I really do hope that we can find a way to make sense of everything in Physics, but Bohm's description of the infinite in the article is rather fascinating. Maybe there's no way out after all
The (completely classical) fluids "experiment on television" mentioned in this article is presumably something like this (which is really cool if you haven't seen it before):
IMHO the Copenhagen interpretation should have been taken as "this is the best we can come up right now" (instead of an "all-in") and while the original Bohmian mechanics do have some issues it does sound like they threw the baby out with the bathwater.
(In the end the most successfully interpretation has been the "shut up and do the math" one, but the interpretations help us find unexplored and contradictory sides of the theory and hopefully help to find new experimental possibilities)
Maybe the bad idea is insisting in having a classical physics pictorical interpretation when there's no reason why there should be one. At some point having just Maths is the more reasonable outlook.
> Maybe the bad idea is insisting in having a classical physics pictorical interpretation when there's no reason why there should be one
Actually there is a reason: we see classic physics with our own two eyes every day. We know classical physics exists at the macroscopic level, and so a theory that simply explains the transition from microscopic to macroscopic physics and how this works.
This transition is unbelievably simple in Bohmian mechanics, since in principle, it's just classical physics with an extra term to account for quantum influences. The picture isn't nearly so simple for many other interpretations.
We think we see classical physics, but this micro/macro divide is not that clear-cut. It's more like a convenient textbook classification. For instance you can build a very macro magnet which is not classical physics at all, you can't explain ferromagnetism without QM. Why don't we fall through the floor? that's not classical. Chemistry makes no sense without QM either. A classical world, albeit nice and easy to mirror with mental images involving differential equations of continuous stuff would fall to pieces.
I like Bohm's book on Quantum Physics, but the pilot wave theory... well it doesn't explain anything new and the only problems it might solve are related to prejudices. Besides, the nature of that duplicity is never explained (and very ugly), so you're trading the ignorance you don't like for the one you like. In this kind of situations just go for the more simple and consistent theory as the only thing that matters is measurements.
(There's also the problem of getting to some form of QFT with it. Bell has written about this elsewhere, it's not pretty but I'm sure somebody has arrived to a working model by now.)
You're statements attempt to negate the GP's claim that the macro is classical by saying that the micro is not classical. But that's the whole larger question we're trying to answer here, so asserting an answer in one direction (micro is not classical) as a reply to some sub-point ends the possibility of a reasonable discussion.
If there is a formulation of quantum mechanics which retains classical determinism, then just because it coheres so well with the behavior of everything we have directly observed (insofar as that's possible through the intermediaries of our senses) so far, it should be given a good amount of attention.
> but the pilot wave theory... well it doesn't explain anything new and the only problems it might solve are related to prejudices.
It can only be considered a prejudice if you're already pre-decided that non-classical physical descriptions are necessary before attempting to evaluate pilot wave theory. You're saying the prejudice is against non-classical behavior, right? Just put yourself in the shoes for a moment of a person judging (the modern formulations of) these theories, but at a point in time before any of them had a reputation (in an alternate history I mean). Would it be a prejudice to select from among essentially equivalent (predictive power) theories the one which doesn't force us to leave the then reigning classical paradigm?
If Pilot Wave theory and the more established quantum theories have comparable predictive power, but pilot wave theory can do the same thing without introducing new classes of behavior never observed at the macro level, then that's a point in its favor via Occam's Razor if nothing else.
No, I'm actually saying that everything is QM, and yet for some phenomena you can use instead of that some effective theories called classical physics, that have these nice properties of needing just calculus and vector analysis and being easy to draw. That, and they having been discovered before more explanatory theories make them very popular, but it doesn't mean the world is actually separated in domains. Usually physics is taught in terms of micro and macro descriptions, the macro applies to those situations likely to be adequately characterized by classical physics, but that's because Planck's constant is really small, not because there's such a thing as a classical world. Hence for macroscopical everyday stuff classical physics usually works reasonably well, but even there, right in front of you there are very obvious phenomena that can't be explained with classical physics.
