Study Says Quantum Wavefunction Is a Real Physical Object 373
cekerr writes with this excerpt from an article in Nature
"The wavefunction is a real physical object after all, say researchers. ... the new paper, by a trio of physicists led by Matthew Pusey at Imperial College London, presents a theorem showing that if a quantum wavefunction were purely a statistical tool, then even quantum states that are unconnected across space and time would be able to communicate with each other. As that seems very unlikely to be true, the researchers conclude that the wavefunction must be physically real after all. David Wallace, a philosopher of physics at the University of Oxford, UK, says that the theorem is the most important result in the foundations of quantum mechanics that he has seen in his 15-year professional career. 'This strips away obscurity and shows you can't have an interpretation of a quantum state as probabilistic,' he says."
Proof by disbelieving .. (Score:5, Insightful)
This is what they have proven:
If a quantum wavefunction is purely a statistical tool, then quantum states that are unconnected across space and time are able to communicate with each other.
The rest is speculation.
IMO one observer's wavefunction is the other observer's statistical tool, where an observer is any ensemble of particles.
By the way, the wikipedia article on Bell's inquality stated something similar years ago.
Nothing unreal exists (Score:1, Insightful)
Everything is physically real. Stored Information is physically real. Concluding something is physically real says nothing useful about what it is or its properties.
To quote spock "Nothing unreal exists"
Re:Proof by disbelieving .. (Score:5, Insightful)
If a quantum wavefunction is purely a statistical tool, then quantum states that are unconnected across space and time are able to communicate with each other.
Actually, what they've proven is that either the wavefunction is a real object and not a statistical tool or quantum states that are unconnected across space and time are able to communicate with each other.
This is fairly similar to, though not the same as, Bell's Theorem.
The rest is speculation.
The paper is actually quite clear on their claims. The speculation was added by others, but is a reasonable interpretation.
What's definitely speculation is your comment, which seems to have no real basis in quantum mechanics:
IMO one observer's wavefunction is the other observer's statistical tool
Re:Nothing unreal exists (Score:4, Insightful)
Nothing unreal exists
That's an uninteresting tautology.
Everything is physically real.
This, on the other hand, is not true. Plenty of things have no physical reality: like abstract concepts. There is no physical quantity of "good" or "evil", for example. There's not even a physical quantity of "red" (not counting the unrelated color charge from QED). There are physical properties that make things red, but "redness" is not by itself physical.
One class of things that is not physically real is probability distributions. They describe information we possess about a real quantities, but the distribution itself is not real. They're common in statistical mechanics as well.
Re:Weird (Score:4, Insightful)
Sure you did, it's called Occam's Razor. Which is more likely: All the planets in the solar system travel around the sun in approximately elliptical orbits OR All the planets in the solar system orbit the Earth in a complex arrangement of circles within circles within circles? Now that being said, I'm not sure that you can arbitrarily say disconnected quantum states are likely than connected ones, but allowing them to communicate would seem to posit some communications medium that we have never seen evidence of, so if I had to choose I'd say they are unable to communicate.
And besides all that, as many people have already pointed out, the claims of 'proof' have been added by the media; the actual research just says it's one or the other making no judgement as to which.
Re:Nothing unreal exists (Score:1, Insightful)
This, on the other hand, is not true. Plenty of things have no physical reality: like abstract concepts.
Nope, the concept is physical real. Its a collection of organized molecules stored in various places in the universe which we interpret into thoughts. Those thoughts are the results of chemical reactions in the brain ... all very real things.
Just because it isn't a specific object you can grab without killing yourself doesn't make it any less real. You're trying to define it out of existence, which is a logical impossibility. It exists because you define it, Ergo Cognito Sum. There is a physical item backing your existence just like there are physical objects backing abstract concepts. Those physical objects just also happen to be part of your mind.
Is your consciousness not real?
Re:Weird (Score:2, Insightful)
I blame the trend in the 90's of feeling it was unfair to the stupid children to point out they're stupid.
Now an entire generation thinks their beliefs are facts because their dimwit parents and teachers never pointed out to them that they were idiots.
Re:Nothing unreal exists (Score:5, Insightful)
Bad example (Score:5, Insightful)
Copernican theory was picked up fairly quickly because it offered a simpler view of the cosmos. Astronomers bought into it largely because of its simplicity -- in effect, following Occam's Razor. It took until the early twentieth century for Einstein to say "you're all a bunch of doofuses: Ptolemaic theory is just as valid as Copernican, it all depends on your frame of reference." Thanks to relativity we now know beyond any shadow of a doubt that Ptolemaic epicycles are equally valid: they're just more complex. There is no privileged frame of reference. It is as true to say the Earth circles the Sun as it is to say the Sun circles the Earth -- it's just that the equations are neater in one frame of reference, not that they are correct. This bears repeating: according to special relativity, there are no privileged frames of reference.
