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**quantum-reality-is-just-classical-reality-in-really-tiny-bits?**dept.For nearly a century, "reality" has been a murky concept. The laws of quantum physics seem to suggest that particles spend much of their time in a ghostly state, lacking even basic properties such as a definite location and instead existing everywhere and nowhere at once. Only when a particle is measured does it suddenly materialize, appearing to pick its position as if by a roll of the dice. This idea that nature is inherently probabilistic -- that particles have no hard properties, only likelihoods, until they are observed -- is directly implied by the standard equations of quantum mechanics. But now a set of surprising experiments with fluids has revived old skepticism about that world-view. The bizarre results are fueling interest in an almost forgotten version of quantum mechanics, one that never gave up the idea of a single, concrete reality.

In a groundbreaking experiment, the Paris researchers used the droplet setup to demonstrate single- and double-slit interference. They discovered that when a droplet bounces toward a pair of openings in a damlike barrier, it passes through only one slit or the other, while the pilot wave passes through both. Repeated trials show that the overlapping wavefronts of the pilot wave steer the droplets to certain places and never to locations in between â€” an apparent replication of the interference pattern in the quantum double-slit experiment that Feynman described as "impossible ... to explain in any classical way." And just as measuring the trajectories of particles seems to "collapse" their simultaneous realities, disturbing the pilot wave in the bouncing-droplet experiment destroys the interference pattern.

Droplets can also seem to "tunnel" through barriers, orbit each other in stable "bound states," and exhibit properties analogous to quantum spin and electromagnetic attraction. When confined to circular areas called corrals, they form concentric rings analogous to the standing waves generated by electrons in quantum corrals. They even annihilate with subsurface bubbles, an effect reminiscent of the mutual destruction of matter and antimatter particles.

How about it Soylentils. Is there anyone here who groks Quantum Mechanics who would care to explain this in layman's terms? What shortcomings and/or benefits do you see with this theory?

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## (Score: 4, Interesting) by Nerdfest on Tuesday July 01 2014, @01:33PM

If true it would once again push things back towards Einstein's "God does not play dice with the universe" statement, wouldn't it?

## (Score: 3, Interesting) by pe1rxq on Tuesday July 01 2014, @01:59PM

Yes and no.

If I understand the article correctly everything would be predictable, but there are to many unknowns and some of them are beyond our reach to measure.

So it would look like someone is rolling dice, but in reality the game is rigged and we are just not capable of measuring how they are loaded...

Parent## (Score: 0) by Anonymous Coward on Tuesday July 01 2014, @02:07PM

Wouldn't that be the case even if reality was probabilistic? How can you differentiate between determinism and a chain wave collapse reaction?

Parent## (Score: 2) by Geotti on Tuesday July 01 2014, @09:51PM

With one it's

possibleto know the rules, with the other it's ultimately random (tm).Parent## (Score: 4, Funny) by q.kontinuum on Tuesday July 01 2014, @03:44PM

Until someone looks at the reply more closely, than it will collapse to Yes or no.

SCNR

Registered IRC nick on chat.soylentnews.org: qkontinuum

Parent## (Score: 2) by Dunbal on Tuesday July 01 2014, @07:00PM

"If I understand the article correctly everything would be predictable"

That's mere black and white thinking and not necessarily true. In an infinitely sized universe with infinite variables, you'll never know them all and be able to fully predict absolutely everything. As it stands though science is pretty darned good at predicting most things, so it fits.

Parent## (Score: 2) by maxwell demon on Tuesday July 01 2014, @08:30PM

No, it would still be someone rolling dice. It's just that they would be pure classical dice: Unpredictable because you cannot know the parameters to infinite precision.

The Tao of math: The numbers you can count are not the real numbers.

Parent## (Score: 2) by romanr on Tuesday July 01 2014, @02:05PM

I can't find it, but the bouncing droplet analogy isn't new. There has been an article about this few years ago on /.. There is even an article on wiki [wikipedia.org] that describes analogies between quantum behaviour and bouncing droplet. Is this really so groundbreaking? Am I perhaps missing something?

## (Score: 4, Interesting) by Blackmoore on Tuesday July 01 2014, @02:27PM

well, the article points out this is old theorem, apparently "proven" enough that Einstein himself endorsed the idea by the 1950's, but it apparently has no traction do to Bohr's Quantum model that won the argument back in 1930's. it's a sad story of science actually having a working model - but the universities and most scientists either dont know about the theorem - or cling tightly to the bohr model.

Fortunately there is a 'new' group of researchers who've not only dug out this model but have working experiments to prove it - even if you can't really explain why it works.

Parent## (Score: 3, Funny) by VLM on Tuesday July 01 2014, @05:21PM

You make it sound like low carb / paleo weight loss dieting.

