Quantum Physics Parts Ways With Reality 568
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.
What does it mean for us to observe something? (Score:3, Interesting)
Logic? (Score:3, Interesting)
"We have experimentally excluded a class of important non-local hidden-variable theories. In an attempt to model quantum correlations of entangled states, the theories under consideration assume realism, a source emitting classical mixtures of polarized particles (for which Malus' law is valid) and arbitrary non-local dependencies via the measurement devices. Besides their natural assumptions, the main appealing feature of these theories is that they allow us both to model perfect correlations of entangled states and to explain all existing Bell-type experiments. We believe that the experimental exclusion of this particular class indicates that any non-local extension of quantum theory has to be highly counterintuitive. For example, the concept of ensembles of particles carrying definite polarization could fail. Furthermore, one could consider the breakdown of other assumptions that are implicit in our reasoning leading to the inequality. These include Aristotelian logic, counterfactual definiteness, absence of actions into the past or a world that is not completely deterministic. We believe that our results lend strong support to the view that any future extension of quantum theory that is in agreement with experiments must abandon certain features of realistic descriptions."
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I may be a simple man but a breakdown in Aristotelian logic? What are they going to use to argue against logic? I would assume logic.
The Universe (Score:3, Interesting)
full, mangled text (Score:1, Interesting)
Simon Gröblacher1,2, Tomasz Paterek3,4, Rainer Kaltenbaek1, S caronaslav Brukner1,2, Marek Z dotukowski1,3, Markus Aspelmeyer1,2 & Anton Zeilinger1,2
1. Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria
2. Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria
3. Institute of Theoretical Physics and Astrophysics, University of Gdansk, ul. Wita Stwosza 57, PL-08-952 Gdansk, Poland
4. The Erwin Schrödinger International Institute for Mathematical Physics (ESI), Boltzmanngasse 9, A-1090 Vienna, Austria
Correspondence to: Markus Aspelmeyer1,2Anton Zeilinger1,2 Correspondence and requests for materials should be addressed to M.A. (Email: markus.aspelmeyer@quantum.at) or A.Z. (Email: zeilinger-office@quantum.at).
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Abstract
Most working scientists hold fast to the concept of 'realism'--a viewpoint according to which an external reality exists independent of observation. But quantum physics has shattered some of our cornerstone beliefs. According to Bell's theorem, any theory that is based on the joint assumption of realism and locality (meaning that local events cannot be affected by actions in space-like separated regions) is at variance with certain quantum predictions. Experiments with entangled pairs of particles have amply confirmed these quantum predictions, thus rendering local realistic theories untenable. Maintaining realism as a fundamental concept would therefore necessitate the introduction of 'spooky' actions that defy locality. Here we show by both theory and experiment that a broad and rather reasonable class of such non-local realistic theories is incompatible with experimentally observable quantum correlations. In the experiment, we measure previously untested correlations between two entangled photons, and show that these correlations violate an inequality proposed by Leggett for non-local realistic theories. 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.
Physical realism suggests that the results of observations are a consequence of properties carried by physical systems. It remains surprising that this tenet is very little challenged, as its significance goes far beyond science. Quantum physics, however, questions this concept in a very deep way. To maintain a realistic description of nature, non-local hidden-variable theories are being discussed as a possible completion of quantum theory. They offer to explain intrinsic quantum phenomena--above all, quantum entanglement1--by non-local influences. Up to now, however, it has not been possible to test such theories in experiments. We present an inequality, similar in spirit to the seminal one given by Clauser, Horne, Shimony and Holt2 on local hidden variables, that allows us to test an important class of non-local hidden-variable theories against quantum theory. The theories under test provide an explanation of all existing two-qubit Bell-type experiments. Our derivation is based on a recent incompatibility theorem by Leggett3, which we extend so as to make it applicable to real experimental situations and also to allow simultaneous tests of all local hidden-variable models. Finally, we perform an experiment that violates the new inequality and hence excludes for the first time a broad class of non-local hidden-variable theories.
Quantum theory gives only probabilistic predictions for individual events. Can one go beyond this? Einstein's view4, 5 was that quantum theory does not provide a complete description of physical reality: "While we have thus shown that the wavefunction does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists. W
Time to break out the ol' dictionary (Score:1, Interesting)
That the chair I'm sitting in can affect and be effected by, oh, the Voyager spacecraft in a shorter spacetime than c allows does not mean that either my chair or the spacecraft do not actually exist if they are not observed. It may mean that the concept of my "cone of effect" is a bad one, and that I am not solely affected by those things within X distance of me.
Quantum Mechanics is a terrible term in and of itself, and essentially every part of it is handicapped by having equally terrible names applied thereof. Words with actual meaning are used in a way entirely separate from their meaning, because scientists, by and large, could not be bothered to coin genuinely new terms. Science suffers for this, and the mind-numbingly slow pace of advancement on the cutting edge is only half the problem.
