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."
Oh man, University flashbacks (Score:5, Funny)
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.
Data vs Logic (Score:5, Interesting)
Re:Data vs Logic (Score:5, Interesting)
The latest experiments match the original observations. In the past day or so, they tweaked a number of parameters - such as the length of pulse - to see if more precise timing and more precise correlation would have any impact. The numbers didn't change. So, Scotty was wrong - we CAN break the laws of physics! (But the fine is 2795 Ningis if we're caught.)
Re:Data vs Logic (Score:5, Funny)
Since it is a quantum wave function, couldn't it be both physical and statistical at the same time?
Re: (Score:3)
Well, yes and no. It's not that easy.
Re: (Score:3)
The have a new test for the old interference patterns that can't be explained by ading the probability of the individual particles. They get the same result you'll find on any QM book, using a different test.
It is newsworth, but the news is wrong. The authors by their turn didn't help explain anything, the article does have almost the same claims people are repeating, not in a calm tone.
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.
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?)
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.
Sensible (Score:4, Interesting)
"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.
Re: (Score:3, Interesting)
"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.
The most shocking realization is this: Quantum Mechanics are ceasing to be Crazy, they're Real and Definite.
It's like a part of my childhood just died.
Re:Sensible (Score:4, Interesting)
There have been several scientifically plausible interpretations. One thinks of MWI for instance.
It's just that some rather big names have unwittingly advocated superstitious, and completely nonsensical interpretations, the most famous of which are Copenhagen interpretation, Von Neumann Interpretation, and Penrose's assorted BS.
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?
Re: (Score:2)
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.
His understanding of quantum computation is also astoundingly flawed.
Re: (Score:3)
Shor's algorithm is probably the best example.
In The Fabric of Reality, he says:
When Shor's algorithm has factorized a number, using 10500 or so times the computational resources that can be seen to be present, where was the number factorized? There are only about 1080 atoms in the visible universe, an utterly minuscule number compared with 10500. So if the visible universe were the extent of physical reality, physical reality would not even remotely contain the resources required to factorize such a large number. Who did factorize it, then? How, and where, was the computation performed?
His general view is that Shor's algorithm is performing the classical factorization computation but in parallel using quantum-mechanical superposition. (His argument from this is that the superposed states must map to alternative universes, but that's not really necessary to go in to.) This is a common but completely incorrect interpretation of Shor's algorithm. As far as I know, the only way to come to this incorrect understand
Re: (Score:3)
Correct, but we've also not seen any evidence of such things in physical reality. There's a lot of work going on in the axiomization of physics, but so far no one has been able to demonstrate the existence of things that are true but not testable by experiment. In the absence of that, I take the same attitude that I do towards string theory: it's an interesting idea, and I'll be very interested in reading about empirical results if/
Re: (Score:3)
Oh -- also, scientists don't use the phrase "null hypothesis" in the way statisticians do. Ask Richard Feynman, who seriously proposed a Journal of the Null Hypothesis which would publish good ideas that have been shown not to be the way the world works, in order to help keep other scientists from going down those same blind alleys.
If you want to say Feynman was falling into a fallacy, go right ahead. Me, I'm going to side with Feynman.
Re: (Score:3)
Coherence is not required for me to interact with the rest of the classical world, so why should it be required for me to interact with other universes?
It's required because otherwise your state vector gets entangled with the state vector of the rest of the universe, and then unitary time evolution requires that if you have a superposition alpha |psi_U> x |psi_O> + beta |psi_U'> x |psi_O'> [1] at time t = 0, and U(0,T) is the time evolution operator from time 0 to time T, then at time T the st
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: (Score:2)
Of course they exist. They have properties. Something non-existant can't be said to have any properties besides non-existance.
Re:Sensible (Score:5, Funny)
My salt and pepper shakers came as a set. They did not, however, come with salt and pepper in them. They were a - wait for it - Empty Set.
Hope I didn't break the maths too much.
Re: (Score:2)
Re:Sensible (Score:4, Funny)
Bertrand Russell walked into a cafe. He asked the waiter for a cup of coffee, with no cream or sugar. The waiter said "I'm sorry, but we're out of cream. Will you take it with no milk or sugar?"
Re: (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.
Re: (Score:3)
One can view complex addition as a shift in two dimensions; one can view multiplying by a complex number of modulus one as a rotation; and one can view multiplying by a real number not of modulus one as a compression or dilation.
Re: (Score:2)
Re: (Score:2)
> "Abstract objects" or "mathematical objects" don't exist in general,
Uh, if they don't exist, then how are you able to _refer_ to them then?
Ask any mathematician if infinity exists, and they will go "Of course, stupid". You are confusing existence with being dependent on the physical, when they are in fact meta-physical. i.e. Physical Existence is sufficient, but not a requirement.