About the pilot wave theory, well it came after the standard formulation of QM, so people didn't choose between them, and it's quite a patchwork that brings its own complications. Apparently as it includes classical trajectories some people love it, ignoring that you put by hand the actual QM wavefunction to make it work, then you fix things to get the old stuff back. I find all that weirder than standard QM.
I assumed that's what you're saying. I'm familiar with the viewpoint that classical physics is a pragmatic approximation to QM for macro phenomena.
> About the pilot wave theory, well it came after the standard formulation of QM, so people didn't choose between them
Of course. I was posing a hypothetical to demonstrate an error the argument you were making (assuming the conclusion as part of your argument).
> ignoring that you put by hand the actual QM wavefunction to make it work, then you fix things to get the old stuff back. I find all that weirder than standard QM.
I may be missing something here, and I haven't looked into the calculational details of pilot wave theory, but my understanding is that the same probabilities you ordinarily deal with in QM exist, but they are used to signify lack of knowledge of the observer of the state of the system (rather than saying that the system is literally in an indefinite state), so it makes sense that the wavefunction machinery would still be present, but used in a different way.
I think you might be using an overly simplistic meaning for "classical". There is nothing preventing a classical description of ferromagnetism, for instance [1]. Bohmian simulations of atoms has established stability despite the orbits, and would similarly entail the diamagnetism needed for this phenomenon, so classical theories can in fact explain it.
> well it doesn't explain anything new and the only problems it might solve are related to prejudices.
Correct, it actually explains everything old which prior interpretations like Copenhagen could not. I assume by "prejudices", you're referring to classical prejudices, but I think those prejudices are perfectly warranted.
> In this kind of situations just go for the more simple and consistent theory as the only thing that matters is measurements.
I disagree! John Bell formed the first no-go theorem because he was a fan of Bohmian mechanics. Without this focus on interpretations and quantum fundamentals, we may never have seen that landmark result or the series of subsequent no-go theorems which have all proven critical to our scientific understanding.
Science and physics does not consist solely of measurements; considerations of ontology are at least equally important because they inform the thought experiments which really drive scientific revolutions.
> Bell has written about this elsewhere, it's not pretty but I'm sure somebody has arrived to a working model by now
There are a few workable models, but Bell was correct to say that non-locality was the unsolved problem of quantum mechanics. Other interpretations let you "solve" it by sweeping it under the rug, but it always rears its ugly head elsewhere.
No, they can't explain ferromagnetism. Sometimes you use a semiclassical approximation, but that's a technical term. Don't look into the words used in Physics, this is not a social science, words in themselves don't carry an inherent meaning, they're just labels. You need spin to describe ferromagnetism, there's no room for that in a classical model of charges.
I'm not opposed to alternative formulations of QM, but I'd rather prefer people would try to come up with more fundamental theories than QM (if possible) instead of trying to get the same results with something else because for some ideological reason they don't like standard QM.
And it really is all about the measurements: Physics is an experimental science. You can think all you want and do crazy math and lots of gedanken, but we need at least a number and see what Nature thinks about it.
Did you even read the link I provided? I mean, you've basically said that the physics textbooks are wrong and used a bunch of words, which you yourself said I shouldn't trust, to dismiss them without evidence.
> You need spin to describe ferromagnetism, there's no room for that in a classical model of charges.
I suggest you actually read the link I provided. A classical theory has certain characteristics that distinguish it from something like a quantum theory. As I suspected in my initial reply to you, you have a bizarre notion of what constitutes a classical theory. Rest assured, a classical theory of spin and ferromagnetism is entirely possible.
As for measurements, physics is not solely an experimental science. Yes, theory must match experiment because empirical knowledge is what we're after, but measurements alone do not advance this agenda.
Yes, I've checked it and understood what it said. If you take spin, which can't exist by itself in classical physics and use it in a semiclassical approximation you get a good enough approach for your problem that has workable maths. People do this all the time in quantum optics, you consider for instance quantum atoms and classical EM fields, because the whole machinery would be too much trouble. But that's not classical at all, it's just model building. With classical physics alone you wouldn't be able to calculate anything because it wouldn't provide the basic phenomenology. Try to build a classical theory of the photoelectric effect, it's impossible yet it opens the door of your elevator.
