http://www.wired.com/2014/06/the-new-quantum-reality/
Have We Been Interpreting Quantum Mechanics Wrong This Whole Time?
265 thoughts on “Bohm Lives Again–(aka was Krishnamurti right? ;>} )”
Leave a Reply
You must be logged in to post a comment.
The Skeptical Zone
"I beseech you, in the bowels of Christ, think it possible that you may be mistaken."
I linkified the title of the wired article. I hope that’s okay with you.
Note: To do that yourself, click the icon that looks like a chain link (while editing). There will then be a space to add the url.
I’ve avoided interpretations of QM. I’m not convinced by any of them.
There is a good reason why Bohm’s pilot-wave theory has never caught on and probably never will. It is narrowly tailored to a single particle and cannot be extended to other systems.
In contrast, the good old Copenhagen theory allows one to obtain a quantum description of any physical system for which we can construct classical equations of motion. (On the technical level: equations of motion –> Lagrangian –> canonical pairs of coordinates and momenta –> quantization.)
In addition to the old Copenhagen QM, we have Feynman’s formulation of path integrals, which is again applicable to any physical system. This formulation is even better suited for the description of extended (rather than point-like) objects such as electromagnetic fields. For example, it incorporates relativistic invariance more naturally than the Copenhagen formulation. Quantum field theory, the cornerstone of modern particle physics, is expressed in Feynman’s language.
Bohmian pilot-wave theory is hopelessly behind the times. Even this article acknowledges that its supposed comeback is “minor” and is happening outside of the realm of quantum mechanics: “among fluid dynamicists.” These guys might find the analogy with pilot wave gratifying, but this in no way makes pilot wave useful in quantum physics.
Uh-oh: Here are some critical comments from Brian Leiter’s site:
Interpreting quantum reality: new evidence
Interesting piece sent along by reader Joe Hatfield–can any of the philosophers of physics (or physicists) out there comment on the adequacy of this presentation and the significance, if any, of all this?
FacebookTweetEmail
Posted by Brian Leiter on July 05, 2014 at 10:45 AM in Of Cultural Interest, Philosophy in the News, What is Philosophy? | Permalink
Comments
1
Tim Maudlin said…
The pilot wave theory is essentially as old as quantum theory itself (1927), and its complete adequacy in the non-Relativistic regime (i.e. its ability to generate the standard quantum-mechanical predictions without any conceptual problems or vague talk about “measurements” of “observables”) has been basically clear since Bohm’s 1952 paper. A deeper understanding of the origin of the statistical character of the predictions has been established by the work of Shelly Goldstein, Detlef Dürr and Nino Zanghì. There are various strategies for extending the theory to cover Relativistic field theory. All of this is known and appreciated by people working in foundations of physics, and particularly by most philosophers of physics.
These experiments provide a mechanical analog, to some extent, to the single-particle theory, and so can give people a sense of how the theory works. But the analog is very, very partial: it will not extend to entangled pairs of particles, and so cannot even vaguely replicate the most astonishing prediction of quantum theory, viz. the violations of Bell’s inequality. It also can be misleading about the structure of the quantum wave function. For a single particle, the wave function is a complex function over physical space, so the waves in the medium here can partially correspond to it. But when there is more than one particle the wave function is defined over the configuration space of the system, which is of greater than 3 dimensions, so this model fails.
Insofar as these experiments bring attention to the pilot wave theory (also known as deBroglie/Bohm theory and Bohmian mechanics), that is a good thing. But there is no conceptual breakthrough, and the model is misleading in some respects. John Bell strongly advocated the pilot wave theory for decades.
Reply July 05, 2014 at 04:16 PM
2
Curtis Franks said…
Independently of the question about the analogy between these behaviors of these oil bubbles and the Bohmian mechanics of single-particle systems (which do interest me a great deal), aren’t there nowadays concrete empirical reasons to think that Bohm’s theory is false?