Proof:
If time is physical, then show it to me.
If numbers are physical, then show it to me.
The fact that we can _separate_ m
Does this mean (Score:3)
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.
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:Proof by disbelieving .. (Score:5, Informative)
The big difference from Bell's theorem is that in Bell's theorem, the quantum states are entangled. Here they are not, and the idea that un-entangled states would be able to communicate with one another is a bit more problematic than the idea that entangled states would be able to communicate with one another.
Re:Proof by disbelieving .. (Score:4, Insightful)
Re: (Score:3)
In every experiment I've read about, the entanglement is known by how the particles are created. But here's the question I never see answered: is it possible, given two particles you know nothing about, to prove the particles are not entangled?
If you can't prove any given pair of particles are not entangled, then perhaps entanglement is the natural state, and particles known to not be entangled (
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Learn to logic
Okay Yoda.
Re: (Score:2)
No. If X then Y is equivalent to "X implies Y" in logic. Either X or Y adds the restriction that not X implies not Y. The common math phrase is "if and only if".
Re:Proof by disbelieving .. (Score:4, Interesting)
If quantum states that are unconnected across space and time are able to communicate with each other, then:
a) Single photons can interfere with themselves (has been done)
b) Interference patterns will work across time just as well as they can across space (has been done)
So unless I'm missing something, their claim that it is unlikely would appear flawed.
Weird (Score:5, Funny)
I don't remember covering 'proof by claiming that something is unlikely' in my Physics degree.
Re:Weird (Score:5, Funny)
Did they cover reading the paper instead of a media summary? Because it's a pretty important skill in science.
Re:Weird (Score:5, Informative)
This isn't science, this is slashdot. Facts are out the door here.
Re: (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: (Score:3)
"Now an entire generation thinks their beliefs are facts "
what do you mean now? it's always been that way, the 90s don't even enter in to it. The only difference now is they have ways to communicate their belief over a vast area.
And you should tell children they are stupid, but you should tailor education to what is challenging to the child.
Once you tell people are stupid, they start to internalize it and then thing they can't do anything.
Should they be told they are correct when they aren't? no. Should the
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.
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: (Score:2)
General principle of relativity [wikipedia.org]
Special relativity predicts that an observer in an inertial reference frame doesn't see objects they'd describe as moving faster than the speed of light. However, in the non-inertial reference frame of Earth, treating a spot on the Earth as a fixed point, the stars are observed to move in the sky, circling once about the Earth per day. Since the stars are light years away, this observation means that, in the non-inertial reference frame of the Earth, anybody who looks at the stars is seeing objects which appear, to them, to be moving faster than the speed of light.
Since non-inertial reference frames do not abide by the special principle of relativity, such situations are not self-contradictory.
My take is that it's better to pick the "most inertial" frame you have available. It is a heuristic like Occam's Razor but the upshot is the math is easier.
-l
Re: (Score:2)
Oh, sure. My own personal rule is "prefer the reference frame that makes the math easiest." However, my complaint was using Occam's Razor to decide which was more likely to be true: Ptolemy's or Copernicus's view of the heavens. This is a misuse of Occam: it overlooks the fairly deep truth that they are both equally true from within their given frames of reference.
Please, don't misunderstand me: I love making the math easier. :)
Re: (Score:2)
This. Occam's Razor is an experimental guide, not a standard of scientific proof. It's one of a number of maxims that gets abused by armchair scientists who think it says something it doesn't.
Likewise, this paper doesn't actually prove anything. It does appear to disprove one popular interpretation of quantum physics, by showing that it contradicts observed data. But by itself, that does not prove the other popular interpretation to be necessarily true.
Re: (Score:3)
Remember, theology isn't science, and Occam's Razor is used as a logical principle - it can't be disproved. ... Since there is never any direct experimental evidence, Occam is literally interpretable as a method to find the truth.
Again, it can't tell you whether anything is actually true or false, since the truth of Occam's Razor is simply assumed to begin with. As usual, this sort of theological "reasoning" is built on a house of cards. As a framework for encouraging a consensus on doctrine it served its purpose, but only in the context of writing internally-consistent fiction. That's appropriate, I suppose, given that the subject is theology.
Anyway, we're not talking about theology, or this weird variant of Occam's Razor, even if
Re: (Score:2)
What? It's not even close to true that Einstein showed Ptolemeic theory to be equivalent to Copernican theory. Ptolemeic theory postulated the existence of spheres of revolution, and epicycles on those spheres, and more refined versions had epicycles on the epicycles.
It's ok for you to be confused about physics. Many good people are. It's not ok for something this scientifically absurd to get modded +5 Insightful on a blog of nerds.
Re: (Score:2)
The AC has already answered this for me, so I'll just say it: yes, that.
