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Oil droplets guided by pilot waves do not give rise to double-slit interference
- clydesdale 8y agoSo, pilot wave theory remains a strong intuitive model, by confirming an inability to perfectly predict the future state of a system of quantum events.
- soveran 8y agoAll the paradoxes disappear if we use Quantum Field Theory instead of Quantum Mechanics. I would really like someone with deep knowledge on Quantum Theory to explain if something is wrong with a theory that otherwise makes a lot of sense to me. A good read on the topic is the paper "There are no particles, there are only fields" — https://arxiv.org/pdf/1204.4616.pdf https://arxiv.org/pdf/1204.4616.pdf
- platz 8y agoYou can say that the only thing that exists is the quantum wave function, as what basically this paper says (particles are epiphenomena). That is basically hard-line Everettianism e.g. many worlds. There are still problems. QFT does not explain gravity very well either. The paper claims "it's neutral on the interpretations" - it is not. You have the most senior research professor of physics at caltech admitting there are problems still - there are of course physicists that insist they have the correct answer or interpretation - the hard part is convincing enough physicists to agree with them, which they universally do not agree.
- kgwgk 8y ago> You have the most senior research professor of physics at caltech What is the ranking of seniority of research professors at Caltech? Are you implying that a research professor is somehow better than a “regular” professor?
- hexane360 8y ago>Are you implying that a research professor is somehow better than a “regular” professor? Probably when it comes to understanding and forming opinions on cutting edge research. . .
- kgwgk 8y agoThe only reason why that particular research professor is not “just” a professor is that he was denied tenure at the University of Chicago.
- soveran 8y agoI don't think the paper assumes a many worlds interpretation.
- platz 8y agothat's what it claims, but that is the only way to make sense of "particles are epiphenomena" + "Thus the Schroedinger field is a space-filling physical field whose value at any spatial point is the probability amplitude for an interaction to occur at that point." it is saying that the only thing that exists is the quantum wave function the only theory with a hope of credibility/coherence that says the only thing that exists is the quantum wave function is many worlds.
- abdullahkhalids 8y agoSurprisingly, physicists are very much aware of the field nature of all "entities" in the world, having invented QFT themselves. Even more surprisingly, popular journalistic explanations simplify things considerably, making it seem that the thoughts of physicists are much less refined than they really are. To complete the trifecta of surprises, in the refined thought process of us physicists, using QFT, many problems and paradoxes of interpretational nature or otherwise remain with quantum theory that need to be resolved.
- perl4ever 8y agoRegarding "in the refined thought process of us physicists...many problems and paradoxes...remain". It seems to me that a true paradox in physics must mean a theory provides at least two different incompatible predictions for a given physical situation. Given the success of the Standard Model, that surprises me. Do you have an example?
- whatshisface 8y agoThe use of the word "paradox" in physics usually means any conclusion that is considered unacceptable or unnatural for any reason, even intuitive. In logic there are no paradoxes, only contradictions. As far as we know there aren't any contradictions in the standard model, but there are plenty of suspicious conclusions that we would like to see resolved either with greater understanding or a better theory.
- soveran 8y agoDid you read the paper I linked to?
- abdullahkhalids 8y agoI did not read the whole thing, but I skimmed it. Its not a new-results type of paper. It is just collecting the works of other people and being careful about the language used. I have grappled with some of these issues/formalism/language in my own research as have many other physicists over the decades. The purpose of this paper is to argue that "Textbooks need to reflect that fields, not particles, form our most fundamental description of nature. This can be done easily, not by trying to teach the formalism of QFT in introductory courses, but rather by talking about fields, explaining that there are no particles but only particle - like phenomena caused by field quantization." Notice that he is talking about teaching/talking/explaining. It is a for-teachers paper, not a for-researchers-working at-the-cutting-edge-of-fundamental-physics paper. And its nothing new. I taught an introductory level course on quantum mechanics recently and I refused to use the words "particle" or "wave" at any point in the course because I think they are confusing. I talked instead in terms of wavefunctions which is just an easier word for fields - at least as far as undergraduates are concerned.
- v_lisivka 8y agoQuantum Field Theory in plain English means "3D Array of Integers Theory".
- mehwoot 8y agoWhy does this matter? Does anybody seriously question whether the basic math can work? So somebody found a nice parallel between pilot wave theory and another physical phenomenon, but then the parallel wasn't as strong as thought. This experiment is the equivalent of arguing that light isn't a particle because your tennis ball doesn't bounce off the wall the way you thought it would. When I saw the droplet experiments, I thought "that's cool, but it doesn't prove anything about pilot wave theory because the arguments are over much deeper things than what this is demonstrating". Debunking it is just as meaningless. The people who actually know about this stuff are arguing over determinism and non-locality and what not. I thought oil droplets are just a nice way to introduce people to the concept. Disclaimer: I don't really know anything about any of this
- spindle 8y agoThat's absolutely right. There's nothing surprising in this article, and it doesn't provide any new support to any theory.