Parent## (Score: 3, Interesting) by MozeeToby on Tuesday July 01 2014, @05:26PM

The article makes out like this theory has absolutely no problems with it, which is not the case. Even if it could replicate every prediction of the Copenhagen interpretation (which it can't, though with enough work on the math it probably could) it would still be

non-local; that alone makes it a non starter for the vast majority of researchers. Yes, you can make the universe work without locality but you'd better have a much better reason than "well the math looks prettier".Also, they haven't "proven" anything with the recent experiments, they've shown that the theory is plausible in that it can generate results substantially similar to the probabilistic predictions of quantum mechanics by using classical interactions. That's very interesting, but it doesn't imply that the probabilities are fueled by an analogous set of interactions.

Parent## (Score: 2) by sjames on Thursday July 03 2014, @12:11AM

The latest round of experiments greatly expands on the number of verified similarities. For example, showing the fluid drop neatly behaving like an electron around a nucleus, complete with following orbitals and having quantized energy states.

Parent## (Score: 2) by c0lo on Tuesday July 01 2014, @02:32PM

If so, what a relief for the common-sense!

https://www.youtube.com/watch?v=aoFiw2jMy-0

## (Score: 2) by Oligonicella on Tuesday July 01 2014, @02:57PM

Please let us hope this sense propagates into the realm of cosmology as well.

Parent## (Score: 3, Informative) by romanr on Tuesday July 01 2014, @03:14PM

I have to react to your subject as this is very common misconception. Quantum mechanic as we know it ATM doesn't allow FtL signals (information transmission). Any FtL signals would mean time travel of information. (I'm not saying that information time travel is theoretically impossible, see: Novikov self-consistency principle [wikipedia.org]

Parent## (Score: 4, Informative) by MozeeToby on Tuesday July 01 2014, @04:53PM

FTL is already and quite thoroughly ruled out by the standard quantum explanations. Actually, the De Broglieâ€“Bohm theory (which is what the article is talking about) is explicitly

non-local, meaning it would at least in principle open up the possibility of FTL transmissions. As for quantum computing... just because the effects are deterministic wouldn't necessarily mean quantum computing is impossible, just that the explanation for it is different. The computations would be done in the nearly infinitely complex, chaotic interference patterns that all the qbits would be generating together.That said, the non-local nature of the theory (which the article conveniently neglects to mention) basically rules it out IMO. Everything we know about the universe indicates that locality is a central feature, throwing out locality just because you like the math better this way (in current form it makes no new predictions) would seem to me to be a bit foolish. Not that it shouldn't be researched necessarily, just that it gets lumped into a long list of "hypothetical" physics which break causality (worm holes, warp drives, negative mass, etc) and are therefore highly suspect

Parent## (Score: 2) by HiThere on Tuesday July 01 2014, @07:41PM

Well, non-locality is one of the possible solutions to the interpretation of Bell's Theorum. I, personally, prefer the WEG multi-world model, but I don't think the math changes. IIUC both are models that are compatible with everything in quantum theory (along with a few other models). There's no know objective test between the models, and this isn't one either, though it does make non-locality more plausible.

HOWEVER, whatever non-locality implies cannot rule out known phenomena, like entanglement at a distance. And it probably won't rule out quantum computing, as I believe that's predicted by the math, though the interpretation of how it happens may be different.

FWIW, I don't believe that quantum math rules out FTL, but, OTOH, I don't think it allows it either, unless you can stabilize a wormhole...and even then the distance through the wormhole may well be longer than the distance in ordinary space...but if you could send one end of the wormhole on a relativistic trip WRT the other end, you might get two way crosstime communication eventually. That's a sort of FTL. OTOH, the current knowledge seems to say that wormholes are too fragile to hold together under that kind of treatment, even with external bracing (see Casimir effect, negative energy, etc.).

Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.

Parent## (Score: 5, Informative) by kebes on Tuesday July 01 2014, @02:52PM

This isn't the version of quantum mechanics (QM) described in textbooks, or as used by actual physicists. This is a strawman view that is popular in science journalism, but it has little to do with actual quantum mechanics. (It is popular perhaps because it makes QM sound strange and thus interesting; but by purposefully making it sound weird, one makes it needlessly confusing.) I will try to describe the view that is now predominantly held by physicists, and actually embodied in the equations. (I'm a physicist, though not a quantum theorist by any means. On the other hand I happen to be preparing lecture notes for an intro-to-quantum class, so this is very much on my mind.)

Particles are not in "ghostly states". They do not lack basic properties. Every particle is described by a wavefunction, which fully characterizes the particle (indeed characterizes everything that can be meaningfully known about the particle). You can imagine this 'wavefunction' as describing a wave packet [wikipedia.org]; i.e. every particle is a somewhat localized wavelike perturbation. (I wouldn't say it lacks a definite location: it has a spatial extent described quantitatively by the wavefunction. Formally the wavefunction is defined over all-space, but that's not the same as saying it is "everywhere at once"; it's spatial distribution is completely and meaningfully described by the spread of the wave-packet.)