> If you take spin, which can't exist by itself in classical physics
There are literally dozens of papers you can readily find that reproduce spin predictions using classical statistical mechanics. You denounce this as "model building", but every physical theory was model building.
> Try to build a classical theory of the photoelectric effect, it's impossible yet it opens the door of your elevator.
No, a Texas section APS meeting presentation about some fun academic exercise is simply some fun academic exercise for a Texas section APS meeting. If you're not familiar with these things, well this is a profession, it takes more than googling stuff.
This is exactly what I was talking about, you consider that your atom has energy levels and then you plug in classical EM fields, sometimes that's good enough to get somewhere. But it can never be classical because there's no way to have energy levels in a classical atom.
Just take one positive charge and one negative charge (let's call electron to this one), then use Maxwell equations (you need the Liénard–Wiechert potentials) and try to calculate the energy of the electron, now it has a trajectory and everything. It's not for the faint-hearted (you have to learn classical electrodynamics first -whose consistency problem BTW has only been solved recently, or at least that's what Rohrlich thinks about it-). You won't get discrete energy levels, you won't even get a stable atom. Precisely this was the starting point of QM: Bohr coming up with a quantization rule for angular momentum and magical orbits where the accelerated classical electron does not radiate. Check "old quantum theory".
These problems were solved almost a century ago, the thing is people don't study enough or apparently have forgotten about them. They simply consider the QM postulates and then wonder why all that happened. Well, don't start the house by the roof, study what you should know already, the answers are there.
> This is exactly what I was talking about, you consider that your atom has energy levels and then you plug in classical EM fields, sometimes that's good enough to get somewhere. But it can never be classical because there's no way to have energy levels in a classical atom.
And this is what I'm talking about: this conversation is becoming an ever-shrinking pocket of you claiming, "well that's not classical", or "that can't be done in a classical theory", and me demonstrating that it has been done, toy theory or not.
I have no problem with discrete theories, I have a problem with people claiming something can't be done when it most assuredly can.
As for your derivation of old QM, I don't see how this is relevant. You seem stuck in the mindset that "classical theory" means building off of some known classical theory. As I've been saying, this isn't necessarily true. My discussion of classical theories are about the class of theories with various properties that differentiate it from something like QM.
People working on Bohmian mechanics are perfectly familiar with the history of quantum mechanics, see [1]. This doesn't somehow negate the fact that Bohmian mechanics can be viewed as a classical theory that nevertheless reproduces the predictions of QM. And it solves the radiating electron orbit problem just fine. Again, you're stuck thinking about this like classical mechanics rather than as a different classical theory that reduces to classical mechanics in the limit.
Let's assume the Maths is all we care about. One way to clear it up is to decide what we would need to give to a computer to figure out the results. Let's assume the computer can solve any equation we give it.
Bohmian Mechanics: Given Schrödinger's equation, Bohm's equation, the initial positions of the experiment and the measuring apparatus (assuming it is set on autopilot) and the initial wavefunction of the joint experiment and apparatus setup, then we evolve the system and the positions of the stuff in the apparatus will tell us the result of the experiment. Done.
Copenhagen Interpretation: We need Schrödinger's equation for the experimental setup, the initial wavefunction of the experiment, and some explicit timing for collapse as well as some stand-in for the eigenstates (we never actually collapse to an eigenstate or anything spiky, but rather to a nearby smooth state, such as a finite sum of Gaussians). We can optionally add-in the apparatus or observer wavefunction and collapse to something with an outcome involving those wavefunctions. It is kind of a mess to tell a computer how to do this, particularly if you have a number of experiments, possibly conditioned on the results of other experiments. It is not an independent time evolution. The Maths fail us in setting up a universe.
