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Quantum Physics Parts Ways With Reality
aeoneal sends us to PhysicsWeb for news guaranteed to induce headache in those wedded to the reality of, well, reality. Researchers from the University of Vienna have shown the violation of a stronger form of Bell's inequality known as Leggett's inequality. The result means that we must not only give up Einstein's hope of "no spooky action at a distance," we must also give up (some of) the idea that the world exists when we are not looking. From the article: "[Studies] have ruled out all hidden-variables theories based on joint assumptions of realism, meaning that reality exists when we are not observing it; and locality, meaning that separated events cannot influence one another instantaneously. But a violation of Bell's inequality does not tell specifically which assumption — realism, locality, or both — is discordant with quantum mechanics." From the Nature abstract: "Our result suggests that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned." Only subscribers to Nature, alas, can know what features those are, as PhysicsWeb doesn't tell us.
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you can find here http://arxiv.org/abs/0704.2529.
Humans don't have anything special to do with "observing" ("collapse of the wavefunction" or "state reduction"). A particle can be "observed" by a rock, or by any other "classical" macroscopic system with which it can entangle. Quantum decoherence in the consistent histories interpretation, IMHO, comes closest to explaining this process.
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We've known for a couple decades that EPR made local hidden variable theories extremely unlikely. The real competitors are non-local. Bohmian mechanics (de-Broglie pilot wave theory, really) is one such. Bohmian mechanics make all the same experimental predictions as normal Quantum Mechanics. Bohmians tend to think of Quantum Mechanics as a non-local theory that only appears local because you talk about probabilities instead of positions. The probabilities of Bohmian mechanics are actually just as local as Quantum Mechanics...
Not that Bohmian mechanics should be viewed as a correct theory. It's clearly an artificial construct. But it's a better theory than QM for the simple fact that it talks about particle positions instead of observers. One assumes, after all, that physics goes on even when physicists aren't there to observe it.
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As I read it they're not saying anything about the universe not existing when nobody's looking.
Quantum mechanics has a set of descriptions of matter/energy that "feel" incomplete.
To "classical physics" thinking the collapse of wave functions of entangled particles seems to require either some faster-than-light communication between the entangled particles (to tell the far one about how the near one was observed - violation of "locality") or some hidden variable (to carry information slower-than-light from the point in space-time where they became entangled to the point where each is observed - "realism" would include this hidden variable as part of the particles' state). Quantum mechanics doesn't describe either. It just describes a situation where this sort of thing just happens - in a way that you can't use it to carry information faster than light from one spacetime location to another.
Lots of work is being done to see if quantum mechanics can be "patched" into a more classical theory, in a way that preserves realism and locality by figuring out some way that a hidden variable can carry, from the entanglement to the observation at no more than lightspeed, the information necessary for a classical mechanism to produce the same result.
This work shows that some simple experiments have already eliminated a very broad class of such hidden variable theories - to the point that "realism" patches involving hidden variables carrying additional information with the particles looks pretty hopeless. This is another step toward the "quantum mechanics really is all there is to it" viewpoint.
(Of course I Am Not A Physicist so I could be reading it wrong.)
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Just how sure are we that the universe is comprehensible?
It's one of the axioms of science. It's not a question of being sure, it's a question of necessarily assuming it's true in order to proceed. There are basically three axioms you assume any time you're doing science, because there'd be absolutely no point to doing it if they aren't, and it appears science is useful, so we roll with the assumptions despite them being unproven (and in fact unprovable, even in principle).
First, we assume that nature is lawful. Things happen in accord with these laws and nothing happens except in accord with these laws. That doesn't necessarily mean the universe is deterministic or anything like that -- laws can be probabilistic, after all. In any case, since the point of science is to determine what the laws of the nature are, they better be there or the whole game is a fool's quest.
Second, we assume that the laws of nature are universal -- they're good any time, any place. If something behaves differently in one circumstance than another, this doesn't mean the laws change, it just means the laws are complex and take factors into account that make those two circumstances different with regards to them. We just need to understand the law completely to know why. This assumption needs to be true, or else there's absolutely no point in making observations or conducting experiments, since they would only tell you something about the laws in that place at that time. For observation and experiment to be useful, it must be the case that the laws apply in other places and times than the time and place of the observation.
And third, we assume that the laws of nature are comprehensible and discoverable. Again, the whole scientific endeavor is devoted to discovering these laws, and that's simply not possible if they aren't discoverable (and our being unable to comprehend them would preclude us from discovering them).
One could argue one doesn't have to believe these things are true to do science, but any time one does science, one is necessarily accepting them as axioms, assuming them to be true for the purposes of doing science, at least for the moment. I suppose you could ultimately view the scientific endeavor as a whole as a test of these three things. If it succeeds, it will have proven them true. If it ultimately fails in the end, perhaps they weren't. But of course you can never know that, it may be they were true, we just didn't manage to find all the answers, but in principle we could have. One can never be sure of success, either, so in the end, we'll never truly know.
But they've sure proven useful so far. If nothing else, one can make a mighty powerful pragmatic argument for thinking them true.
"Convictions are more dangerous enemies of truth than lies."
Well, it all makes sense, if you think of it. Whoever is running this MMO we call RL, can't possibly have the resources to simulate every single particle all the time. So until someone actually goes and observes the damn thing, there's no need to actually spawn/instantiate it.
Think of going farming for copper and tin ore in, say, the Gold Coast Quary in WoW. A particular ore spawn point might have been spawned as tin (most often), or as silver (rarely) or not at all. Would it already be spawned and in memory, if noone was there to see it? Or would it exist only as a probability until someone actually gets in range?
Or say you're hacking away at a copper ore vein with your trusty cold iron pickaxe, like a good dwarf. Sometimes you get just a piece of copper ore, sometimes you also get 1-2 pieces of stone, sometimes you get a Shadowgem, or a Tigerseye or Malachite. Were they already there before you started to hack at the ore vein? Or did they exist only as a probability until someone actually gets that loot window?
Of course, once you got a certain set of ore, stone and/or gems, closing the window and hacking at it again, won't change it. It stays the same set of, say, 1 ore, 2 stone, 1 gem until you actually loot them.
I can tell you, the best gnomish engineers and mages have worked hard for an answer to those questions, but everyone came up empty. We just can't figure out a way to see what's there without seeing what's there. Even warlocks sending their Eye Of Killrog into the mine didn't manage to fool the system. That and the eye got killed by the bandits in the mine. The best priests whined... err... prayed piously to the great gods of Blizzard, and got no answer. Etc.
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