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Droplets and pilot waves vs quantum mechanics

I've been overwhelmed by the sheer amount of idiocy about quantum mechanics that we may encounter in the would-be scientific mainstream media. A new wave of nonsense claiming that someone overthrew quantum mechanics is appearing on a daily basis. Please, don't send me links to this stuff, there has been just way too much of this worthless trash that is getting worse and worse.

The first individuals who would start campaigns against theoretical physics a decade ago – various Shmoits – should have been given a proper thrashing at that time so that they wouldn't climb out of the sewerage system again. We have failed miserably and just like I predicted, similar anti-science compaigns are increasingly strong, increasingly stupid, and attacking increasingly fundamental (and increasingly elementary) layers of modern of science. It was "just" string theory 8 years ago, now it is quantum mechanics. By 2020, heliocentrism is sure to be under attack, too.

About 8 people sent me links to this story about the droplets "proving" that quantum mechanics isn't based on probabilities and is governed by something like the pilot wave theory.

What If There's a Way to Explain Quantum Physics Without the Probabilistic Weirdness? (Colin Schultz,

Have We Been Interpreting Quantum Mechanics Wrong This Whole Time? (Natalie Wolchover, Quanta Magazine)
The story is that Bush et al. at MIT did some playful experiments with droplets and the conclusion is supposed to be that this strengthens the case for de Broglie's pilot wave theory.


All of Nature is governed by mathematics. So we encounter mathematical objects and equations everywhere. Even some types of ordinary or partial differential equations are recycled hundreds of times, in very diverse situations.

A person who hasn't been sleeping since the time when she was an embryo must have noticed this omnipresence of mathematics and is no longer shocked by it. In fact, such a sane person has improved her resolution and precision a little bit so she is able to see differences.

One may surely design some objects that obey equations not too mathematically different from those that Louis de Broglie (and 25 years later, if we just pretend that plagiarism is OK, David Bohm) proposed to replace proper quantum mechanics. The waves in the model may propagate similarly.

In fact, this "modeling" and "visualization" has a rather long history: George Francis FitzGerald has constructed a working model of the "luminiferous aether" emulating Maxwell's equations (partly inspired by James Clerk Maxwell's own engineering sketches of the gadget) out of wheels and gears. Mechanics flourished in the 19th century. These successes couldn't change anything about the fact that the luminiferous aether doesn't exist. One would think that people learn some lesson. On the contrary, a vast majority of the people learn nothing at all and they are doing much more stupider mistakes than the people in the 19th century.

The problem is that there are also a huge differences that you shouldn't overlook unless your brain is completely messed up. While the wheels-and-gears model of the aether pretty much did what it was supposed to do, there are differences both in the physical interpretation and in the mathematical details of the two situations here – droplets and the wave function. You might say that the former (physical, interpretational, conceptual differences) are more profound but once you learn to think quantitatively, you actually see that the latter (the mathematical differences) is equally profound and, in fact, equivalent.

The physical, conceptual differences between any quantities describing droplets on one side and the wave function on the other side are clear. The former are observable – you may actually measure what the shape of the droplet looks like; you can't measure the wave function by any apparatus, at least not in a single repetition of the experiment. The former has an objective interpretation; the latter has a probabilistic interpretation, and so on. The wave function just encodes all the probability distributions for actual observables – but the wave function isn't and can't be one of them.

There are also important enough mathematical differences.

In Schrödinger's picture (and even in the misguided equation controlling the "pilot wave" proposed to supersede quantum mechanics), the wave function obeys an exactly linear equation\[

i\hbar\frac{\partial}{\partial t} \ket\psi = H \ket\psi.

\] It is very important that all such equations are exactly linear and the actions of observables and operators expressing transformations are exactly linear. In combination with Born's rule, the exact linearity is required by the laws of "pure logic" expressed using the probability calculus, e.g. for the fact that\[

P(A\text{ or }B) = P(A)+P(B) - P(A\text{ and }B).