Re:First Post! (Score:1, Interesting)
If there is no reality R, how can we part from R and create unreality R^(-1) ? In order for unreality to exist, we must first have reality as an inverse state.
*BTW, I hope no one spent 30min trying to work out what the above two lines meant. Their meaning was lost when I looked away from the screen/keyboard while typing to attend to more important matters in the realm of "reality".
Bleh, no real new science here (Score:5, Interesting)
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.
Re:What does it mean for us to observe something? (Score:3, Interesting)
There seems to be a flaw in that.
It implies every thing is, in one way or another, being observed by something.
That would mean that all things are observed at all times.
And that would sort of do away with the premise of the article that things are not necessarily there unless observed.
Which might not be all that bad a deal --at least it would explain why everything stays the same when I come back to observe it again myself.
I suppose this means I'll have to give up on the possibility that one morning I'll wake up and only geeks will have girlfriends.... and that I'll be a super hero...
Bummer.
Re:bye-bye! (Score:3, Interesting)
Entanglment Applications Exist (Score:4, Interesting)
"quantum entanglement would be pretty cool if an applicable use was found for it.
Applications already exist [physicsweb.org], at least if you count the demonstration of instantaneous transfer of information regardless of distance. And this experiment is years old.
So yes, quantum entanglement is indeed pretty cool.
They're not saying the universe needs us to look. (Score:5, Interesting)
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.)
Re:bye-bye! (Score:3, Interesting)
The "features" (Score:2, Interesting)
"These include Aristotelian logic, counterfactual definiteness, absence of actions into the past, or a world that is not completely deterministic."
We've had many experiments that demonstrate concepts some people just can't handle. The "classic"
If QM didn't so accurately describe a large number of events, no one would care that it violates their preferred "reality". It's like with the "information loss" when matter/energy cross the event horizon into a black hole. The indeterminacy and apparent irreversibility are at odds with some peoples' concept of how the universe works (mathematically, QM-scale events should be symmetric with regard to time).
Personally, I'd suggest that clinging to QM-incompatible notions, regardless of how well they've served to date, is less likely to provide a resolution to the discrepancy than accepting QM results as a basis for determining a more-inclusive reality of which those notions are a special case.
"Observation" does not require consciousness. It could just be that one of the photons interacts with a polarization-sensitive field in space.
Re:bye-bye! (Score:4, Interesting)
QM is a theory of information (Score:2, Interesting)
This subject is much like Plato's World of Ideas. - When we're not looking at a thing, but we are> thinking about them, do they exist? In Plato's world; yes.
Re:What does it mean for us to observe something? (Score:5, Interesting)
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.
Here is a paper that may refute TFA. (Score:2, Interesting)
http://xxx.lanl.gov/ftp/quant-ph/papers/9906/9906
Since I can't read the parent paper outside of the abstract it is hard to say. But I think that these two papers disagree in their conclusions.
Re:bye-bye! (Score:5, Interesting)
I was using "theory" in the sense that F = G (m1m2) / r^2 is the theory of gravity, and this [wikimedia.org] is a major part of the theory of QM. And, apparently, Newton didn't offer a philosophical "interpretation" for gravity*, while for QM we have "infinite number of worlds with consistently inconsistent histories entangling while moving backwards in time, located everywhere at once and communicating instantly", or whatever your favorite is
I am not saying that that part isn't important - Newton's theory was superseded by one rooted in such a theoretical/philosophical concept ("curved spacetime"), after all. Just saying that these theoretical models only become useful when they start making testable predictions.
* Came across this great quote from him in Wikipedia: And general relativity takes a similar position, it describes how matter/energy curves spacetime, but makes no attempts to explain why that would happen.
To put it another way - I agree with what you said.
Well, it makes sense (Score:5, Interesting)
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.
Re:Well, it makes sense (Score:5, Interesting)
Big things seem to move in simple and obvious Newtonian physics. But as we look smaller and smaller, things seem to jump from place to place, go through each other, and behave randomly. This is precisely what happens in a simulation as you approach 0 in floating-point. You can get seemingly random effects by adding very very small numbers together. It is also similar to what happens if an object in a video games moves very quickly relative to the the frame rate. The bullet may pass through things, especially other things moving quickly.
Maybe, in a few generations, we will be able to break out of this universe, and see what is really out there.
Re:Bleh, no real new science here (Score:3, Interesting)
There is new science here. What they have shown is that any "reasonable" nonlocal theory cannot reproduce the results of experiment (which are correctly predicted by quantum mechanics.) This is building on the foundations that Bell laid, but is a significant new result.
