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from the quantum-reality-is-just-classical-reality-in-really-tiny-bits? dept.
For nearly a century, "reality" has been a murky concept. The laws of quantum physics seem to suggest that particles spend much of their time in a ghostly state, lacking even basic properties such as a definite location and instead existing everywhere and nowhere at once. Only when a particle is measured does it suddenly materialize, appearing to pick its position as if by a roll of the dice. This idea that nature is inherently probabilistic -- that particles have no hard properties, only likelihoods, until they are observed -- is directly implied by the standard equations of quantum mechanics. But now a set of surprising experiments with fluids has revived old skepticism about that world-view. The bizarre results are fueling interest in an almost forgotten version of quantum mechanics, one that never gave up the idea of a single, concrete reality.
In a groundbreaking experiment, the Paris researchers used the droplet setup to demonstrate single- and double-slit interference. They discovered that when a droplet bounces toward a pair of openings in a damlike barrier, it passes through only one slit or the other, while the pilot wave passes through both. Repeated trials show that the overlapping wavefronts of the pilot wave steer the droplets to certain places and never to locations in between — an apparent replication of the interference pattern in the quantum double-slit experiment that Feynman described as "impossible ... to explain in any classical way." And just as measuring the trajectories of particles seems to "collapse" their simultaneous realities, disturbing the pilot wave in the bouncing-droplet experiment destroys the interference pattern.
Droplets can also seem to "tunnel" through barriers, orbit each other in stable "bound states," and exhibit properties analogous to quantum spin and electromagnetic attraction. When confined to circular areas called corrals, they form concentric rings analogous to the standing waves generated by electrons in quantum corrals. They even annihilate with subsurface bubbles, an effect reminiscent of the mutual destruction of matter and antimatter particles.
How about it Soylentils. Is there anyone here who groks Quantum Mechanics who would care to explain this in layman's terms? What shortcomings and/or benefits do you see with this theory?
(Score: 2) by HiThere on Tuesday July 01 2014, @07:59PM
I think Feynman would disagree with you. Particles are always switching modes, and personally I don't think they EVER stop, even for a measurement. My opinion is that the state vector doesn't collapse, but what is experienced is one one branch of the superposition, and that all the other branches are equally real...to those on them, including someone who's almost exactly me, but isn't quite the same me that is writing this. Different "branches" of the superposition (i.e., universe) have different levels of "probability" as indicated by "sum over histories" calculations. That those calculations are actually beyond us is irrelevant.
Now what an entity has to deal with is the branch of the superposition that it finds itself in, but that doesn't make the other branches unreal, merely not present. Parallel worlds is poetically accurate, not physically accurate. Splits happen at EACH measurement. AND branches can (improbably) merge, so that each present has multiple histories that are undecideable between. (I.e., just as one has all possible futures, one also has all possible pasts, with varying degrees of probability.)
OTOH, this is mere belief. There is no testable difference between this and the Copenhagen (Shut up and calculate) theory which one might call naive realism. And there are other models that are equally irrefutable, if not equally palatable. Everything is also compatible with "Super predestinationism", which is a solidly deterministic model that entails total determinism, with not choice at any point...from before the big bang. And to get silly, it's also compatible with Solipsism (nearly anything is). But the thing to notice is that while some of the models don't entail any predictions, others entail the same math that is used by the Copenhagen interpretation (which doesn't entail any particular math, being rather "these are the patterns we see when we go and look"). So the Copenhagen interpretation had to come before the EWG Multiworld interpretation, because it was built to match the math that the Copenhagen interpretation found. Nobody predicted that we would find what we found, so you can't use that as a guide to which is more accurate.
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(Score: 2) by kebes on Tuesday July 01 2014, @08:44PM
It is indeed usually said that the Copenhagen interpretation (CI) is experimentally and mathematically indistinguishable from other formulations. But I think it's a bit more subtle than that.
CI is indeed indistinguishable from other interpretations, if one is careful about how one describes it. However, I will note that many (sloppy) descriptions of it will claim that the wavefunction collapses at some size-scale. I.e. that QM is correct for small-scale systems but that wavefunction collapse always happens well before we get to macroscale systems. They are making a physical claim of some sort of non-deterministic physical process. In these formulations, one can experimentally falsify the claim by trying to generate ever-larger superpositions. And experiments done on ever-larger systems have yet to find a point at which a superposition cannot be maintained. So these collapse claims have been falsified (no one still seriously expects to find a size-scale at which quantum effects cannot operate.)
Of course there are CI descriptions that are more careful; and essentially say that the math of QM is all perfect, but just say that you shouldn't reify any of the theory's internal quantities. Which is fair enough.
But even this may not be the whole story. Experimentally, one can keep trying to generate larger and larger superpositions. One could even imagine a radically-challenging experiment wherein a human test subject is isolated and put into a superposition, such that the external experimenters can satisfy themselves that the person is, indeed, superposed. When the person is removed from the experiment (and becomes entangled with the rest of the universe), they will only remember a single sequence of events, but the experimenters will have experimental evidence that the subject was actually in a superposition. This would essentially falsify CI and support MWI. Or rather, the results can be explained in the framework of CI only in a very strained way; whereas they are precisely what MWI predicts. Similarly, you could in principle gather enough data to go looking for the influence of other branches (which, as you note, can still improbably interfere with our branch). Finding such correlations would support MWI and again be hard to explain in CI (which claims that the other branches don't exist).
Of course these proposed experiments are probably too difficult to carry out for real. But there may be a sense in which, at least in principle, some interpretations of QM are actually experimentally different.