\] Note that this equation is linear in the probabilities and it has to be so for a simple reason. The probabilities are just ratios of repetitions of an event in which a condition is satisfied. The binary operators "OR" and/or "AND" correspond to the intersections and unions of sets of these repetitions of events and the equation above is nothing else than the equation dictating the number of elements in a union of two sets (divided by the total number of repetitions of the event). You just can't modify these rules, not even by a tiny amount.

All the experiments we have ever made are consistent with the exactly linear evolution of the wave function and the exact linearity of all the operators encoding observables – any observables. But once again, you don't really need to make experiments. This is a matter of elementary consistency of quantum mechanics.

On the other hand, the shape of droplets is encoded in observables, e.g. in functions \(x(t)\) of time or in the fields \(\varphi(x,y,z,t)\) etc. Classically, they are \(c\)-number-valued functions of time (or spacetime) coordinates. Quantum mechanically, these are observables – i.e. linear operators on the Hilbert space.

If you look for the most direct quantum counterparts, the classical equations of motion are most straightforwardly translated to the Heisenberg equations of motion for the operators in the Heisenberg picture of quantum mechanics. And this evolution of the classical quantities or the quantum operators is pretty much never linear in the operators. Linear equations of motion would mean that the system is non-interacting and completely uninteresting. Using the arguments based on naturalness, or the Gell-Mann totalitarian principle, if you wish, pretty much every higher-order (nonlinear) term may appear and will appear in the equations of motion.

So even if you forget about the completely different interpretations of the wave function and the shape of droplets, there is a difference (well, many differences, but I chose this one) at the purely mathematical level. The equations governing the evolution of the wave function must be exactly linear and there can't be any debate about it because it's a matter of consistency. The equations governing the evolution of the shape of droplets are almost certainly nonlinear because there is no general constraint that would ban the nonlinearity, and they are therefore 99.999...% likely to occur. You may find situations and approximations in which the nonlinearities are small or the nonlinear equations emulate some linear ones for other reasons, but fundamentally they are very different.

So these things may be similar at the level of containing some remotely similar differential equations but as soon as your resolution gets better than mine is after 10 pints of beer, you should be able to see that there are profound differences both of mathematical and physical nature.

I really can't understand what drives people to saying and even writing these breathtakingly childishly stupid things. If you have a slightly retarded 6-year-old baby, it may ask you why cars move. And you explain to her that there is an elephant inside the car.

Well, sometimes it may be true but what you mean is that there is an elephant inside the motor who is pushing the wheels using its trunk. That's cute – well, the child is perhaps cute which is why everything she likes is cute – but for an adult person, it's just stupid. Even if a child is satisfied with the explanation, it clearly doesn't work. It cannot satisfy a person who is able to ask why and creatively test the ideas that are being pushed into her ears.

The motors are just not being built out of elephants.

And the situation with the wave function is completely analogous. It demonstrably and obviously has nothing to do with the evolution of droplets of any kind. The probabilistic character of the wave function isn't a topic for deep philosophical debates or research. One can make elementary and trivial observations to directly and instantly see that the wave function has to be interpreted probabilistically, otherwise it has nothing to do with Nature! The probabilistic character of the wave function – so different from the evolving droplets – is an empirical fact that is trivial to prove by some of the simplest and fastest observations we can make. Just see that the double slit experiment creates individual dots while macroscopic droplets don't. In fact, the wave function has nothing to do with the evolution of any dynamical variables – observables – in any physical system in the world because the wave function is – importantly enough – not an observable.

There are way too many things in the articles that drive me up the wall. While a few physicists – e.g. Anthony Leggett – are allowed to mention that this whole droplet-quantum "work" is worthless šit, there are many others who positively hype it, including some favorite physicists of mine. Their affiliation often happens to be the same as that of Mr Bush. But a bias that is this obvious is just bad. Note that I haven't mentioned the name of the particular physicist who disappointed me, in order to keep the name confidential, but to promote this kind of šit just because they do it at MIT is outrageous, Frank! ;-)