- gmueckl 8y agoSo.you are essentially saying that that oil droplet on water analog cannot be treated as an analog computer (in every sense of the word) for pilot wave theory?
- mpweiher 8y agoWell, I think the opposite result would have been very interesting/surprising. So I think it's a good experiment, and it's good to publish negative results. The subhead seems a tad sensationalist. If interference had been shown, it would have suggested strongly that this can happen at the smaller scale as well, and that it didn't is probably disappointing for those that hoped to show it in the analogy. Not sure how it "crushes" those theories.
- jobigoud 8y agoMaybe that's how we clickbaitify the null hypothesis and save science.
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- Lerc 8y agoSo, am I right in thinking that we have. 1. Theory X hypothesizes Q 2. Phenomenon Y models theory X 3. Phenomenon Y does not demonstrate Q Surely there would be an insurmountable burden of proof on 2. Similarity does not mean identical. For any Y claiming to be the same as X, why can't it be rebutted with a "No it isn't" Proving that they are the same would be a different thing altogether but if as the article suggests X is not fully defined, it strikes me as impossible to prove. It just ends up in the not-falsifiable bin.
- dumbfoundded 8y agoThat's a fair observation. Though, I think the thought experiment to about the distance between the two slits as irrelevant to QM more concretely disproves the pilot wave theory. Most physicists when asked about QM will just say that this is a useful model to predict the outcomes of experiments. In fact the most successful model, ever. The magic that happens in the middle is currently untestable and thus uninteresting beyond philosophy. The problem with determinism is that it introduces more complexity to the model without improving any accuracy. Moreover, it doesn't help us predict the outcome of any experiments. Even if this experiment was successful, who cares? Does it change the math or predictions? Science works in a very simple way. We have evidence about how the universe works. We make models to explain that evidence. The models also make predictions about new evidence that we would expect to see. New evidence appears and either confirms or limits the domain of the model. Basically nothing but gravity has limited the domain of QM.
- naasking 8y ago> Though, I think the thought experiment to about the distance between the two slits as irrelevant to QM more concretely disproves the pilot wave theory. This sort of experiment does not disprove pilot waves. > Science works in a very simple way. We have evidence about how the universe works. We make models to explain that evidence. The models also make predictions about new evidence that we would expect to see. New evidence appears and either confirms or limits the domain of the model This is a very anemic view of the scientific process. Scientific theories have predictive and explanatory power. You described the process covering only the former, but the latter is critical for advancing theory. For instance, without Bohmian mechanics John Bell probably would never have developed Bell's Theorem and all the subsequent no-go theorems which have dramatically improved our understanding of quantum foundations. Theories that provide a mental framework for thinking about problems guide you in devising new experiments. Theories with no explanatory power provide no meaningful framework within which to devise new experiments.
- pg_bot 8y agoI was thinking about the double-slit problem the other day, and was trying to make connections to any other phenomenon that exists in the natural world and I think I came up with one. In conditional probability theory, there exists something called the boy or girl paradox. The paradox shows that the likelihood of an event can be drastically affected by how you know even seemingly innocuous information. I think that observation of the atoms passing through the slit is affecting the search space for the other atoms in such a way that we currently do not understand. This observation while seemingly innocuous has a drastic affect on the distribution which would explain why we see such confounding results. It follows the same logic as this other naturally occurring phenomenon so I think its an avenue at least worth exploring. An example of the paradox would be if I told you that my neighbor has 2 children and at least one of them is a boy. If I asked you what the probability that their other child is a girl, normally the result would be 2 / 3, but if I know one child is a boy because I spot him in front of a tree then the odds his other child is a girl drops to 1 / 2. [0]: https://en.wikipedia.org/wiki/Boy_or_Girl_paradox https://en.wikipedia.org/wiki/Boy_or_Girl_paradox
- im3w1l 8y agoThe boy or girl paradox does appear in physics but not like this. Distinguishable particles behave like "older child is a girl", while indistinguishable particles behave like "at least one child is a girl"
- everdev 8y agoIt's more like seeing one boy actually impacts the gender of the second child, which is why the quantum experiment is so mind boggling. It doesn't seem to have any resemblance with classical physics and only makes sense in quantum physics.