These wavefunctions evolve (and interact with one another) in a precise and deterministic way (given by the Schrodinger equation [wikipedia.org]). There is nothing random.

This is so wrong. The particle always exists. 'Measurement' is just a particular case of 'interaction'. In QM, particles are generally in 'superpositions [wikipedia.org]', which means the wavefunction is actually the coherent-summation of different sub-states (this is not just a mixture; the sub-states can 'interfere'). So one can have, e.g., a superposition of the wave packet being in two different spatial locations. (But you can also just think of this as a wavefunction with two maxima at two different locations.) When a particle interacts with another particle, the two wavefunctions become entangled [wikipedia.org]; that is, they form a combined system with interdependencies and more complex interference effects. When a particle becomes entangled with a very large number of other particles (e.g. the innumerable particles in a measurement apparatus, or even just all the atoms in the air bumping into it), then the combined system evolves in a complicated way. When you go through the math, it turns out that it evolves into a so-called 'mixed state', which means that the superposition has collapsed into what looks like a well-defined state (e.g. wave-packet is only in a single location). This is called decoherence [wikipedia.org].

This process looks random to a local observer (whether that 'observer' is a human, a measurement device, or just the surrounding environment), but the inherent process is actually deterministic. (There are subtleties I'm skipping over. In particular, why do we only observe one of the states in the mixed-state? The answer depends on how one interprets the mathematics; e.g. MWI [wikipedia.org].)

Quantum mechanics describes a deterministic evolution of well-defined entities. The modern interpretation of this mathematics is that reality is concrete, and well-defined. (Although somewhat different from human intuition; but that's true of many fundamental scientific truths.)

This article, like many pop-sci descriptions of QM, is still stuck in 1930's thinking. It ignores the progress of the last few decades. In particular, decoherence has gone a long way to explaining precisely how a seemingly classical reality emerges out of a fundamentally quantum microscopic physics. The answer (mentioned above) is startlingly simple: just take the laws of QM seriously, and apply them to realistic macroscopic systems (which have an absurdly large number of degrees of freedom). Once you do this, you will predict decoherence: the system becomes entangled with the environment, the delicate superposition is destroyed, and you end up with classical-like states. No magic required.

## (Score: 2, Interesting) by romanr on Tuesday July 01 2014, @03:09PM

Are you sure about this? I don't think there is general agreement about this. AFAIK there are people who say, that light is a wave, that sometimes behaves like a particles, others say that light is stream of particles, that sometimes behave like a wave. I think that the simplified view of TFS is more or less accurate. As I understand it, a particle is described by a wave function and when you measure it, you collapse it and force the particle to be in some point in space. It doesn't mean that the particle is in some definite point when it is not measured.

Parent## (Score: 5, Informative) by kebes on Tuesday July 01 2014, @03:34PM

There is indeed disagreement [preposterousuniverse.com] about fundamental interpretational issues even among quantum experts. But, importantly, no one is disagreeing about the mathematics or the predictions, there are only disagreements about what words to use to describe them, and how to interpret the results. (Of course there are also people looking for experimental deviations from QM, but that's another issue.) Yes, there are some physicists still using older phraseology; though even they typically wouldn't say things like "ghostly state" or "suddenly materialize". They would instead restrict themselves to saying things like "If you do experiment X you will get result Y. Whether or not the intermediate function psi 'really exists' is not a meaningful question."

At a minimum, I am making the point that there are clear-cut interpretations of modern QM that don't invoke silly notions like those espoused in the article. Also that modern QM mathematics (which includes decoherence) is deterministic.

Wave-particle duality is another historical misconception, rooted in classical thinking. As I noted above, it's more meaningful to say that real quantum entities are wave-packets. The 'ideal wave' (infinite/perfect sine-wave) and the 'ideal particle' (delta function at one specific location) are limiting cases that can be useful conceptually, but never actually exist in the real universe. It's always a wave-packet. Never an ideal wave. Never a pointlike particle.

One objection I have is that the article uses confusing language needlessly. Is reader comprehension enhanced by using words like "ghostly"? Even if you want to provide a probabilistic interpretation of QM, you can do so without invoking confusing metaphors.

However I also think the article is factually wrong. Saying that particles "[lack] even basic properties such as a definite location" is incorrect. As I said, the properties of the particle can all be meaningfully enumerated. Besides, why are "definite locations" a "basic property" of a sensible reality? Does it really make sense to have zero-volume entities localized to arbitrary precision? Just because classical physical theories assumed such a thing? Regardless of what your intuition tells you, when one measures Nature, one finds that it obeys QM. The properties enumerated by QM are the actual "basic properties" that reality consists of. (With the usual caveats that QM may one day be superseded by a better theory.)