Ptolemy's original vision was accurate for the measurements of the day. As observations got better, the model was patched -- as you say, with epicycles within epicycles. If we were to continue to patch the Ptolemaic version (which shouldn't be surprising, given how many patches we've made to the Copernican version), we would have an Earth-centric model of the universe with the heavens moving in strange, complex patterns around us. Th
Re: (Score:2)
That's also a bad example, nothing with Einstein was necessary. You can derive the equations of motion in the different frames perfectly well with Newton's mechanics (Einsteinian corrections are tiny), and yes the description really is simpler in some frames than others.
It was really Kepler's refinements which astronomers bought into, because of its experimental predictability; and then Newton explained Kepler's results from first principles, unifying gravitation on the ground and in the sky, which was the
Re: (Score:3)
This is quite untrue. By a 'privileged frame of reference', physicists have always meant ones in which the laws are particularly simple. There are, in special relativity, a privileged set of frames called internal reference frames. These are the same priviliged reference frames as existed under Newton's Laws. What Einstein did is hypothesize (to explain the negative result of the Michelson-Mo
Re: (Score:3, Informative)
The sun isn't an inertial frame of reference either. Both the sun and the earth orbit something called the barycenter, which is the center of mass of the sun-earth system. This just happens to be so near the center of the sun (because the sun is so massive) that for most intents and purposes, the earth can be said to orbit the sun.
This discussion, however, is not one of those intents and purposes.
Re: (Score:3)
A frame of reference is a coordinate system, nothing more. It's not a point of view or some state of mind that makes something true or false. Both the geocentric and heliocentric models can (and must) be compared o
Re: (Score:2)
Sure you did, it's called Occam's Razor.
Occam's Razor doesn't say anything about correctness.
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?
If they give the exact same predictions, both matching observations with the same accuracy and precision, then you take the easier to calculate one. And that is what Occam's Razor says, actually: that it makes no sense to use anything more complex than you have to. As for which one is "correct", if both give the same position to at all points to all the planets, that means they are equivalent.
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.
Yep.
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.
physical phenomenon (Score:2)
Don't you... (Score:2)
Why is it that reading this feels like I'm (Score:2)
watching The Big Bang Theory?
Re:Why is it that reading this feels like I'm (Score:5, Funny)
Pandering, poorly written and not very funny?
Prince de Broglie... (Score:3, Interesting)
Yawn. Did these guys ever read Prince de Broglie?
http://galileo.phys.virginia.edu/classes/252/Bohr_to_Waves/Bohr_to_Waves.html [virginia.edu]
http://en.wikipedia.org/wiki/Louis_de_Broglie [wikipedia.org]
A particle is a wave is a particle-wave; all we can say about the universe, is what we can say about the universe; there's no such thing as a "real physical object."
Re: (Score:2)
"The Duke" is already taken. And yeah, I figured the "real object" stuff came from the mind of the journalist, not the mind of a physicist :).
Would bounce as reviewer (Score:3)
I would bounce this paper as a reviewer. It appears to be a recasting of Bell's Theorem, but it doesn't reference ANY of that work.
Dumb question (Score:3)
Re: (Score:2)
What's the difference? What is the difference between something being a "mathematical description of reality" and being real? I mean you can go back and forth between if numbers are real, etc. Have they discovered something "more real" than they previously thought?
Math is the study of patterns.
Physics is the study of reality.
We use math to describe physics. Our current quantum math tells us what will happen. Our best quantum math is currently probabilistic. All our finest measurements can only give us a guess as to what will happen. The math describes what we see.
If the wave function is a result of a real, physical thing, we can potential learn more about the real, physical thing, and perhaps measure that, and get take that into account in our math, thus removing
Re:Dumb question (Score:5, Informative)
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.
Re: (Score:2)
It's a very good question.
I'm not a physicist, and I couldn't understand most of the paper, but what it seems to suggest is that a quantum state must be somehow represented or stored in a physical object. So the quantum state is not simply a statistical description of how particles interact, but is something 'real' that interacts with particles.
I would guess this physical object would take the form of a particle and also take the form of a wave, i.e. a wave-particle or whatever you call it, like many other
Multiple universes (universii?) (Score:2)
So does this support or refute the contention that reality is made up of a very very large number of universes constantly being created at each quantum step? Isn't that what the Copenhagen interpretation implied?
Re: (Score:2)
Probably neither, and that is a competing interpretation to the Copenhagen one.
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If the title of the Slashdot story were factually right, one could say that it in some sense support it. But no more than it also supports the notion that there are physical particles guided by the wave function in a single, non-branching universe. Because both interpretations assume that the wave function is physically real (as do some other do, like t
heh. quantum news. (Score:2)
Gotta love quantum news posts: meaningless and meaningful at the same time, like a newspaper written by Schroedinger's Cat.