- pg_bot 8y agoThat's exactly what the paradox states. Seeing one boy does affect the gender of the second child.
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- User23 8y agoFor some background on pilot waves: https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory. Also from the same source, a couple years back: https://www.quantamagazine.org/pilot-wave-theory-gains-experimental-support-20160516/ https://www.quantamagazine.org/pilot-wave-theory-gains-exper...
- inciampati 8y agoThere is recent research on photons (rather than bouncing oil droplets) that backs up the Bohmian interpretation. "Experimental nonlocal and surreal Bohmian trajectories" http://advances.sciencemag.org/content/2/2/e1501466 http://advances.sciencemag.org/content/2/2/e1501466 I am not sure if the different QM interpretations are only a matter of taste in terms of all predictions. These surreal trajectories are seen as nonsense under the Copenhagen interpretation.
- simonveith123 8y agoTop content http://go.simonv.44409.digistore24.com/ http://go.simonv.44409.digistore24.com/
- m12k 8y agoI'm a bit sad that they couldn't reproduce the double slit interference pattern. I'm still holding out hope that we'll eventually develop a model of reality where the apparent indeterminism of quantum mechanics can be explained by currently unobservable interactions in higher dimensional space (such as the space described here: https://www.quantamagazine.org/physicists-discover-geometry-underlying-particle-physics-20130917/ https://www.quantamagazine.org/physicists-discover-geometry-... )
- msslx 8y agoAt least locally, there are no hidden variables (e.g., in higher dimensional space). You might have a look at Bell's work on hidden-variable theory: https://en.wikipedia.org/wiki/Hidden-variable_theory#Bell%27s_theorem https://en.wikipedia.org/wiki/Hidden-variable_theory#Bell%27...
- whatshisface 8y agoWhat you're describing has been desired by many (including Einstein). However, John Bell more or less proved it impossible[0] in a landmark, sweepingly general result. He would have won a Nobel for it if he had lived long enough. On the other hand, if you are willing to accept superluminal messages and also unobservable mechanics, there is always the pilot wave interpretation[1]. The fluid analogy is disappointing to see go but pilot wave theory lives on. [1]https://en.wikipedia.org/wiki/Pilot_wave_theory https://en.wikipedia.org/wiki/Pilot_wave_theory [0]https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem Edit: fixed order of references.
- twtw 8y agoFYI your references are swapped.
- m12k 8y agoThanks for the link to Bell's Theorem (I recalled there being a result like that, but didn't remember the details of it). If the hidden variables really are in a higher dimensional space, then maybe superluminal communication (in our observable dimensions of space) isn't off the table either? But that comes with its own can of worms that would have to be taken care of as well.
- twtw 8y agoBohm's pilot wave theory is interesting to me not because it is so intuitive or tasteful or something, but because it works without sacrificing realism, and thus demonstrates that the Cophenhagen interpretation (neither local nor real) claims strictly more about the nature of the universe than is required by the evidence we have. Nonlocality is established by experiment, non-realism is not. In my experience, this tends to be underappreciated (or I'm misunderstanding - please teach me if so). I personally favor epistemological interpretations, in which the wave function models our knowledge, and the universe operates via an as-yet-unknown dynamics. Wave function collapse on measurement isn't weird anymore if the wave function represents your knowledge of the system. Thinking about it this way makes "shut up and calculate" work nicely in my head.
- eggie 8y ago> but because it works without sacrificing realism, and thus demonstrates that the Cophenhagen interpretation (neither local nor real) claims strictly more about the nature of the universe than is required by the evidence we have Nicely put! > Wave function collapse on measurement isn't weird anymore if the wave function represents your knowledge of the system. To me it is intuitive if you consider that the wave function of the small entity is interacting with the much larger (and more specific) wave function of the observing apparatus. I never understood the mystical aspect with which this was treated in the typical explanations of the Copenhagen interpretation. And I would also appreciate the guidance of someone with a better understanding of the physical theories, if my stated perspective is confused.
- Gravityloss 8y agoYeah it's also why Schrödinger's cat isn't a real problem. Most misunderstood thing.
- naasking 8y ago> I personally favor epistemological interpretations, in which the wave function models our knowledge These have been largely ruled out via no-go theorems [1]. [1] https://en.wikipedia.org/wiki/PBR_theorem https://en.wikipedia.org/wiki/PBR_theorem
- snarfy 8y agoI don't understand why non-locality is a problem. Fields are non-local. If particles are point-like, fields are volume-like and permeate all of space. Problems like spooky action at a distance aren't really problems if there is no distance from the field's point of view.