P.S.: I know I'm being a bit confrontational about this. But bad pop-sci descriptions of QM, which ignore the last few decades of progress, are one of my pet-peeves!

Parent## (Score: 2) by Theophrastus on Tuesday July 01 2014, @03:44PM

With respects, (for someone demonstrating a profound passion about science reporting), i'd say quantum mechanics, even without a strong dose of then Copenhagen interpretation, does require the location of a particle to be indefinite. That is a the clear understanding that one gains by accepting the Heisenberg uncertainty principle. Or are you hereby declaring your rejection of the uncertainty principle?

Parent## (Score: 2) by kebes on Tuesday July 01 2014, @03:49PM

Sorry for being unclear.

Parent## (Score: 2) by Theophrastus on Tuesday July 01 2014, @03:59PM

So you're suggesting that

locationshould not be considered a 'basic property of reality'..? Do you have a substitute set of these properties? Because if you don't then i'd say your interpretation is rather classically Copenhagen. "notthat there's anything wrong with that" -- but you did seem to be rejecting the deep probabilistic nature presented there.Parent## (Score: 4, Informative) by kebes on Tuesday July 01 2014, @04:37PM

definitelocation", not location. The insinuation of the article is that the definite locations of classical physics (particles are zero-volume objects with positions given by real numbers with arbitrarily-high precision) is more real and more valid than the distributed locations of the wavefunctions that appear in QM (which it calls "ghostly" or whatever).I'm saying that empirically, when we study reality, we observe that it matches QM and not classical physics. How one interprets that is a matter of philosophical preference, but usually in science we accept that this is just how reality behaves. I.e.: the properties of the wavefunction are the "basic properties" we should care about.

Parent## (Score: 2) by Theophrastus on Tuesday July 01 2014, @04:47PM

again, i understand you're passionate, but it's the foibles of language which seems more what you're passionate about, so i'll join you insomuch to assert that a lot of "1930's thinking" contains thought that transcends my own (and would that i could get "stuck" there rather than suffer a quantum of uncertainty)

Parent## (Score: 2) by romanr on Tuesday July 01 2014, @03:49PM

He doesn't say that particles do have definite location, he says that particles have basic properties and that location isn't necessarily basic property, which is matter of opinion i would say.

Parent## (Score: 2) by romanr on Tuesday July 01 2014, @03:45PM

Thanks for clarifying your objections! I'm not defending that article or the whole summary, I just mentioned that one thing. Anyways, your notions are most insightful, I would upvote you if that was possible :).

Parent## (Score: 5, Interesting) by Anonymous Coward on Tuesday July 01 2014, @06:20PM

I think kebes' critique of the article above and here is a little heavy-handed. I'm not familiar with the Simons Foundation publication, but the article was reprinted in Wired, which although not a science magazine, is a top-notch magazine that often deals with scientific topics with high journalistic standards. The article actually covers the ideas fairly well, including descriptions of theories and commentary from important physicists. The intro gives an accurate description of the Copenhagen interpretation, which is the most widely accepted position among physicists, and yes as given in textbooks. It is weird and confusing, difficult to accept, and yet it appears to be the correct interpretation. As Seth Lloyd, physicist at MIT, is quoted in the article, "Quantum mechanics is just counterintuitive and we just have to suck it up." I think 'ghostly state' is probably a very apt description for public discussion. It also describes alternatives to that theory, primarily led by David Bohm and supported by this paper. Another alternative would be that alluded to by kebes.

Whether a measurement can be described within the context of wavefunction evolution appears to be indirectly in question here, but generally not a settled question, and seems to me to contradict the Copenhagen interpretation.

Wave functions describe everything there is to describe about a particle, but that doesn't imply that it describes everything about the particle. E.g. one wave function cannot detail/define both the position and momentum. Again, here, 'ghostly state' is appropriate.

Kebes' general description of decoherence as an explanation is probably a highly viable one, but afaik not yet widely accepted among physicists. But to say that the currently widely accepted Copenhagen interpretation is 'silly' or "1930's thinking" is factually incorrect.

My understanding has been that wave-particle duality had settled into "particles that obey QM, which is sometimes wave-like," but that effectively the particle side had won out. To very high precision, ie limited to extremely small scales, the electron for example is a point particle. But it is also observed to obey quantum wave-like principles. But see my link below to 'delayed choice' experiments, which apparently bring this question back into play. Ask any random physicist, though, and they won't be able to give you a solid answer on this.