Even if I subtract the pathetic "research" and the disappointing support of it by some well-known names, there are just so many things that are so insultingly stupid, manipulative, and contradicting the very essence of the scientific method. Wolchover's title is
Have We Been Interpreting Quantum Mechanics Wrong This Whole Time?
It's terrible how she talks about "we". She surely doesn't belong among the physicists who have something sensible to say about these matters – she is just an inkspiller. She has no clue what quantum mechanics actually is, and she (just like 99+ percent of the mankind) has never had such a clue – the whole time. But even physicists who have been talking about these matters are in no way "we". Clearly, quantum mechanics was too hard and too new for some physicists from the beginning – including a revolutionary named Einstein – so these people clearly didn't belong among the "we" of the people who properly understood quantum mechanics. But even the people who effectively understood quantum mechanics would find some differences in their "interpretation" of quantum mechanics – and the most reasonable ones would point out that the very phrase "interpretation of quantum mechanics" is silly. Quantum mechanics is the new theory so once we describe its rules and axioms, we know them and there's nothing to interpret. On the contrary, we may apply these rules to some situations and derive certain particular insights, for example the classical limit. In this sense, it's the "classical physics" that may be interpreted within quantum mechanics but quantum mechanics doesn't need (and doesn't allow) any additional "interpretations". You either understand the theory or you don't.

More generally, science just doesn't work in this collectivist way, and it will never work like that. So if some hopeless morons decide that the probability of the pilot wave theory has increased because they have played with droplets like retarded 6-year-old children, it will still be true that "we" continue to know that the paradigm is as wrong as it was in 1927.

I wanted to write a rant so that I may finally close the two insultingly stupid pages about the "droplets of quantum mechanics". I hope that now I will feel a bit lighter and please don't bother me with this junk again.

This blog post won't be proofread again because this whole theme is an amazing waste of time.

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reader Gene Day said...

Yes, it is a BIG waste of time :-(

reader Holger said...

Well, obviously QM is commonly regarded incomplete because it simply doesn't tell us what we need to know about nature in order to come to a deeper understanding about its basic mechanisms. "Probability" is not a mechanism, it is just an outcome, a consequence of something we don't yet understand.

Take the case of a free neutron: A neutron inside a lab is objectively there, it can be "measured" and manipulated, until it suddenly decays. Now, why did that particular neutron decay after, say, 10 minutes, while another sample decays after 15 minutes? QM yields the probabilities for this decay process, but it does not predict when exactly a selected neutron is going to decay. This is a shortage that has to be overcome. A physicist always has to ask why, he should never be satisfied with "a set of rules" which yield some probabilities. This would not be physics, just bookkeeping. We need to go deeper into these mechanisms and thereby understand what exactly makes that particular neutron decay at that particular time. QM is only an intermediate step toward that goal.

reader davideisenstadt said...

thanks lubos, for letting me know what you think.
sorry to have burdened you with BS.
mea culpa

reader Luboš Motl said...

No problem, David, if you didn't do it, I would still have gotten 7 copies of that. ;-)

reader AJ said...

I saw these dancing droplets in an episode of Through the Wormhole and wondered if your response would be "Crackpottery!". You didn't disappoint :) I imagine that many concepts presented in this series fall into the same category, but I still find it entertaining.

reader Dilaton said...

QM is QFT in 1 time and 0 space dimension.

reader Federico Barocci said...

Hi Lubos, what do you think about the following. John Bell states in his book “Speakable and unspeakable in quantum mechanics” Chapter 14, page 115, that “the guiding wave,
in the general case, propagates not in ordinary three-space but in a multidimensional-configuration space is the origin of the notorious 'nonlocality' of quantum mechanics. It is a merit of the de Broglie-Bohm version to bring this out so explicitly that it cannot be ignored.” If I understand him well, Bell also argues that we should get rid of the idea of “particles” or droplets described, as you say, by almost certainly nonlinear equations. The only valid way to speak about “particles”
is by using their multi-dimensional wavefunction ground state. Then Bell refers to Ghirardi, Rimini and Weber: “The idea is that while a wavefunction normally evolves according to the Schrödinger equation, from time to time it makes a jump. Yes, a jump!”. Now, these “jumps” are “reduced” or “collapsed”
wavefunctions that we observe as “particles” in ordinary 3d space. And further on page 209: [Schrödinger] would have liked the complete absence of particles from the theory, and yet the emergence of 'particle tracks', and more generally
of the 'particularity' of the world, on the macroscopic level.” Particles, in the end, are the smallest concentration of energy incorporated into the wave, thus, they are itself collapsed waves described by the exactly linear evolution of the multi-dimensional wavefunction. I thought that the experiments carried out by Couder et al. could be nice approximations of the underlying ground state.

reader Dilaton said...