If you have two measurables represented by hermetians whose commutators are non-zero (unlike what one finds in the simple two path experiments), and one of them is position, then facts about spectography predict that in basic set-ups where on the QM account a collection of pairwise entangled particles are each in a superposition of taking two trajectories and on the Bohmian account they each take one or the other trajectory according to statistical predictions, then the patterns of dispersion of the particles predicted by the two theories will differ. This has been known for a while, as it was analytically proved to be true many years ago. More recently (1999), specific experiments were described that would produce different outcomes on the two theories. Even though the experiments are variations of familiar double-slit experiments, there are subtle features that one has to get right. It was thought that the experiments would be too costly to actually conduct, and also that they would be too difficult to implement. But a few years ago one of these experiments was conducted and the results do not weigh in favor of Bohm’s theory. I believe this is the first paper about it:
http://arxiv.org/pdf/quant-ph/0206196v1.pdf
It is interesting that in their remarks in Wired, these mathematicians make no mention either of this or of the facts that Bell pointed out 60 years ago about the differences between QM and Bohmian mechanics with respect to Lorenze invariance.
I’m sure many of my colleagues who specialize in these topics can speak to the issues with more clarity and confidence, but I hereby register my amateur puzzlement.
Curtis
Reply July 05, 2014 at 10:40 PM
3
Tim Maudlin said…
The papers cited by Franks above , as far as I can tell, show nothing at all. For example, in the paper by Ghose there is a symmetry argument that would apply only to a set of measure zero in any case, and so cannot have any effect at on of the statistical predictions of the theory. Without going into details, the main paper also makes assertions (e.g. about ergodicity) that make no sense at all.
Other such supposed “proofs” that the pilot wave theory makes different predictions than standard quantum formalism have also been shown to be incorrect, typically because they fail to take account of the physical effects of the experimental set-up, i.e. they fail to appreciate that once one has solved the measurement problem by physical consideration, one can’t just ignore those physical considerations when extracting empirical predictions from the theory. So to reply to the puzzlement above: the papers there cited are in error.
Reply July 06, 2014 at 02:58 AM
4
Tim Maudlin said…
After a little more reading of the papers cited in the paper cited by Franks above: the work of Ghose is incompetent (see http://arxiv.org/abs/quant-ph/0007068), and the paper by Golshani and Akhavan also wrong at the critical point, where they claim to derive predictions for an unentangled wave function. (Golshani and Akhavan acknowledge that there are no differences in statistical predictions for “non-selective” measurements, and their claim for deviations elsewhere are incorrect.) Some of the papers cited seem not even to exist any more, i.e. have been deleted from the arXiv. There is really nothing in these claims.
I enjoyed this discussion at a layperson’s level of four approaches to interpreting QM from recent WSF:
QM Interpretations
I take such claims with a quantum of salt.
Glen Davidson
BruceS,
Wow, that looks really interesting. Thanks, Bruce!
This made me wonder what had happened to Feynman’s van.
A Nature essay on Quantum Bayesianism by David Mermin.
And here is Sean Carroll’s latest entry advocating Everett/Many-Worlds interpretation: Why the Many-Worlds Formulation of Quantum Mechanics Is Probably Correct.
(walto will probably appreciate this post as well: Physicists Should Stop Saying Silly Things about Philosophy.
Many-worlds my ar$e! (Disclaimer: I Am Not A Physicist). A new universe for every collapsed quantum wave, ever? Seems a tad extravagant on universes.
Sean Carroll’s article addresses this concern directly. I don’t believe it is considered to be an important objection to the MW interpretation at this time.
Instead there are two other concerns:
– the issue of how to understand the probabilities we see when we do experiments;
– the issue of preferred basis: roughly, why do we observe the standard quantities of physics, like position and velocity, and not some other outcome which could be possible by the formalism of QM.
Sean promises a followup post on these.
Thanks for all the interesting links, folks! (Sophisticat, FWIW, I agree with many of the comments made by the defender of philosophy in the Physicists Should Stop…. link. My own view is that the fields aren’t continuous (as Quine believed), and that (sensible) philosophical statements are of a sort that can’t conflict with empirical claims. Not because they’re “deeper” though.)