That is because most students of physics and most physicists who study quantum mechanics never go deeper into the interpretation of quantum mechanics than the cursory explanation at the level of Griffith's Intro to QM, which is likely what kebes is using for his/her course as it's the most popular text at that level. While virtually all other areas of physics are motivated by direct insight, QM motivations are generally hand-wavy, at the textbook level, and almost all quantum texts, from Griffiths' intro on up thru advanced graduate texts, basically ignore the philosophical quandaries surrounding quantum theory and focus on how to do quantum mechanics. It's sort of like teaching/learning to ride a bicycle or swing on a swingset--the physics is fairly complex, but you can actually do it fairly easily. The practice of QM itself has been so effectual in its precise theoretical predictions and its broad application as to be evidence of its correctness.

So it is with some reluctance that I join the fray here, being a physicist that works in quantum mechanics regularly, and yet I, like so many, don't feel I have a completely solid understanding of the theoretical implications. But this also makes me doubt anyone that asserts that they understand it themselves, having only prepared lectures on introductory QM. Certainly as far as I understand it, the QM community has basically settled on one interpretation of QM, the Copenhagen interpretation, while admitting the possibility of others and noting that for the vast majority of scientific investigations, the QM interpretation itself is moot. As Griffiths says in the afterword to his text, "In light of this, it is no wonder that generations of physicists retreated to the agnostic position, and advised their students not to waste their time worrying about the conceptual foundations of the theory."

Having said this, I hope to say what my position is without implying that I speak for physicists in general or that my confidence in my position is extremely high. The original poster, martyb, borrows language from the original article, and is basically correct in his description of the story. It's almost the exact story you get in an undergraduate chemistry course--the Bohr model is introduced, depicting electrons circling an atom, and then is corrected with imprecise language, saying that what really happens is there is an "electron cloud" and the electron is actually smeared out, not just over all angles, but over a wide range in radius (technically infinite) as well, and does not possess a precise location. A similar line of description is used to explain the double-slit experiment, that particles, a single particle even, must travel through both slits in order to produce the interference pattern that we observe. You can not say that the particle went through either slit A or slit B, and therefore the particle did not have a precise location until it was observed at the sensor.

The fluid test apparently is now challenging this very argument, which is critical to quantum theory because of its simplicity and yet the apparent impossibility to explain it classically. So it is with great surprise that I read the summary and skimmed the article, although I'd heard of alternatives to quantum mechanics, probably the most well-known being David Bohm's. The implications of the present work are possibly extreme.

It's not clear whether a change in the fundamental interpretation of quantum theory would affect the general practice of quantum mechanics--my guess is that it wouldn't, but perhaps it could. The implications may only be noticed at subatomic and extremely small scales, leaving quantum theory capable of explaining most subatomic and all atomic, molecular, and solid state physics, but incapable of describing extreme fundamental considerations, just as Newtonian mechanics adequately covers a great variety of phenomena but is incomplete when relativistic or quantum scales become active. From the article, and as Bohm says, "we could easily be kept on the wrong track for a long time by restricting ourselves to the usual interpretation of quantum theory." On the other hand, some of the top physicists, such as Leggett, believe this is a waste of time, so I don't know.

But also importantly, this is a very interesting set of experiments that really does challenge the fundamental interpretation of QM. One test I would propose as an extension of the present work is to reproduce a delayed choice experiment. See http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment [wikipedia.org] . Further questions would be whether they can produce superpositions in their bound states, and entanglement/EPR paradox/Bell inequality stuff. My guess here is that they will not be able to reproduce these, but who knows. According to TFA, unfortunately it won't be soon, "an experimental test of droplet entanglement remains a distant goal."

The philosophical implications pertaining to human concerns are very important, for it resurrects Einstein's doubts of quantum indeterminacy, which we had all thought was settled and had come to terms with, though with difficulty. If indeterminacy holds, then there remains some (vanishing, thanks to recent neuroscience experiments) possibility of free will. But if the present fluid experiments and Einstein's previously held view of determinism is correct, that the evolution of nature, including all matter and non-matter, is determined, ie pre-determined and post-determined, then free will is indeed an illusion as Einstein believed.

Parent## (Score: 3, Informative) by kebes on Tuesday July 01 2014, @10:33PM

In any case, I'll happily defer to the real experts on QM theory. Such as:

Sean Carroll [wikipedia.org](CalTech) has some nice general-audience blog entries:Why the Many-Worlds Formulation of Quantum Mechanics Is Probably Correct [preposterousuniverse.com]

Does This Ontological Commitment Make Me Look Fat? [preposterousuniverse.com]

Quantum Mechanics Made Easy [preposterousuniverse.com]

(This blog post [lesswrong.com] covers some similar ground.)