It is not only that more and more elementary established knowledge gets attacked in the course of time.

Also, to me it seems that first the nonsense appeared "only" in the popular "science" channels (which made physicists wrongly ignore it), but in the course of time it also started to appear at places one should be able to trust that they are free of crap, such as "peer-reviewed" journals for example.

reader Shintaro said...

I think the problem at hand is you're assuming there actually is a reason the neutron decays at some particular time, and that the electron and anti-neutrino have to go off in particular directions when this happens. And there's no reason that there actually should be such a reason. Maybe Nature really is random and that there are uncaused events. Why shouldn't there be?

If we had good reason to suspect that apparently identical neutrons were actually different, and that there were an underlying cause for different neutrons decaying with slightly different lifetimes, then it'd be a fair question to ask what these underlying differences were, and how they effected different decay times. But the fact of the matter is we have no reason to think any neutron is different than any other neutron. (And saying "well they must be different because they decay after different lengths of time" is just question-begging; it's the very claim that different outcomes require different initial conditions that's being contested, so you can't use your claim as a premise.)

reader W.A. Zajc said...

I can’t resist further beating this dead horse. If I correctly understand the experimental set-up, the droplets exhibit the “interference” pattern only after some period of time required for the putative pilot waves to establish the two-slit interference pattern. This is fundamentally different than the quantum mechanical case, where the interference pattern develops even when the flux of particles is so low as to guarantee that there is (at most) one particle in the apparatus at any given time. I therefore assume that if one starts with a quiescent apparatus, introduces one droplet, and then waits until the “pilot wave” has damped out before introducing the next droplet, you will see some a mish-mash rather than a simulation of an interference pattern. To argue that this experiment has any implications for QM or any ability to improve our understanding of how QM works is, for this reason and for all the other reasons Lubos has delineated, profoundly wrong-headed.

reader tomandersen said...

That's not how Couder's experiments work. The pilot wave never dampens out, as there is energy coming into the system to keep the model alive. (Whole plate vibrates near the Faraday instability limit).

You get thus get interference with one particle at a time.

reader Gene Day said...

There is no deeper understanding and there never will be. God does, indeed, throw dice. Get used to it.

I happen to be a physicist, Holger, and it is preposterous for you to tell me what I should or should not be satisfied with. Until you free your mind of deterministic thinking you will be forever lost in the woods.

Physics is precisely a set of rules that yield probabilities. If you don’t like it you can follow Feynman’s advice and go to another universe. This one is quantum mechanical to its core.

reader W.A. Zajc said...

The pilot wave never dampens out, as there is energy coming into the system to keep the model alive.

Ummm… that’s exactly my point.

Let me try the following: when in high school, I cut class one day to go see the then new John Hancock tower in Chicago (this was an epic cut, as I lived about 150 km from Chicago). From the observation deck on the 92nd floor, I could see waves on Lake Michigan impinging on two openings (slits) in the breakwater that defined the Chicago harbor. There was a beautiful two-slit interference pattern. Now if on shore I recorded the location of every bit of flotsam and jetsam (aka piece of crap) and found it correlated with the interference pattern of the waves, would that provide new insights into quantum mechanics? The only difference I can see in Couder’s experiments is that the droplets (aka piece of crap) are auto-generated by some process (undoubtedly non-linear, as Lubos has emphasized) that is connected to the “pilot waves”. But there is nothing fundamental going on here...

reader Hacienda said...