One could let this multi-experiment setup evolve until everything is done and then collapse at the very end. That leads to less of a mess of specification, but now one has the fact that we are saying reality does not have, in any, even approximate, sense, a definitive experience such as the one we are used to, at any point except for the last one. In some sense, this is the Many Worlds theory.
GRW is based on the idea of adding automatic collapse into the equations and that's fine and cool; it hits the wavefunction with a gaussian every so often. One also has to add in something else of an ontological nature, but that can be considered a philosophical issue (though it can matter what one chooses, say from a relativistic point of view). We at least have in GRW a Maths based evolution though it is different than the standard one.
The Copenhagen Interpretation is not an actual theory; there is no possible universe where it could be true or implemented. It can be made more specific, but it does require something more and the more one sticks to the Copenhagen spirit, the more of a "on high" specification mess, it becomes.
Both GRW and Bohmian Mechanics at least could be true.
All of it: that's the actual understanding of the world, right there. What else should it be? I don't expect the laws of Nature being intuitive for advanced mammalian brains ultimately.
Kip Thorne here [1] agrees with one aspect of Bohm’s philosophy (not Physics) —- he posits that theories that explain nature’s laws with more and more precision are like Matryoshka Dolls (Greeks->Newton->Einstein->String Theory->{??}), where each new layer improves on the predictions of the previous one —- and at one point in the discussion, he says this could go on until infinity.
(Regardless, this is a great interview to watch if you are interested in physics)
In similar vein, here is Eric Weinstein [2] talking about why we can’t find the theory of everything — and has similarly...kooky...ideas as Bohm. He is short-String theory (https://www.edge.org/response-detail/25547). His main critique comes from the demands that the theory starts imposing about wanting 11 or 26 dimensions.
All this in some level is super exciting and suspenseful, as I do believe Physics is on the cusp of a “new big idea from a lone genius” type revolution, that might push things forward!
Maybe something to do with him hanging out with Jiddu Krisnamurthi for decades ( before falling out). Joking aside, I did enjoy the conversations between the two that some kind soul uploaded to youtube couple of yrs ago.
My apologies for the seemingly unrelated comment, but I do not understand why 'spooky action at a distance' has to be 'action at a distance' and not photons getting entangled when created.
I.e. why couldn't it be that a pair of photons are generated with their properties already in such state that, when measured, a correlation is present? the photons don't communicate, they are already in the appropriate state when measured.
That is what Bell's work showed is not possible. The inequality he derived assumes the values already exist and then proves that a certain inequality for the predictions must be satisfied. This is without specifying the actual theory, just simply that the values already exist in the right correlations. Experiments has proven that the inequality is violated. Thus, the properties cannot be determined beforehand. So either there is a connection that is, essentially, faster than light, or the results of the experiments do not become finalized until compared (that is, the researchers first reading the results exist in a multi-state, allowing for various outcomes yet to be determined [this is what the many worlds view basically is] ).
Various no-go theorems were formulated due to looking into this question. For instance, the very first no-go theorem, Bell's theorem, was published because Bell was such a big fan of Bohmian mechanics.
>For him, truth-seeking was not a game, it was a dreadful, impossible, necessary task. Bohm was desperate to know, to discover the secret of everything, but he knew it wasn’t attainable, not for any mortal being. No one gets out of the fish tank alive.
This is a very, very big question. Its a little pity he didn't meet Sadhguru.
"not a game" - well, he certainly hid this well behind a playful and enthusiastic way of teaching, as when he was our Props of Matter lecturing prof at Birkbeck College in the early 70's. And very effective too, not that I followed the Physics path beyond that (the siren call of computers was stronger for me).
I didn't read the article but, in case you don't know quantum mechanics, I should tell you that the vast majority of people who study such things think that Bohm's theory is plain wrong.
I should also say that it is not taught in schools, papers about it are not published in serious journals and the field is just not an active field of research. It's quite likely that all the people trying to develop this idea are crackpots.
I really do hope that we can find a way to make sense of everything in Physics, but Bohm's description of the infinite in the article is rather fascinating. Maybe there's no way out after all