Naively applying Occam's Razor to the question leads people to a false sense of certainty: they tend to think, "I've applied Occam's Razor, therefore I am likely choosing the better answer," without ever thinking, "did I formulate the question correctly in the first place?"
Don't get me wrong, I like Occam's Razor. But when people use Copernican-versus-Ptolemaic theories as an example of Occam's success, well... that tells me a quick lesson needs to be given on how Occam's Razor utterly fails in that case.
Re:Proof by disbelieving .. (Score:4, Insightful)
Re:Weird (Score:4, Insightful)
Then your physics degree is worthless.
One of the most basic principles of science, in fact I would say it's the single most important principle in science, is that nothing is ever completely proven. It's only probabilistically proven, meaning the chance of it being wrong is so small that you can basically rule out that possibility.
What is the concept of falsifiability, one of the key principles in the scientific method? You try everything you can to disprove your hypothesis. You get everyone else to try and disprove it. You hit it with everything you've got, and if it withstands the assault, then you can say it's proven. But it's only proven to be true under the conditions that you used to test it. In other words, no matter how hard you try, it still might not be true. It's only extremely unlikely not to be true.
Ironically, that's the greatest strength of science - that it's fallible. And it openly admits that fact. It rejoices when somebody tells it that it was wrong all along, because that means there's still more to discover. That's the driving force behind science. We test what we can, claim something is proven after the tests support it, but always leave open the possibility that we'll discover some new information that helps to refine or sometimes even replace the theory. The only "proof" of anything is the claim that it's a more likely explanation of your observations than any other possibility.
Granted, the claim that something is unlikely is not itself sufficient to disprove it, and perhaps that's what you meant, so maybe I'm being a little harsh. My point is simply that every "proof" is still just a claim. It just happens to be the claim most supported by the evidence.
Re:Alternative... (Score:3, Insightful)
Not quite; the paper hinges on having in existence a lambda that is a complete physical state that is the superset of the various properties defined by the wavefunction. That seems, at first, like a hidden-variable theory, which would come back to your statement. However, all they are saying is that the statistical interpretation allows for a generator of a pure state may yield a physical state that can "collapse" into the other state.
I am not very happy with at least the first argument (have not worked my way through the second) since the initial assumption breaks the preparation, as I see it, because having lamba be compatible with either of two unequal, pure, non-orthagonal states implies that the only part of lambda that can yield independent measurements is the set of properties not in the intersection of |phi_0> and |phi_1>. That would seem to imply that lambda cannot be generated by either a generator of pure state |phi_0> or |phi_1>, unless I am missing something important.
Re:Bad example (Score:1, Insightful)
Um. The earth is not an inertial frame of reference. The forces causing the earth to orbit the sun, and not vice versa can be observed directy.
Special Relativity does not state that all propositions are equally true. It simply elaborates the interesting consequences of the measured speed of light being the same in every frame of reference.
Except ... (Score:5, Insightful)
I could go back a couple of centuries and make the same flawed logical argument - "as it is unlikely that the earth moves, therefore it MUST be the center of the universe."
Re:Alternative... (Score:5, Insightful)
Because if the "wave function" is a real object, then there is no probabilistic nature to quantum shit - it just means we are currently unable to directly measure the "wave function" without "collapsing" it. If it's not probabilistic, all the fuzziness of quantum physics goes away. Schrodinger's cat is dead, Einstein was right when he said God doesn't play dice, entanglement is horse shit, everyone who works with string theory is a moron, etc.
Wrong. (And yes, I am a physicist working in quantum information)
The canonical formalism contains the "collapse" of the wave function on observation, and this collapse is probabilistic. And there are interpretations of quantum mechanics with real wave function and real collapse (e.g. the Ghirardi–Rimini–Weber theory). Now there also exist deterministic interpretations of quantum mechanics which also include the wave function as real object (such as Bohmian mechanics). In other words, the wave function being real is completely independent of the question whether the world is fundamentally deterministic or not.
By the way, the paper does not really prove that the wave function is real. What it proves is that if you assume that there is something like a real state of the quantum system at all (and assuming quantum mechanics is actually right) then that real state must include the full wave function. There are some physicists who claim that quantum systems don't have physical states at all (an idea known as Quantum Bayesianism). That assumption is not refuted by this paper.