Again, thanks.
Allan,
I would say Sean Carroll (and Lawrence Krauss for sure) is exactly the reason why just because someone calls themselves a professor, we assume they know what they are talking about.
Exempli gratia:
Sean Carroll-
“Why, this objection goes, would you ever think of inventing a huge — perhaps infinite! — number of different universes, just to describe the simple act of quantum measurement? It might be puzzling, but it’s no reason to lose all anchor to reality.
To see why objections along these lines are wrong-headed, let’s first think about classical mechanics rather than quantum mechanics. And let’s start with one universe: some collection of particles and fields and what have you, in some particular arrangement in space. Classical mechanics describes such a universe as a point in phase space — the collection of all positions and velocities of each particle or field.
What if, for some perverse reason, we wanted to describe two copies of such a universe (perhaps with some tiny difference between them, like an awake cat rather than a sleeping one)? We would have to double the size of phase space — create a mathematical structure that is large enough to describe both universes at once. In classical mechanics, then, it’s quite a bit of work to accommodate extra universes, and you better have a good reason to justify putting in that work. (Inflationary cosmology seems to do it, by implicitly assuming that phase space is already infinitely big.)
That is not what happens in quantum mechanics. The capacity for describing multiple universes is automatically there. We don’t have to add anything.”
Horseshit in a can.
phoodoo,
After you’ve presented your probability calculations in the other thread, perhaps you can return here and explain exactly why you think Carroll is mistaken.
phoodoo,
In order to declare Carrol’s post “horseshit”, one needs to understand wha he is talking about. Do you know what phase space is, phoodoo? What role it plays in classical mechanics? And how are things different in quantum mechanics in that regard?
Go on, Mr. Rice Farmer, tell us like it is.
olegt,
I think that the fact that you believe the definition of phase space has the strength to make his argument formidable, shows how far off you are from understanding the validity of it.
His argument that multiple universes are likely is not only extremely un-parsimonious, its the antithesis of what people expect when they use the concept of scientific knowledge. Its as if one said, I believe in layers of chocolate cake, which exist just outside of our range of visual light. the reason why it is likely is because suppose you were to imagine they existed and then didn’t, one would have to wonder where the imagination came from. Its much easier to assume mathematically that its real.
His assertion is no more real then the assertion that a cat in a box is both alive and dead, until we look at it. NO IT FUCKING ISN’T, is the only appropriate reply to that.
Indeed, it’s far more logical that Jesus decides if the cat is alive/dead.
Hey, phoodoo, we’re not even discussing how strong Carroll’s argument is. I’m trying to see whether you even understand it. 🙂
What’s phase space, genius? What’s the difference between classical and quantum systems in connection with phase space? That’s what the argument is about. Say something that indicates you have a basic understanding of the question being discussed.
olegt,
Forgive me for not allowing you to decide what the questions are Mr.Trebek.
Translation: I have no idea what phase space is and I don’t understand Sean Carroll’s argument. I do know, however, that it is wrong.
🙂
olegt,
You have yet to prove you know what an argument is yet, so perhaps we better take baby steps.
Baby steps sounds fine. Let’s make sure both of us understand what the argument is.
Since the argument concerns phase space, let’s start with that.
I know what phase space is. (I teach statistical and quantum mechanics at undergraduate and graduate levels, where this concept is used.) Let’s see if you do. What’s the number of dimensions in the phase space of a particle (e.g., the electron) moving in our three-dimensional space?
olegt,
Unfortunately you don’t happen to know what a bad argument is, so your amazing ability to know what a phase space is (even before Carroll says exactly what is in in the quote, nonetheless!) is surprisingly useless.
Do you know what a chocolate cake in outer space is? Well, don’t worry, you don’t need to, because its equally irrelevant to the premise that multi-universes are likely with zero evidence for such a claim.