Allan Adams [mit.edu]has an intro to quantum [mit.edu] course that is freely available on MIT Open Courseware, and provides a good intro (without resorting to the any Copenhagen verbiage).Max Tegmark [mit.edu](MIT) wrote a Nature commentary, Many lives in many worlds [mit.edu], that provides a general-audience into to a deterministic interpretation of QM. He also has some more technical papers on these topics (the intros and conclusions may be useful even to non-specialists):Many Worlds in Context [arxiv.org]

Parallel Universes [arxiv.org]

Yet more technical, but still interesting, are the results of decoherence (in large part from

Wojciech H. Zurek [wikipedia.org]):Decoherence, the measurement problem, and interpretations of quantum mechanics [arxiv.org]

The quantum-to-classical transition and decoherence [arxiv.org]

Decoherence and the transition from quantum to classical [arxiv.org]

Parent## (Score: 2) by melikamp on Wednesday July 02 2014, @06:03AM

Fascinating thread. I have a few general comments.

The interpretation does matter, even to physicists. It seems at least possible that the universe (or some aspect of it) is in fact a mathematical object. If it is, then it may be possible to ascertain this fact statistically. (For example, if it is deterministic, and there is a way to check the outcomes experimentally, and to re-stage these experiments many times over.) That would be an interesting discovery, and one worth making. And talking about deterministic interpretations and deterministic mathematical formalism is a basic heuristic for getting there.

As a mathematician, I don't see how a deterministic mathematical universe is more or less surprising than a non-deterministic mathematical universe. It would be far more surprising to me if the universe was discovered to be a mathematical object at all (although also deeply satisfying). Exactly what kind of mathematical object? Well, right now it looks like it is geometrical on large scales and algebraic/probabilistic on small scales (algebraic geometry is hot, incidentally), but it in the end it may turn out to be something really silly, like a finite sequence of distance matrices. All of these possibilities have exactly the same ontological status for mathematicians, and in particular, the probability theory with its perfect theoretical distributions is no less true or concrete than the integer arithmetic.

Alas, if this is the grail, then the odds are against us. Assuming that the world is mathematical, it may simply be too complicated to pin down. What if it is a bit longer than Newton's laws or the field equations? For example, it may be fully described as an algorithm (a Turing machine program) operating on a very large array of simple "particles", kind of like in the world of Newton. And this algorithm just happens to be a fancy PRNG-like gizmo with emergent macroscopic properties we are observing (so yeah, it sucks as an RNG, but because of that we have galaxies, planets and life instead of a homogenous soup). And the shortest description of this algorithm in, say, Lisp, is 10 MiB in length: a modest program by modern standards, but far more complicated than any PRNG devised so far. So a physicist may be faced with reverse-engineering a PRNG of incredible complexity, and that without even a perfect way to read the output.

The odds are against us in the sense that there are far more long programs than there are short ones, and a 10 MiB, or even a 10 TiB program is absolutely tiny when faced with the infinity of all possible programs. I don't mean to call actual odds here, only to express the cautiousness of my optimism.

Parent## (Score: 2) by kebes on Wednesday July 02 2014, @12:56PM

The Mathematical Universe [arxiv.org]

Is "the theory of everything'' merely the ultimate ensemble theory? [arxiv.org]

Shut up and calculate [arxiv.org]

On Math, Matter and Mind [arxiv.org]

The ideas he's putting forth are that:

1. The universe is, inescapably, a mathematical structure. One way of thinking about this is to say that if the universe is consistent, then it must be described by some set of non-contradictory rules, in which case one can find a mathematical formalism isomorphic to those rules. Tegmark phrases it slightly differently: explaining instead that if one accepts that the universe has independent reality (not just a product of our minds), then it must have some observer-independent description; which again implies one can find a mathematical formalism isomorphic to that description. (Read the paper for the rigorous version of this argument.)

2. If our universe is

actuallya mathematical structure, why does it have physical reality? Perhaps other mathematical structures also do? Perhapsallconsistent mathematical structures have physical reality?It's a long way from being a sound scientific theory, but interestingly Tegmark sketches out how this idea could be tested experimentally. It also has some interesting implications, e.g. that the description of the universe becomes so generalized, compact, and elegant, that its information content is nearly zero [arxiv.org].

Again, this is all just speculation at this point, but these are fun concepts to think about.

Parent## (Score: 0) by Anonymous Coward on Wednesday July 02 2014, @04:03PM

Thank you so much for your comments, those are one of the most interesting/insightful comments I've seen on any "nerdy" website about a particular topic so far. If you had some website/blog with interesting ideas/facts about QM or other topics, I'd be very happy to have it in my RSS feed :)

--

Posting anonymously, because I'm clearly OT - feel free to downvote :).

Parent## (Score: 2) by ragequit on Tuesday July 01 2014, @03:19PM

This is great and all, but are we any closer to describing any discrete set of sub-states that can decohere into a particle? Can we describe the creation of an anti-particle with a collider in quantum terms?

Unless we can, it's all just math and hand-waving to the grand majority or people.

The above views are fabricated for your reading pleasure.