A: If QM were as easy as the pilot wave theory is making it out be, then Niels Bohr is an idiot.
B: Niels Bohr was not an idiot.
Therefore pilot wave theory is not QM.

reader jon said...

The pilot wave is an attempt to get around superposition. But how can we be sure that even though there is superposition, there isn't still a deterministic interaction with some otherwise undetected deterministic process that triggers the collapse? That would be meaningless speculation if there was no way in principle to observe it, but there could be ways. To probe space for such a process you would need an extremely large number of interaction in a small volume, but perhaps some observed anomalies could be interpreted as a result of such a model.

reader Peter F. said...

I get your well put point - to me put well by crucially including the word "sometimes".

Personally, I would have nothing to say/nothing to 'contribute' (am referring to a 'contribution' that tends to fall on deaf ears or be overwhelmingly refused, rejected, or recoiled from) if I were not focusing and betting on the tiny chance that aiming to explain a certain emergent evolution related aspect of What Is going on with words might be worthwhile.

Am referring to an aspect of 'what there is to recognize', one which is recognized with optimally percEPTive potency (not adaptive potency) utterly rarely because of how 'the law of quantum-level produced probabilities played out' {and will as a matter of principle play out in any universe similar enough to ours - i.e. ~ any that forges a phylogeny of fauna} in the form of a sub-principle of Natural Selection that is not much less simple and heuristic than Darwin's super-principle.

reader Luboš Motl said...

Dear Federico, our world is relativistic and quantum particles have to be described by the so-called quantum field theory - or anything that is a "specialized extension of it", I mean string theory.

And in quantum field theory or in those, the statements you quote are easily seen to be wrong. All of them. The particle-position basis isn't even well-defined in general and it is extremely general and non-fundamental.

And particles are in no way "the most compressed quantum waves" one may wave. Quite on the contrary, when we talk about particles that are as well-defined as possible, their wave function must be much more spread than on the Compton wavelength corresponding to the particle.

If you try to compress the "wave function" of a particle to distances shorter than that, you inevitably start to produce particle-antiparticle pairs and similar things. It's as far as you can get from the non-relativistic notion of an ordinary particle.

The particle is observed at a point not because the maximally compressed wave functions would be natural or "the best" or optimized in any sense - they're among the worst, most singular, most non-relativistic, most unlikely to be the right description. Particles are seen at points because the damn function has a probabilistic interpretation, it always has had, it always will have, and who tries to deny that this fact is established and demonstrable is complety confused about the basics of modern physics.

reader Luboš Motl said...

Dear Dilaton, it's true that "quantum mechanics" is often used for quantum laws where some natural variables only depend on time and not other continuous variables, i.e. for QFT in 0+1 dimensions, and I sometimes use this interpretation of "quantum mechanics" myself (e.g. "Matrix theory is a model of quantum mechanics").

However, in all these texts about the foundations of quantum mechanics, I use "quantum mechanics" in a much broader sense, as any theory respecting the general postulates of QM such as the linearity of the observables as operators acting on the Hilbert space, Born's rule, and so on. In this primary meaning of "quantum mechanics", any QFT in any dimension (and even string theory itself) is just a particular example of a quantum mechanical theory.

reader Luboš Motl said...

An excellent clarification, William, thank you!

The droplets just betray their being nothing else than a visualization of some features, not something that is supposed to be exactly equivalent to what it claims to model.

reader Luboš Motl said...

Excellent, William, and I had a similar experience except that the Hancock tower was in Boston, not Chicago, and it was a few days before 9/11 (and my thesis defense) when I visited it before the observatory got closer for years.

reader Luboš Motl said...

Jon, it often sounds that you are asking questions but you are never waiting for any answers.

There are answers to all your questions. We know that the "interaction that triggers the collapse" can't exist in the sense as a real process because such an interaction would have to act instantaneously, and it would therefore violate the laws of relativity.

You can phase the very same thing "experimentally", too. If such an interaction existed, it would have consequences that would manifest themselves as the violation of the Lorentz symmetry, and we observe there aren't any.

reader Holger said...