Without knowing what phase space is, phoodoo, you can’t understand what Sean Carroll is saying, and yet you have the temerity to say that his argument is “horseshit.” You are a know-nothing, my boy.
olegt,
Without knowing what an argument is, you can’t understand what horseshit is Olegt.
Do you know what an empty space is?
Do you know what an autohagiographer is?
How about we get back to some actual thoughtful discussion in this thread.
Neil Rickert,
That was my attempt Neil. One can not make arguments for multiple universes by referencing thought experiments.
But this is what science has come to in academia. Its the disease of the Michio Kakos, and Lawrence Krausses, and Richard Dawkin’s…
I heard Dawkins on a radio interview recently. He was asked about his peers thoughts on atheism. He said most of them are clearly atheists, but that they wouldn’t even feel the need to mention it, because the fact that there is no supernatural force is so obvious, its not even worth mentioning.
Its a patently stupid remark on the face of it, and even more so given that people consider him an educated commentator on the subject who should be listened to.
How one can conclude that its obvious that there is nothing outside of the materialist world we see is beyond understanding. If this is what the leading voices of an intellectual pursuit have to offer, why should anyone take the concept seriously? Its obvious? In what way exactly?
In the way that people just say bullshit because they are convinced they have fascinating insight by virtue of a clueless choir who are mesmerized by anything that sounds sophisticated ( he wrote a book, he knows!)
It makes it even better when said with a British accent apparently. Hell, If Sean Carroll was born in London multi-universes would almost be an indisputable fact.
phoodoo,
Allan,
It is a fair assumption, when they are talking of the subject in which they have a professorship. I don’t presume to be better placed to judge than Carroll, despite my light-hearted dismissal of Everett’s hypothesis. (Everett’s son is lead singer in Eels btw, a propos of nothing at all).
You people are quick enough to saddle up an expert when they appear to confirm your prejudices.
Toward the end of Sean Carroll’s post he writes:
That’s what phoodoo does. He doesn’t understand one percent of what Carroll is saying. But he still thinks Carroll is wrong.
Allan Miller,
Sean Carroll isn’t a professor, by the way. He is a senior research associate at Caltech.
Allan Miller,
You people?
Seems pretty straight forward to me and personally, I agree with that assessment. Where’s the problem?
The only way it can be “patently stupid” is if a) there’s a concise definition of “supernatural” and b) there’s a clear, unambiguous example of a supernatural force. Can you address both a and b then?
Ah, ah, ah, ah! No changing the subject Phoo. The issue is “supernatural force”, not “nothing outside the materialist world”. Can you provide evidence for the former? If not, the later is just a red herring.
It’s a legitimate point he raises. Thus far, all forces for actions in this universe appear to be accounted for in physics. So, in what sense would a “supernatural” force effect things in this universe? How would one go about detecting a “supernatural” force if all physical forces alone can be used to explain a given action? And given that, why posit supernatural forces at all. From a scientific perspective, such a concept adds nothing to our understanding of workings the universe and in fact are not indicated even indirectly.
Allan Miller,
Allan Miller,
Do you think you are better or even equally placed to be able to judge the premise that a cat in a box is both alive and dead at the same time, until it is observed to be so? Why would you renounce you ability to draw a conclusion about rationale thought to someone else, just because that person played with math? Do you have such little confidence in your ability to think?
Robin,
The supernatural force refers to the existence of a force outside of materialism. He wasn’t talking about its influence on the universe, simply on its existence. His statement is that it is obvious that nothing exists outside of the material world, thus his atheism.
Your logic continues to deteriorate when you state this:
The only way it can be “patently stupid” is if a) there’s a concise definition of “supernatural” and b) there’s a clear, unambiguous example of a supernatural force. Can you address both a and b then?
Why would there need to be an unambiguous example of a supernatural force, in order for it to be silly to conclude that it is obvious it doesn’t exist? You have jumped from asserting that it doesn’t exist to saying prove it does. A ridiculous jump of logic.