Parent## (Score: 2) by HiThere on Tuesday July 01 2014, @07:59PM

I think Feynman would disagree with you. Particles are always switching modes, and personally I don't think they EVER stop, even for a measurement. My opinion is that the state vector doesn't collapse, but what is experienced is one one branch of the superposition, and that all the other branches are equally real...to those on them, including someone who's almost exactly me, but isn't quite the same me that is writing this. Different "branches" of the superposition (i.e., universe) have different levels of "probability" as indicated by "sum over histories" calculations. That those calculations are actually beyond us is irrelevant.

Now what an entity has to deal with is the branch of the superposition that it finds itself in, but that doesn't make the other branches unreal, merely not present. Parallel worlds is poetically accurate, not physically accurate. Splits happen at EACH measurement. AND branches can (improbably) merge, so that each present has multiple histories that are undecideable between. (I.e., just as one has all possible futures, one also has all possible pasts, with varying degrees of probability.)

OTOH, this is mere belief. There is no testable difference between this and the Copenhagen (Shut up and calculate) theory which one might call naive realism. And there are other models that are equally irrefutable, if not equally palatable. Everything is also compatible with "Super predestinationism", which is a solidly deterministic model that entails total determinism, with not choice at any point...from before the big bang. And to get silly, it's also compatible with Solipsism (nearly anything is). But the thing to notice is that while some of the models don't entail any predictions, others entail the same math that is used by the Copenhagen interpretation (which doesn't entail any particular math, being rather "these are the patterns we see when we go and look"). So the Copenhagen interpretation had to come before the EWG Multiworld interpretation, because it was built to match the math that the Copenhagen interpretation found. Nobody predicted that we would find what we found, so you can't use that as a guide to which is more accurate.

Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.

Parent## (Score: 2) by kebes on Tuesday July 01 2014, @08:44PM

It is indeed usually said that the Copenhagen interpretation (CI) is experimentally and mathematically indistinguishable from other formulations. But I think it's a bit more subtle than that.

CI is indeed indistinguishable from other interpretations, if one is careful about how one describes it. However, I will note that many (sloppy) descriptions of it will claim that the wavefunction collapses at some size-scale. I.e. that QM is correct for small-scale systems but that wavefunction collapse always happens well before we get to macroscale systems. They are making a physical claim of some sort of non-deterministic physical process. In these formulations, one can experimentally falsify the claim by trying to generate ever-larger superpositions. And experiments done on ever-larger systems have yet to find a point at which a superposition cannot be maintained. So these collapse claims have been falsified (no one still seriously expects to find a size-scale at which quantum effects cannot operate.)

Of course there are CI descriptions that are more careful; and essentially say that the math of QM is all perfect, but just say that you shouldn't reify any of the theory's internal quantities. Which is fair enough.

But even this may not be the whole story. Experimentally, one can keep trying to generate larger and larger superpositions. One could even imagine a radically-challenging experiment wherein a human test subject is isolated and put into a superposition, such that the external experimenters can satisfy themselves that the person is, indeed, superposed. When the person is removed from the experiment (and becomes entangled with the rest of the universe), they will only remember a single sequence of events, but the experimenters will have experimental evidence that the subject was actually in a superposition. This would essentially falsify CI and support MWI. Or rather, the results can be explained in the framework of CI only in a very strained way; whereas they are precisely what MWI predicts. Similarly, you could in principle gather enough data to go looking for the influence of other branches (which, as you note, can still improbably interfere with our branch). Finding such correlations would support MWI and again be hard to explain in CI (which claims that the other branches don't exist).

Of course these proposed experiments are probably too difficult to carry out for real. But there may be a sense in which, at least in principle, some interpretations of QM are actually experimentally different.

Parent## (Score: 0) by Anonymous Coward on Tuesday July 01 2014, @11:00PM

Now... could you sum it in layman's terms?

Parent## (Score: 3, Interesting) by dak664 on Tuesday July 01 2014, @04:19PM

The basic conceptual problem is how diffraction can occur with a single particle. In light optics one can get around this by using classical EM wave amplitudes but with quantized action transfer which can be described through mathematical constructs called "photons" whose creation and destruction have zero space-time separation (so no problem integrating the interaction probabilities over all space). It's harder to do that in electron optics where there seems a causal time-like separation between emission and absorption, i.e. each electron is "in transit".

I have not read the article but the experiment seems to show that the steady state pattern of surface topography generated by vibration (the integral over all space and time) can guide individual droplets through one slit or the other and retain the two slit pattern on the other side. Gives a nifty model of the guided wave picture. Covering one slit while the drop is in transit might lead to some insight of how a particle might couple with a evolving guided wave pattern (if such change is possible for Green's functions at all).

## (Score: 4, Informative) by VLM on Tuesday July 01 2014, @05:14PM

"who would care to explain this in layman's terms?"