Lubos, I perfectly agree with most points you have raised - I only suggest to take them a little further. The concept of emergence does not need to stop at the point which we (currently) regard "fundamental". In fact, t'Hooft has demonstrated with a toy model how quantum mechanical features could emerge as well from something sub-quantum. In his example, that sub-quantum regime was classical, but there is no reason to restrict ourselves to classical models, why should we. Point is: In history, scientists often believed that they had reached the bottom, just to find out that the well reached far deeper. The question of "why does the neutron decay now" does certainly not imply a return to any classical concepts. We ask why because we want to know, and one day we may know why these processes look random in our labs.

reader Luboš Motl said...

Dear Holger, emergence (you mean the process of finding deeper explanations) doesn't have to stop at the point where science is now.

But it cannot get reverted. The fundamental theories people would have before the 20th century revolutions have been *falsified* so they can never be resuscitated.

Non-relativistic theories can emerge as the limit 1/c goes to zero of relativistic theories. But one just can never revert this arrow and derive relativity from a non-relativistic theory because the non-relativistic theories are more special - corresponding to a particular special value of the parameter 1/c, namely zero (corresponding to no Lorentz contraction, no speed limit etc.) - and once it's shown that Nature doesn't live in this special subset of theories, it can never be unshown.

The situation of quantum mechanics is exactly analogous. Classical physics is a special, hbar goes to zero, limit or special case of quantum mechanics. Just like relativistic effects (e.g. contribution to Lorentz contraction etc.) and corrections scale like positive powers of 1/c, quantum effects - like the uncertainty of variables and the unavoidable probabilistic interpretation following from that uncertainty - scale like positive powers of hbar. It's been shown that Nature doesn't live in the hbar=0 subset or limit of the space of possible theories. It follows that this special subset has been falsified and it cannot be unfalsified.

Your bigotry and obsession with undoing the quantum revolution is exactly analogous to the people who hope that the right explanation of Earth's shape will be a flat Earth again, or that creationism is right and the apparent evolution is just an illusion emerging from the Truth of Creation.

It just isn't so and can't be so, OK? All the "possibilities" you propose have been proven impossible. You may have overlooked this subtle fact - you may have overlooked the 20th century in physics - but it's still there.

reader Marcel van Velzen said...

“The question of "why does the neutron decay now" does certainly not imply a return to any classical concepts”
Yes it does. Don’t you even understand the Heisenberg uncertainty principle?

reader Leo Vuyk said...

Dear Lubos,
I appreciate and respect your blog very much, but imo. you are not honest by writing: “quantum mechanics doesn't need (and doesn't allow) any additional "interpretations". You either understand the theory or you don't.”
You also know that different interpretations of the symmetric universe (splitting locally or not splitting at large distances by CP symmetry ) could be possible.

reader Luboš Motl said...

Exactly, Martin.

Things may be converted to the usual x-p uncertainty principle but the more subtle time-energy version of the uncertainty principle may also be applied if we do it right.

If we measure the energy of the initial and final products with accuracy "delta E" or better (smaller), then the unavoidable uncertainty "dt" in the time of the decay does obey the usual

dt * dE is greater than hbar/2.

If we want to determine the point of the spacetime where it decayed as accurately as possible, we use the speed of the final particles, so the speed uncertainty can't be too high, and that implies an uncertainty of the position and therefore time of the decay, too.

reader Holger said...

OK, Marcel, then let me pass this "homework" to you: I have trapped my neutron inside a magnetic trap, within a volume of 1cm^3, at a temperature of 10^-3 Kelvin. How much does this trapping affect its lifetime?

You will find that the effects of Heisenberg's uncertainty can be conveniently neglected here. This was not my point anyway. I was asking about the why, and such a question necessarily perforates the framework of any currently known theory. Yet, I insist that science has to ask such questions in order to progress.

reader Jan said...

