the nature of reality, but in the structure of our models of reality.
Afshar experiment
Since the experiment has demonstrated, albeit indirectly, that interfernce is taking place during the experiment, then this implies that the wavefunction at each detector MUST contain components from both slits.
If it did not contain components from both slits, then you could not have demonstrated interference.
The wavefunction at the detectors is just the spacially extended wavefunction that provides for the indirect evidence of interference.
The focusing lenses return the wavefunction to a two state condition with each state containing elements from each (both) of the two slits.
The detectors then have a 50/50 chance of recording the photon.
This is similar to what happens in a Rydberg atom when pumped up to a large superposition. The decay of the superposition often results in a two state function before settling into its final state.
It is also possible that the wavefunction is completely reduced to a single state at the focusing lenses. This however, does not change the fact that elements of both slits are contained in the wavefuntion before its localization and NO amount of conceptual argument will change the fact that the detector CAN NOT unambiguously determine the which-way information.
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Re: The Afshar Experiment: Farewell to Copenhagen?
by Mark Recney on Tuesday February 01, @07:36PM
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Is Shahriah Afshar related to the stunning Sarah Afshar? Sarah is rumored to be dating rookie QB Ben Roethlisberger.
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