I'll give it a try. Everyone else went in too deep.

In the mass media "quantum" is meaningless technobabble for "it solves all our problems" or "its new" or "its expensive" or ironically "its really big". However it actually does have a meaning and what it means to scientists is much like different ball games have different rules, there's a set of rules for really little things that unfortunately doesn't look a whole lot like the set of rules for human sized things or the ruleset for black hole sized things, unfortunately. You could get a lot of soylent news karma if you could unite all those rules successfully into one super set of rules. An a Nobel prize or two. Good luck with that.

Anyway physicists get all pissed off at "mimics" and "analogies" so when something that should run under the "human size" rules appears to run under the "tiny stuff" rules, historically they either explain it away into nothingness or get a Nobel prize by appearing on this wikipedia page (no kidding):

http://en.wikipedia.org/wiki/Macroscopic_quantum_phenomena [wikipedia.org]

So the guys in the article are doing weird things with droplets of levitating oil (which in itself is kinda cool) and pretty soon they could end up on the wikipedia page above with their own freshly minted Nobel prizes.

Or another possibility, is they might get the same prize and show up on a different wikipedia page that I'm too lazy to link to as yet another of the competing interpretations of the quantum mechanics rules, and perhaps their interpretation of their rules will be so good that will end the arguments. Or maybe not.

Or it'll all turn out to be statistical anomalies meaning nothing other than yet another pentium floating point division algo bug or they've built a really cool analog fluid computer that slowly solves quantum problems (our traditional digital computers obviously can solve the same problems, better and faster, but this is still a cool hack) In which case they'll still probably get their wikipedia article but maybe only get tenure or write a ton of interesting papers.

If you want a really good explanation instead of my half ass one, you're going to need to email bomb that XKCD Munroe guy and tell him to take his best shot in the style of the world famous "Up goer five" comic.

## (Score: 4, Interesting) by boristhespider on Tuesday July 01 2014, @07:03PM

To add a few comments to what others have written which may be of interest -- and like others I'm a physicist but no expert on quantum mechanics -- it seems that the "theory" that's going unnamed in the summary is Bohmian mechanics. An extremely important point to make about this is that Bohmian mechanics is observationally indistinguishable from quantum mechanics -- one can very easily turn one into the other. A way of finding Bohmian mechanics is to take the Schroedinger form of quantum mechanics, which is effectively based on a (complex) diffusion equation for a wavefunction, and split the wavefunction up into an amplitude and a phase. (The so-called Madelung representation, psi = A exp(iS), where both A and S are real numbers.) Following this through quickly leads to two equations. One is simply fluid continuity, which states that the density of a fluid is conserved; that density is A^2. The other is an equation for S, which can be interpreted as a Bernoulli equation (or, more obscurely but more usefully theoretically, a Hamilton-Jacobi equation). From this equation we can identify the potential that this fluid is moving in -- and it's modified from the classical situation purely and only by a non-local term depending on the derivatives of the density which is sometimes dubbed "the quantum potential".

Viewed in this representation, this "quantum potential" is the

only differencebetween quantum mechanics and classical mechanics.Bohmian mechanics is ultimately an interpretation that takes this seriously: start with a classical situation, postulate the quantum potential through some rapid hand-waving, and if you choose to work with a wavefunction combining together your Bernoulli equation and your continuity equation then that's your lookout. (A consequence of developing this fully is that Bohmian mechanics is a hidden-variable theory.) The more usual interpretation is that this is an interesting and sometimes useful curiosity.

http://plato.stanford.edu/entries/qm-bohm/ [stanford.edu] might be of interest to some -- section 5 is effectively what I've tried to describe here. It's also discussed on Wikipedia, http://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory#Derivations [wikipedia.org]

## (Score: 1) by JNCF on Tuesday July 01 2014, @10:23PM

It seems odd to me that TFA didn't even make passing mention of the many-worlds interpretation of quantum mechanics, which is also a fully deterministic theory. In the Copenhagen interpretation, when a particle interacts with something the universe selects one of the possible courses for the particle to take. In the many-worlds interpretation, the universe selects

allpossible courses for the particle to take. To human observers stuck in thing, it appears as if it only went the one route. I once bought a lottery ticket with quantum generated numbers, and in this universe it appears that I lost a dollar. But if an omnipotent observer were to look across the multiple worlds, it would appear as if I had lost way more money than that (lotteries obviously don't pay out on average, unless you play at just the right time).To my uneducated eyes, it seems that the Copenhagen interpretation is a silly attempt to make the universe work the way we expect it to. We're familiar with the idea of one world, and we don't like shrugging off familiar notions. We were familiar with a flat world, too. And a world with stars that orbited around it. If science has anything to tell us, it's that the universe is a damn strange place to live in. Don't expect the expected.