Ah well, the media. The actual researchers do not make any claims "this is the quantum mechanics" and alike, but rather point out some interesting similarities and promote further research. Putting the media campaign aside, the interesting mathematical description of this problem can be found here. arXiv:1401.4356v1 ... I would love to see your input on this paper, but it's kind of clear that you a) don't find it interesting at all b) your opinion may be biased before you even started reading the paper anyway, so I don't hold my hopes high. Actually the paper highlights some differences between QM and this experiment. On the contrary, various strictly quantum phenomena are being derived from the first principles, which is - in principle *putting shades on* - interesting. But the experiment itself is just an analogy or a visualization of some of the phenomena, nothing more. Even in the conclusion the authors claim that they consider this experiment to be useful as a teaching tool.

reader Marcel van Velzen said...

“Now, why did that particular neutron decay after, say, 10 minutes, while another sample decays after 15 minutes?”
You were talking about the width of the decay of the neutron (not effects of its environment), that’s Heisenberg. Wanting to know exactly when a particular neutron decays is by definition a return to classical concepts.

reader Marcel van Velzen said...

Pretty basic stuff isn’t it :-)

reader Holger said...

Nope, the width of the decay would be well covered by QM, it is a statistical notion. I was talking about the time at which a single, individual neutron is going to decay. I didn't touch any of those matters like precision here - give it an uncertainty if you like. A subquantum theory may have such an uncertainty, a jbar (as opposed to hbar). It may be quite different from hbar. It may possibly be zero as well (unless t'Hooft's deterministic example is mathematically flawed, which I am not aware of).

reader Guest said...

Qm is for those who don't want to understand nature.

reader Luboš Motl said...

Right, I give it the uncertainty I like - it's the very point of mine. The uncertainty may be arbitrarily large in general because of the superposition principle.

And no, Nature only contains one hbar. It's the conversion between quantities like energy to quantities like frequency (E=hf). The same relationship is pretty much equivalent to the Heisenberg or Schrodinger equations of motion or the path integral which govern *everything* in Nature. That's also why we can set hbar=1 - it is unavoidably a universal constant.

Everyone who tries to deny this thing is a crank regardless of the number of Nobel prizes he or she may have received for great work done 40 years ago.

reader Luboš Motl said...

I approved your comment to highlight my democratic credentials, and I have only placed you on the blacklist because I don't know the protocol to send you to a gas chamber.

reader Marcel van Velzen said...

So neutrons have different initial conditions and for that reason decay at different times? Is that what you’re saying? How are you going to know the initial conditions of the neutrons without interfering? Remember the double split experiment?

reader tomandersen said...

You said in post #1:

" waits until the “pilot wave” has damped"

It does not damp out.

No one thinks that there is anything but messy classical non linear physics going on in these experiments.

I think that you think its somehow cheating to have an energy source? The whole thing is lossy, as any experiment with waves on a fluid is. Its a puddle with drops, not QM.

reader Holger said...

Yes, different initial conditions. Surely nothing as simple as a "hidden classical variable" that has been forgotten to be implemented into the current framework of QM. It would have to be incorporated into another, more general theory which turns into QM in some of its limits. A very normal procedure, by the way. It would be very surprising if we were living in precisely that era in which all fundamental equations had just been laid out. But I have to point out that there exists no pressing need to extend the existing framework unless there exist obvious contradictions with experiments.

Just, it appears strange to me that current theories do not answer certain questions, instead yielding probabilities. It feels suspicious. And, no, it is no reason to find myself another universe. Just wondering what is going to come next, it may turn out to be more exciting than we think.

reader Marcel van Velzen said...

How are you going to know the initial conditions of the neutrons without interfering? Remember the double split experiment?

reader Holger said...

Obviously, such initial conditions do not show up within the framework of QM and hence do not affect the superposition of wavefunctions. Instead, they are most easily measured through the lifetime of the particle ;-)

reader Uncle Al said...

Every aspect of quantum mechanics requiring understanding can be resolved by inventing new families of virtual particles that cannot be made empirical to be detected. This tells you that approach is wrong.

If science is not better than that, abandon it. Seven billion people's lives intimately arise from the most eldritch of technological subtleties. Shut the valve. Two billion survivors can reevaluate their philosophical position.

reader Gene Day said...