Lumo weighs in... (Score:4, Informative)
http://motls.blogspot.com/2011/11/nature-hypes-anti-qm-crackpot-paper-by.html [blogspot.com]
"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."
Re: (Score:3)
Come on! Get a life. (Score:2)
Help me out here (Score:2)
the new debate (Score:5, Interesting)
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.
Its real, and .... (Score:2)
Stand by to see which theory Schrodinger's cat buries in his litter box.
Nothing to see here (Score:3)
I saw the paper when it originally appeared on the arXiv. They claim to randomly prepare a pure state. This is a contradiction in itself, as von Neumann and others have already shown decades ago that random ensembles of states (or local parts of a globally pure state) have to be described by mixed states. If one uses the proper mathematical concepts, their results vanish immediately.
Well, no (Score:2)
All they proved is that the simple statistical model is inadequate to describe why spooky-action-at-a-distance is not more commonplace.
Define Exist? (Score:2)
I'm sorry have I missed something, what does the term exists mean in this context?
Don't all ideas and mathematical constructs , including dreams exist? If they didn't we would not have words to describe them, because no one would ever have experienced them.
Is there some definition for the word exists that doesn't require recourse to metaphysics for it's definition?
I mean you might say occupies objectively measurable space time , but isn't that a pre-requisite for experimentally derived data?
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."
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It's not ridiculous at all, it's just counterintuitive. But then, intuition about such things is difficult at best.
Re:Alternative... (Score:4, Interesting)
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.
Re:Alternative... (Score:5, Funny)
Sheldon Cooper is going to be pissed.....
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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
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To make a simple analogy: Say you have two machines named "psi" and "phi" producing badges with numbers from 1 to 10 on it. Now it happens that the "psi" machine only produces even numbers, while the "phi" one only produces multiples of three. Other than that, the number produced by each of the machines is completely random. Now if you know you have a badge from machine "psi", but can't see the number, you still know that it might be a 2, a 4, a 6, an 8 or a 10, but you don't know it. So if you know the bad
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.
This is great for QM and physics. (Score:4, Interesting)
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.
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Because then wave-particle duality are really just the same thing? I don't know much about this subject, but it seems that we have to rethink light rays... ?
We can measure light as both a wave and a particle. But they are both physical? So is the particle a dot which waves? Or springs back to a dot and out again to a wave?
Who knows...
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"We can measure light as both a wave and a particle. But they are both physical? So is the particle a dot which waves? Or springs back to a dot and out again to a wave?"
The problem is more complicated than that, but it has been solved completely satisfactorily now with the proper application of quantum mechanics to electromagnetic fields, known as quantum optics, and verified experimentally.
Very toughly, light is a quantum mechanical superposition of the electromagnetic modes. A 'wave function of functions'
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The alternative was to treat the wave function as a purely mathematical object, and to interpret it purely in that way.
The difficulty here is what happens when you measure the position/momentum of an object? Does the wave function "collapse" to a point? What happens after you measure? Does it become a wave function again? What?
If the quantum spectral representation or orbitals something real, or is it just a mathematical convention analogous to Fourier series, or decimal digits? Should we see an electron as
Re:Bring back US jobs! (Score:5, Funny)
Yes yes... Some amazing American innovation done at the ... Imperial college of... London?
They mean London, Arkansas, right?
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Ladies and gentlemen please look to the to the AC above. Observe the unrelated statements, the illogical statements, and the excessive long list of names being laid out for no particular reason, in a very non-slashdotesque manner.
Gentlemen, and ladies, we have ourselves an employee of the misinformation industry.
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:Nothing unreal exists (Score:4, Interesting)
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.
Re:Nothing unreal exists (Score:4, Interesting)
"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.
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The persistence relies on physical objects
You are confusing the concept with the implementation. There's the abstract concept of a song. That abstract concept could be implemented as a videoclip [youtube.com], as a set of guitar chords [ultimate-guitar.com], or in many other ways [romancortes.com]. But in the end it's the same concept. Different physical implementations, same abstract concept.
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Those are things that make it entertaining, not interesting. Although I probably should have clarified that people seemed to think the ideas in The Matrix were interesting, when in fact they were simple, rehashed philosophy.
Re:Nothing unreal exists (Score:5, Insightful)
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I think you fail to understand what the term "abstract" means. My mind's conception of a circle may have a physical manifestation in my brain, but my mind's conception of that circle is not the abstract circle.
Before you start quoting Descartes, perhaps you need to revisit your Plato [arpast.org].
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So, if I throw wavefunctions equations at friends is that assult?
No. They'll just give you a funny look and ask what kind of drugs you are on.
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I always suspected he would end up working under Pusey.