Slashdot Mirror
Study Says Quantum Wavefunction Is a Real Physical Object
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."
One of the stumbling blocks for learning this stuff at school was the people were hung up on the idea of "this-space", "that-space". It was a revelation to me that when they said "probability space" it was only a space in the mathematical sense (ie, something with N dimensions that could be graphed if N were not too large).
The way I saw it, people were prejudiced to believe that these were real spaces, the prejudice being that physics is strange at that level, thus there must be strange bizarre types of space. Nope. They were just things with N numerical characteristics.
Now you're telling me there really are strange spaces? That sucks.
"Abstract objects" or "mathematical objects" don't exist in general, so this suggestion is rather plausible. Of course, the reality of the wave function had been proposed before, but new arguments are sorely needed in philosophy of quantum mechanics.
--exa--
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.
Hey don't blame me, IANAB
Yes yes... Some amazing American innovation done at the ... Imperial college of... London?
They mean London, Arkansas, right?
I don't remember covering 'proof by claiming that something is unlikely' in my Physics degree.
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.
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.
An instance of considering an abstract concept -- which is what the collection of molecule is -- and the concept itself are different.
It's like people on Slashdot don't even know basic philosophy. I suppose that would explain why so many people thought The Matrix was interesting.
Its more like this mathematical construct we had to describe something we really didn't understand ... but let other mathematical constructs work out properly and achieve results that matched reality ... in fact appears to be the proper mathematical construct to define a portion of reality.
But thats what the summary says, not what the article says.
What the article says is more long the lines of:
Well, either this math is right or faster than light communications are possible. As far as we can tell, we see evidence that suggests faster than light communication is possible, so we conclude that we were probably right about this mathematical construct.
Considering that we have conflicting (and also unproven) reports of faster than light travel, we have two directly conflicting scientific theories on the table at the moment that can not possibly be right.
Or it could just mean that neutrinos are faster than light and the universal speed limit is actually neutrinos speed, not photon speed.
Truth be told, it all doesn't matter until we achieve the speed of bad news.
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Oh grow up. This kind of bullshit philosophy drives me nuts. Just because the idea is stored somewhere in a physical arrangement only makes that specific instance of the idea as pertains to a human being able to recall it real. It does not make the subject of the thought real, which is what we're talking about. Nobody is denying thoughts manifest in physical ways, but just because I can think about a unicorn doesn't make the unicorn itself physically real, just the thought of it is physically real. If you don't understand the difference, you think too highly of your own intelligence.
If I can just reach out with my words and touch a butthole, just one, it will all be worth it.
Pandering, poorly written and not very funny?
This is the voice of World Control. I bring you Peace.
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.
Sheldon Cooper is going to be pissed.....
http://motls.blogspot.com/2011/11/nature-hypes-anti-qm-crackpot-paper-by.html
"Whatever way you choose to read the text [of the paper by Pusey et al], it makes no sense whatsoever. How they suddenly jump to the conclusion that there is a problem with the probabilistic meaning of the wave function remains completely mysterious."
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.
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."
The funniest thing is that this paper is coming out in the midst of the discussion of faster-than-light neutrinos. According to the interpretation presented in the article blurb at top, FTL neutrinos should be forbidden. If they actually exist, however, then that means that the quantum wave function really is a stastical thing and not a physical thing.
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.
The Tao of math: The numbers you can count are not the real numbers.
In the Nature blurb, there's a bit of discussion at the end that quantum states might all be linked, entangled or not.
In most physics classes, you learn quantum mechanics by calculating the interactions between isolated states. This thought process is natural and useful for certain areas of physics, but you end up worrying about hidden variables and how particles which are essentially in different universes can possibly communicate. This view does not need the wave function to be real, it can just be a statistical tool.
An alternative way of thinking about things is the idea that there are no isolated states (and no measurement apparatus which can exist outside the quantum system). From that point of view, one wave function is sufficient to describe the entire universe, traced back to the big bang. You don't need to worry about spooky action, everything obeys causality just fine assuming the wave function is real. There are some cosmological issues still, and it's not clear such a unified state is possible in an infinite universe.
At least we're starting to all agree wave functions are real and not just a statistical tool.
"Concepts" cannot exist at all without some form of persistence. The persistence relies on physical objects (though I won't limit that to "chemical reactions" nor "in the brain" as per the parent post).
If a civilization develops the concept of boolean algebra, and then that civilization is completely destroyed and all record of the concept of boolean algebra is lost, "boolean algebra" ceases to exist. If another civilization arises and redevelops a concept that is in all respects similar, it is still not the same concept.
One could pretend to be an "outside observer", and compare the two concepts and call them the same concept, but then you have violated to conditions -- you have kept a record of what the concept from the destroyed civilization was, and that record exists in some physical form in order to get it from timespace A to timespace B.
Now it is tempting to say that since concepts like boolean algebra are developed methodically with a set of indisputable rules from axioms that they are "real" without being physical, but that presupposes that even stating the axioms does not rely on physical phenomena.
In other words, "mathematics" is really a verb when you get right down to it.
Someone had to do it.
I think it's great.
I think the wave function is a physically real object(*), and the randomness is not intrinsic or magically special but comes from thermodynamics and chaos, and, yes, Einstein was right: Copenhagen is a nonsensical load of bollocks.
More specifically that dice are not actually random in an ineffable sense, but their practical use has a sufficiently high Kolmogorov-Sinai entropy rate (roughly average amount of chaos generated per time) that they're random enough. In other words, quantum mechanics is regular physics, not mystical Copenhagen mumbo jumbo. Copenhagen works for computation, but that's because it's a very useful approximation for experimentally relevant circumstances, just like Fermi's "Golden Rules". Einstein was right, at least about the problem. His proposed solutions weren't, but the experimental evidence wasn't available until after he died and obviously he would have changed his mind given new results, because he was a physicist foremost and not a mystical philosopher.
Entanglement and uncertainty principle are not horse shit, because the central mystery of QM, that everything is operating in a Hilbert space still remains.
(*) To me, physically real means "acts as a source term in gravitation". This pretty clearly distinguishes "electrons/protons/photons" from "set of all sets of sets" crap and is as useful as any other description I know. Of course we don't have quantum gravity working yet but when we do it's pretty likely something like the wavefunction will be in there.
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 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?
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."
Bell's theorem's implication is that their are not "hidden variable" theories that can explain quantum mechanics.
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.
rgb
(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?)
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.