Toward the end you almost got it right. The experiment is just a visualization, nothing more; it has no deeper significance. I can do the same with chalk and a blackboard.
I do not agree that the similarities are interesting. They are just a coincidence.

reader Gene Day said...

Lubos understands it. You do not.

reader jon said...

I don't understand the details, but in earlier posts you have said that inconsistent histories are eliminated when information arrives from separate locations, e.g. EPR. That seems to me to be enough to eliminate observing more than one particle in a dual slit experiment, without requiring faster than light processes. I apologize if it appears that I do not wait for your replies. I enjoy your blog quite a lot. I do admit that I am sometimes afraid of coming back to see harsh wording in your replies. If there is something wrong in my reasoning I would certainly like to correct it.

reader WolfInSheepskin said...

It's QM^{TM}

reader Curious George said...

Particle as a point .. take a 2 cm wavelength hydrogen superfine transition. At Goldstone I saw a high-pass radiotelescope filter for about that wavelength: a stainless steel(?) disc, 50 cm diameter, 2 cm thick, with a honeycomb pattern of holes. It reflects lower frequencies, lets higher frequency photons through. And still that photon can change a state of exactly one hydrogen atom.

To complement it, take a 10-m mirror of the largest telescope. A single photon of a visible light gets reflected from a whole surface; limit the diameter to 1 m and the resolution gets 10x worse.

reader Stephen Dedalus said...

First, I know personally the guys involved and they really know fluid dynamics. The experiment and the theory are really interesting and It's not only because of the similarities with QM (which I think are just similarities) , but because they are ingenious and creative. Also, the phenomena investigated are closely related with interfacial phenomena, coalescence, lubrication theory, faraday waves, hydrodynamical instabilities and other very relevant things (at least for the area) in nonlinear dynamics and chaos. The first experiments by Y. Couder didn't even mention the word "quantum".
I know its the way Lumos express his toughts and I particularly like it. However considering this series of experiment just a a bunch crackpot playing with droplets and trying to disprove one of the most succesful theory of physics isn't right.

reader Luboš Motl said...

Thanks for this voice.

Sex involving the transmission of sexually transmittable diseases also involves lubrication theory, droplet coalescence, when it's done in the shower, also hydrodynamic instabilities etc. etc. and the people participating in it may even know something about these things of classical physics and applied maths and think that they're quantum cool.

It doesn't imply that their act should be hyped as ingenious or a revolution in quantum physics. When QM is studied at some high or precise enough level, it simply has nothing to do with either of the two activities.

reader Leo Vuyk said...

Lubos knows that his “democratic
credentials”, should also contain a choice between level 1 to 4 of Max
Tegmark’s muliverses or as I believe a combination of a local and a distant NON
splitting mirror CP symmetric mulitverse, able to understand human and material

reader Gary Ehlenberger said...

Very, very, nice discussion on:

Quantum mechanics doesn't really imply solipsism
What do you think of

Bass's proof, only one consciousness assuming QM

reader Luboš Motl said...

I've read about 1/3 of the paper - not a compact clump, but representatively. I don't know what to do with it. It seems to parrot lots of misunderstandings by Einstein, add tons of sociological comments about the difference between philosophers and physicists, but ultimately fails to say what is right and fails to understand what quantum mechjanics - and Bohr - actually says about it, namely that the state vector is about the knowledge that is fundamentally subjective and there is therefore no contradiction at all if two observers use different state vectors.

reader kashyap vasavada said...

Thanks for pointing out Bass’ paper. This is an interesting work bordering on metaphysics and shows how Wigner’s friend paradox and singular nature of consciousness can be related. I do not know if Wigner himself believed until the end of his life that consciousness collapses wave function. It will be interesting to find out about this. For people like me, these are intriguing ideas which do not take anything out of the fantastic numerical success of QM. I can also see Luboš’ viewpoint that Copenhagen interpretation, mathematics of QM and super agreement with experiment are the only essential ideas.

reader Gary Ehlenberger said...

QBist metaphysics

reader Gary Ehlenberger said...

Check this paper out.