What they do is assume that the down-conversion source produces pairs of photons that have real polarizations. They then put some limits on the effects non-local variables can have by imposing the quite reasonable and experimentally fulfilled condition that the results of measurement at one detector on a sub-ensemble of photons that all have the same real polarization must depend only on local variables. This is must be the case to reproduce Malus' law (the cosine dependence of transmission of a linearly polarized photons through a linearly polarized filter.)
They then show that the influence of nonlocal variables cannot be both such as TO NOT mess up Malus' law for a single detector, and at the same time TO influence measurements at both detectors in such a way as to reproduce the correlation results that are observed experimentally (and predicted by quantum mechanics.)
The experiment involves measuring linear polarization in one branch and elliptical polarization in the other, rather than just sticking to linear polarizations a la Bell et al. This provides them with sufficient degrees of freedom to draw a stronger conclusion than one can from Bell-inequality violations alone.
This is a very nice piece of work, and very much in the spirit of Bell's original work. Amongst other things it would appear to kill Bohm's theory because it will not be able to reproduce the predicted correlation results.
Re:Well, it makes sense (Score:3, Interesting)
Re:Crazy theories ahoy ! (Score:3, Interesting)
I come at the problem from a much more mathematical point of view, but ultimately I think your description is correct. For any given universe, there are rules that govern the behavior of everything in it. The thing is, for any set of rules there are an infinite number of universes that can exist within those rules. The important thing seems to be the rules that choose how any given universe will change. For me, consciousness exists as the ability for a system to model itself, e.g. something constructed within a system that mimics the entire system, rules and all. It doesn't have to be an exact model (which leads to Zeno like paradoxes), just a working model. In other words, if some part of a system is self similar to itself, that is the beginning of consciousness. When the self similar model can be manipulated by the same rules (encoded in the system) that govern the system itself to explore other possibilities for the configuration of the system, consciousness is complete. There is an extension to consciousness which is self action, which is partly separate from the model and has the ability to change the system itself based on interactions with the model. Self awareness occurs when the model includes a generalization of the self action itself, e.g. it knows that it is a model of the system with the ability to change the system. You can reverse the definition and say that the entire system is conscious because of its ability to change itself, but in precise terms the consciousness is limited to the model. If the model is destroyed, the system remains but consciousness is gone.
I'm also a modal realist in a strict mathematical sense. I believe that everything expressible with mathematics exists just as much as the universe, and probably the universe exists because of its expressibility in some form of mathematics. I also think that there are probably higher mathematical models than we can conceive of in this universe that also exist, but we don't have the resources to actually construct those models. Still, it's an interesting question whether set theory is sufficient to describe any possible model at any level, or if there needs to be something else bigger than set theory (and category theory) to describe something. My guess is that there is, but those are the kinds of things we won't be able to imagine in this universe.
I still think the Universe isn't a simulation, because some
Yes and no. Mostly no. (Score:3, Interesting)
Floating point errors tend to be more chaotic and unpredictable. QM is actually quite predictable and you can calculate useful stuff with it. E.g., it's not just that an electron in a potential well sometimes "tunnels through" (or rather, due to uncertainty principle constraints, it might have enough energy to jump or it might already be on the other side.) You can actually calculate how many will tunnel, and under which conditions, and build for example a Zenner diode. Mere floating point errors don't act that predictably, or not in the same way.
The thing about QM is... well, that QM doesn't actually have a problem. You can calculate stuff with any degree of accuracy, and, assuming you can actually design an experiment to simulate an measure it that accurately, chances are you'll get the expected results. The QM has been better validated than pretty much anything else.
Most of the conceptual problems you read about it are, basically, not problems of QM itself, but problems of the human imagination. The only problem is trying to imagine it, with a mind and in terms/concepts that were not made for that kind of problems. It's like trying to imagine a Beethoven symphony in terms of shapes and colours. That big a problem.
The human mind and your everyday experiences are based on macroscopic, Newtonian experiences. That is really why you find Newtonian mechanics simple. Your intuition helps you there. If I say "imagine a billiard ball hitting another" or "picture a ball rolling down a slope", you can conjure that mental image right away. You have tens of years of experience with that domain, and a brain which evolved to deal with that kind of problems.
When you move to Quantum Mechanics domain, your imagination and intuition fail you. (And me too, so don't take it as being snotty or anything.) You can imagine a particle, like a billiard ball. You can imagine a wave. (E.g., think: raindrops on a lake.) You _can't_ imagine something which acts fundamentally and thoroughly as _both_ at the same time. You can work abstractly with the concept, because you're undoubtedly a smart guy, but if you actually tried to really _imagine_ it, you'd probably just get a headache.
The "problem" is that people instinctively try to reduce it to one or the other, but each has its own problems:
- Thinking of, say, an electron as purely a particle, just like a small newtonian billiard ball, gets out of hand very fast. It does all these things, like mysteriously appearing on the other side of a potential barrier, which just aren't very newtonian.