And then this whopper:
“Thus far, all forces for actions in this universe appear to be accounted for in physics.”
That is the equivalent of saying, there can’t be anything outside of the world we live in, because we can see all of the world we live in.
What is physics? Where does it come from? Why can we count on it? THIS is the biggest hole in the atheists playbook. They say, if life is controlled by a whole list of organized, predictable forces, then let’s just assume those are …..we don’t even have a word for it, they just are. Its as if the need to think stops right there. The world works, why should we believe it was supposed to work. It just does.
And in fact, the fact that it does work, is evidence AGAINST a creative force. THAT is the twisted logic of the atheist mind.
Once again, shitposts and responses to them dominate the “discussion.” Sad.
Starting with that question (which is the question asked by physics) derive any extant religion or system of theology.
How do you work your way from that question to any positive statement about the attributes of the deity of your choice?
petrushka,
I think the attributes of a deity, and ones believe in any such positive aspects is completely separate from acknowledging that if life works, and physics work, it is a piece of evidence FOR a purposely created construct, not evidence against one.
I would think would be obvious, …but not to the great mind of Dawkins and the like I guess. But he sells a lot of books, I guess that is all the evidence some people require.
And if it turns out that indeed, the quantum effect we have been counting on for the past 90 years really is just a result of a gap in our understanding, and thus we have been fooled (as this research is suggesting) , who are the ones who were the smart thinkers?
Those who said, “Well, I know it seems strange and illogical, but the experts say so, so….”
or are the smart ones those who said
“Hold on a second, you are making an extraordinary claim about the way the world works, and we are supposed to take your word for this, simply because you believe so? No, I will remain skeptical, perhaps we are simply missing part of the puzzle, the experts could be wrong. The cat is not both alive and dead”
It looks like it could well turn out that once again, the doubters beat the experts.
Don’t hold your breath, phoodoo. Quantum superposition has been demonstrated not just for electrons and other microscopic particles, but also for much larger objects, a fraction of a millimeter in size. First quantum effects seen in visible object.
phoodoo,
And if your aunt had bollocks she’d be your uncle, as we say in these parts. Yes, if things turn out one way, all the people who thought that’s the way things would turn out can peel themselves a victory banana. A curious thing, declaring provisional victory!
Schrodinger, incidentally, intended his cat to illustrate a problem for the Copenhagen interpretation. He didn’t think superimposed alive-dead states made any sense either, which is why he devised that illustration.
It is of interest in this case, as in all the semi macroscopic cases such as multi-slit interference experiments with C60 buckyballs that one can describe the preparation in terms of a superposition of states, but one never finds a superposition of facts (actual events or states of affairs). Not surprising when we recall with Bohr: “any attempt to more closely follow the course of events requires a change in the experimental apparatus incompatible with the manifestation of the original phenomena”.
This leads me to surmise that the only thing that ever get superposed or entangled in quantum physics are counterfactuals. This is of course also a denial of the eigenvalue eigenstate link and is tantamount to a repudiation of the EPR criterion of “reality”.
empaist,
I wonder why Olegt hasn’t responded to this?
Is that all it takes to make the boy wonder silent?
What about all the stuff you’ve avoided?
Mote/beam/eye.
OMagain,
I think the more serious discussions, by their very nature, don’t involve evolutionist preachers because there is no actual substance there to argue over in any case.
Their bananas are stale.
Indeed, hence the dearth of academic publications by said preachers.
At least they exist to be argued over. How much larger then 0 is 1?
I am not sure there was anything to respond to.
Well, there is something we both agree on. There is indeed a dearth of academic publications from evolutionists which describe the exact steps or mechanisms in evolution. In fact, perhaps the only quibble is the use of the word dearth, as opposed to “complete absence” of such publications which is far more accurate language. Its as if they came up with a theory, without a description. Life perhaps evolves, somehow, in some way, by some unknown forces. I guess its pretty tough to get an article published that only says this, so they don’t bother.
In this case, the better question is, how much larger is 0 than 0?