- danenania 8y agoWhy isn't there distance from the field's point of view? Isn't the field spread throughout space?
- snarfy 8y agoBut it's still considered one field, not many individual fields at each point. That's why I called it volume-like. The electric field of the universe doesn't have a position. It has a volume.
- fjsolwmv 8y agoFields are not nonlocal. Interactions in a field propagate at the speed of light or force-carrying particles. This is one of Eintein's major contributions to physics, that nothing travels faster than light.
- snarfy 8y agoI guess I'm arguing it's more a change of the field, not something propagating in it. Faster than light restrictions do not apply to space itself which, e.g. can expand faster than light. The electric field is a property of space. It's strength and properties do not depend on spacial coordinate. When two particles are entangled, maybe instead the field is 'twisted/warped' at those particles. Entangling particles alters the field, not the particles.
- phkahler 8y agoHas anyone done the double slit experiment with the long wall before the slits? I'm not entirely convinced it still works unless it has been demonstrated.
- eggie 8y agoThat would be something to directly ask Prof. Bohr who's mentioned in the article.
- naasking 8y agoI don't think this is all that surprising to anyone. The "pilot waves" in the oil bath aren't superluminal, so of course they don't correspond with perfectly QM pilot waves, ie. they will only correspond in scenarios where the non-locality doesn't matter. Edit: the article actually agrees with this, so it's hyperbolic all the way through except this critical passage: > In a quantum reality driven by local interactions between a particle and a pilot wave, you lose the necessary symmetry to produce double-slit interference and other nonlocal quantum phenomena. An ethereal, nonlocal wave function is needed that can travel unimpeded on both sides of any wall.
- branksy 8y ago> Unsustained by the particle or droplet, the wavefront disperses long before reaching its slit, and there’s no interference pattern. The Danish researchers verified these arguments with computer simulations. Wait, what? From what I've always understood, the math behind de Broglie-Bohm interpretation results in the same exact results as the Copenhagen interpretation. It shouldn't be possible for any "computer simulation" to disprove it, by definition. This article feels 1) pointless and 2) like it has an agenda. Oil droplets are a macro-scale approximation of something on the particle level where we already know the math works. This doesn't disprove anything, any more than doing experiments with rubber sheets and basketballs lets you disprove the general theory of relativity. > crushing a century-old dream that there exists a single, concrete reality. This is just sensationalist, cheap journalism. I expected far better from Quanta Magazine, and I'm disappointed in them. I've enjoyed many of their articles in the past, but I'm not sure I can trust them editorially any more if they print something so obviously incorrect as this article.
- andrewla 8y ago> Wait, what? From what I've always understood, the math behind de Broglie-Bohm interpretation results in the same exact results as the Copenhagen interpretation. The de Broglie-Bohm interpretation is not the same as the pilot-wave theory, which was never fully fleshed out. de Broglie-Bohm is valid and makes the same predictions as the standard interpretation, but as I understood it, has never been generalized to the relativistic versions of the standard theory. That is, there is no de Broglie-Bohm version of quantum field theory. This is discussed in the article; the de Broglie-Bohm interpretation relies on a global pilot wave, which has non-locality issues that pilot wave theory hoped to avoid. > It shouldn't be possible for any "computer simulation" to disprove it, by definition. Here I believe they are disproving the idea that the oil droplets riding the pilot waves cannot result in the double-slit interference pattern, using standard fluid mechanics (which appears to be Tomas Bohr's area of expertise).
- potiuper 8y ago> The de Broglie-Bohm interpretation is not the same as the pilot-wave theory, which was never fully fleshed out. Most contexts (https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory) define pilot-wave theory and the de Broglie-Bohm interpretation as the same. de Broglie himself also proposed a specific pilot-wave theory that is not valid (see article). When referring to a "pilot-wave" theory it is helpful to state specifically who the author is in order to resolve any likely confusion, which this topic usually seems to involve. > has never been generalized to the relativistic versions of the standard theory Quantum field theory generalizations( https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory#Quantum_field_theory" https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory...) do exist.
- gpm 8y ago> droplets were seen to tunnel through barriers If true, one wonders if you could use this to build a d-wave like annealer.
- GregBuchholz 8y agoDoes anyone have a link to a video of the oil drop tunneling experiment? https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.102.240401 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.10... (like https://www.youtube.com/watch?v=nmC0ygr08tE https://www.youtube.com/watch?v=nmC0ygr08tE)
- mncharity 8y ago"Visualizing pilot-wave phenomena: the $60 rig" http://math.mit.edu/~bush/?p=3230 http://math.mit.edu/~bush/?p=3230