- Thinking of it as purely wave, popular as it may be, is almost as big a mistake. Whenever you actually measure a state, you get a particle, not a wave front. E.g., if you put a phosphorescent coated screen (like that of a CRT) in the path of the electron, you get a single blip of light, not a fuzzy cloud over the whole screen. It only hits exactly one atom or mollecule of that phosphorescent coating, not all of them.
At any rate, that is the only problem: trying to imagine it all in a way that makes any sense to your macroscopic intuition. Even smart people who know QM well have a problem there. When you apply your intuition to it, it just doesn't make any sense. So all sorts of funny metaphors are invented to try to describe it... in words and concepts that just weren't made for that, and to a mind that wasn't supposed to imagine something like that.
Well, and then there are the people who _don't_ understand QM. Again, not meant snottily, it's a very hard and abstract domain. If it gives experts mind-cramps trying to wrap some intuitive sense around it, you can imagine how hard it confuses everyone else. So a thousand times more bad metaphors and mis-understandings get born that way.
Re:bye-bye! (Score:3, Interesting)
This is only true if you discard things we haven't figured out yet. Then again, the same can be said for literally any theory, correct or not. There was a point at which we had the phlogiston pretty well figured out too. We had Newtonian Dynamics nailed down well enough to predict the motions of everything from pinball to the celestial spheres. There was a point at which we could predict how much energy a fire would pull out of the Aether. Once upon a time, we knew the exact weight of the smallest possible particle, which we named the Electron. There was a time at which calculus contained all other mathematics (LISP programmers are nodding sadly right now.) There was a time at which the Principia Mathematica had not been torched by Godel and Erdos.
That quantum mechanics passes all our tests simply means the approximation is accurate enough that we don't know how to defeat it yet. All those other knowledges were well understood, well distributed, supported by the best science of the day, indicated by data, and passed every test we could throw at them. There was a time at which we knew how fast burning wood would disappear (though now we know it's just present in a different form as smoke and soot.) There was a time at which we knew how fast the heat in metal would die out (though now we know it's just being dissipated into the atmosphere or similar as thermal noise.) There was a time at which we knew the fourty three primary forces of the universe, though now we're down to gravity and the strong electroweak force.
One thing any trained scientist will tell you is that we don't actually know jack shit, and we never will. All we have are things we've eliminated, and a window of comprehension on the range of our current approximation.
Science was once certain that leeches helped with the bubonic plague. I'm not talking about the middle ages, I'm talking about 1860. They thought that one of the serious problems of the plague was that blood pressure increased catastrophically (the way the plague damages blood vessels looks like pressure bursting without microscopes; it's more like what happens to a tire if Scotty beams the radial belts out at 70 miles an hour. The system no longer handles normal usage.)
The thing is, leeches frequently have a parasitic bacteria that does happen to help a little bit with the plague. So, all our tests at the time - since we didn't know about things like germs until Robert Koch, despite van Leeuwenhoek's work - showed the leeches helping in cases we assumed were just not "too far gone already."
Fifty years later, we just used the bacteria. Now, we use a chemical those bacteria produce, in conjunction with another chemical that kills the plague disease, to thin the blood to reduce stress on the blood vessels.
Passing tests just means our tests aren't good enough.
Yeah, science always follows technology (Score:3, Interesting)
I mean, Euclidean geometry, Riemannian geometry, Ricci tensors, topology, Lorentz contraction, Maxwell's demon, algebraic set theory, noncommutative geometry, and Quantum Mechanics were all instances of science following technology.
It's an impossible thing to quantify without some sort of rigorous definition of technology, but I'd say technology follows science as much as science follows technology.
Re:bye-bye! (Score:3, Interesting)
One reason for not accepting this is the existence of the universe. If conservation of energy were not constrained to only work within a universe, then this would have required an unbelievable amount of energy.
FWIW, suppose that we take these results as proof that the universe is being run on a simulator. In that case multiple copies would result in greater consumption of ram, and slower execution, as observed from OUTSIDE of the universe, but from within the universe they would be unobservable. (This might also explain why the state of something is known only when it might be interacting with something eles.)
P.S.: I'm not asserting this theory. I merely wish to point out that it is consistent with observed evidence.
N.B.: AFAICT there are still five interpretations consistent with quantum mechanics.
1) Solipsism. (You can never rule that out.)
2) Superpredestinationism. (Every result was decided before the universe was set into motion.)
3) Many-Worlds
4) Copenhagen. (No understanding is possible. Only knowledge of statistics.)
5) The Participatory Universe. The future causes the past as well as the past causing the future.
Now these are all broad categories, so some of them come in multiple flavors, but they appear to all be consistent with what is known of quantum mechanics. (I have my doubts about Copenhagen, but it seems to still be popular with physicists, so it must be seen as reasonable, despite the models of understanding offered by the other approaches.)