And entanglement is a property of wave functions, therefore if wave functions are real, then obviously entanglement is real.
Re:Sensible (Score:2, Insightful)
The fact that you can do math with it is empirical proof that it exists. If it didn't, you couldn't do math with it.
Wait, what? Copenhagen is nonsense? (Score:5, Insightful)
The fact you called MWI "scientifically plausible" should be the first sign you don't have the first clue what you're going on about.
For MWI to be "scientifically plausible" it would have to make predictions which could be confirmed or falsified via experiment. That is, in essence, what science is: the subjecting of ideas to experimental test. (Go ask Zombie Feynman [xkcd.com] if you don't believe me.)
I've yet to hear any testable predictions MWI makes that would allow us to differentiate it from, say, Copenhagen. Maybe that's changed since I last dove into things (and if it has changed, I hope you'll tell me so), but I kind of doubt it.
David Deutsch is famous for saying that MWI is the only interpretation that gives any kind of sense to quantum computation. And, you know, I'm inclined to agree with him. That doesn't mean MWI is correct, though: it just means that the other interpretations do not satisfactorily explain those phenomena, not that MWI is the only possible interpretation that could give sense to quantum computation.
Also, given Copenhagen was first developed by Werner Heisenberg, it's kind of crazy to claim that Copenhagen is a "superstitious and completely nonsensical" interpretation. If I have to choose between exa on Slashdot being right when he says Copenhagen is superstitious and completely nonsensical, and Zombie Werner Heisenberg being right when he says that exa on Slashdot is misunderstanding Copenhagen, well... I'm going to side with Zombie Werner Heisenberg, you know?
Poor summary, poorly written article (Score:5, Insightful)
What a crappy summary and crappy article. The wavefunction is no more a real object than any other mathematical function. The statement: "f(x)=x^2 is a real object" has no valid meaning whatsoever. To even call it a theorem is ridiculous. Likewise goes for the wavefunction. It is a tool to model our "real" world. Some models are exact and precisely describe the "real" world. Other models only work under certain assumptions and/or reference frames.
If you actually read the research paper, the authors consider the question of whether a quantum state is a physical property attached to a system. Said another way, do quantum systems actually exist? Or are they purely theoretical? From the article:
"The statistical view of the quantum state is that it merely encodes an experimenter's information about the properties of a system. We will describe a particular measurement and show that the quantum predictions for this measurement are incompatible with this view."
The gist of it is that they have produced a result (didn't read the whole thing to actually figure out what their result was) which relied mainly on three assumptions:
Since their result is incompatible with the statistical view of quantum states, it must due to one of the assumptions above. They don't actually make the claim that quantum states are physical properties (like length, width, height, mass, etc. are). In fact, they conclude with:
"More radical approaches are careful to avoid associating quantum systems with any physical properties at all. The alternative is to seek physically well motivated reasons why the other two assumptions might fail."
Re:Bells theorem (Score:4, Insightful)
Wrong. Bell's theorem's implication is that there are no local hidden variable theories which can explain quantum mechanics. Non-local hidden variable theories are not excluded by Bell.
I'd even go one further -- it isn't clear what Bell's theorem implies as soon as you make quantum mechanics properly relativistic and time reversible within a closed physical universe, so that the measurement process it relies on no longer involves entropy in the form of an uncontrolled interaction with a classical measuring apparatus in an unknown microstate. In other words, Bell's theorem is completely meaningless as far as the nature of the actual state or nature of the Universe is concerned; it at best describes a theory of time-ordered, entropy based, projective measurements on open quantum subsystems.
As far as that is concerned, how could one NOT interpret the wavefunction as being "real" (given that a rather lot of it is imaginary if not quaternionic or a number in a generalized geometric division algebra of higher grade:-). It's no more real or less real than any model of a postulated external reality based on our sensory impressions and data, reinforced by reason-based statistical inference.
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(Yeah, yeah, I get it, they are really just trying to say that "time-ordered phenomena apparently exist so the wavefunction must be real", but why bother?. Did any physicist for the last sixty years or so ever doubt this? Should they have, any more than they doubt that reality itself is real and we aren't really all power units in The Matrix?)
Re:Oh man, University flashbacks (Score:5, Insightful)
The "interpretation" of Quantum mechanics has been going on for a long time and it has nothing to do with the result. Nothing changes. The math doesn't change. The predictions don't change. Nothing measurable changes. In fact its still what it always was, a way to predict the outcome of a experiment, often to very high levels of accuracy. Pushing meaning beyond that is philosophy. That is: untestable.