How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics
Many people here know that I am a “Bohmian”, i.e. an adherent of a very non-orthodox interpretation of quantum mechanics (QM). Indeed, in the past, I have published a lot of papers on Bohmian mechanics in peer-reviewed journals from 2004 to 2012. So how can I not worry and love orthodox QM? As a “Bohmian”, shouldn’t I be strictly against orthodox QM?
No. If by orthodox QM, one means instrumental QM (which is well explained in the book “Quantum Theory: Concepts and Methods” by A. Peres), then orthodox QM is fully compatible with Bohmian QM. I am not saying that they are equivalent; indeed Bohmian QM offers answers to some questions on which instrumental QM has nothing to say. But I am saying that they are compatible, in the sense that no claim of instrumental QM contradicts any claim of Bohmian QM.
But still, if instrumental QM has nothing to say about certain questions, then why am I not worried? As a “Bohmian”, I certainly do not consider those questions irrelevant. So how can I not worry about it when it says nothing about questions that I find relevant?
The answer is that I stopped worrying and learned to love orthodox QM precisely because I know about Bohmian QM. But let me explain it from the beginning.
I always wanted to study the most fundamental aspects of physics. Consequently, as a student of physics, I was much more fascinated by topics such as particle physics and general relativity than by topics such as condensed matter physics. Therefore, my graduate study in physics and my Ph.D. were in high-energy physics. Nevertheless, all the knowledge about quantum field theory (QFT) that I acquired as a high-energy physicist did not help me much to resolve one deep puzzle that bothered me about QM. The thing that bothered me was how could Nature work like that. How could that possibly be? What could be a possible physical mechanism behind the abstract rules of QM? Should one conclude that there is no mechanism at all and that standard QM (including QFT) is the end of the story?
But then I learned about Bohmian QM, and that was a true revelation. It finally told me a possible story of how could that be. It didn’t tell how it is (there is no direct evidence that Bohmian mechanics is how Nature works), but it did tell how it might be. It is comforting to know that behind the abstract and seemingly paradoxical formalism of QM may lie a simple intuitive mechanism as provided by Bohmian QM. Even if this mechanism is not exactly how Nature works, the simple fact that such a mechanism is possible is sufficient to stop worrying and start to love instrumental QM as a useful tool that somehow emerges from a more fundamental mechanism, even if all the details of this mechanism are not (yet) known.
However, something important was still missing. Bohmian QM looks nice and simple for non-relativistic QM, but how about relativistic QFT? In principle, Bohmian ideas of that time worked also for relativistic QFT, but they did not look so nice and simple. My question was, can Bohmian ideas be modified such that it looks nice, simple, and natural even for relativistic QFT? That question motivated my professional research on Bohmian QM and I published a lot of papers on that.
Nevertheless, I was not completely satisfied with my results. Even though I made several interesting modifications to Bohmian QM to incorporate relativistic QFT, neither of those modifications looked sufficiently simple and natural. Moreover, in arXiv:1309.0400, the last specialized paper on Bohmian mechanics I wrote, a referee found a deep conceptual error that I was not able to fix. After that, I was no longer trying to modify Bohmian QM in that way.
Nevertheless, partial satisfaction came from a slightly different angle. In an attempt to make sense of the local non-reality interpretation of QM, I developed a theory of solipsistic hidden variables which is a sort of a hybrid between Bohmian and Copenhagen QM. In this theory, an observer does play an important role, in the sense that Bohmian-like trajectories exist only for degrees of freedom of the observer and not for the observed objects. That theory helped me to learn that, to understand why we observe what we observe, it is not necessary to know what exactly happens with observed objects. Instead, as solipsistic hidden variables demonstrate, in principle it can be understood even if the observed objects don’t exist! It was a big conceptual revelation for me that shaped my further thinking about the subject.
But it does not mean that I became a solipsist. I don’t believe that observed objects don’t exist. The important message is not that observed objects might not exist. The important message is that the exact nature of their existence is not so important to explain their observation. That idea helped me a lot to stop worrying and learn to love orthodox QM.
But that was not the end. As I said, in my younger days, my way of thinking was largely shaped by high-energy physics and not by condensed matter physics. I thought that condensed-matter physics cannot teach me much about the most fundamental problems in physics. But it started to change in 2010, when, by accident, I saw in Feynman’s Lectures on Physics that Bohmian mechanics is related to superconductivity (see here) That suddenly made me interested in superconductivity. But superconductivity cannot be understood without understanding other more basic aspects of condensed-matter physics, so gradually I became interested in condensed-matter physics as a field. One very interesting thing about condensed-matter physics is that it uses QFT formalism which is almost identical to QFT formalism in high-energy physics, but the underlying philosophy of QFT is very different. Condensed-matter physics taught me to think about QFT in a different way than I was used to as a high-energy physicist.
One of the main conceptual differences between the two schools of thought on QFT is the interpretation of particle-like excitations resulting from canonical quantization of fields. In high-energy physics, such excitations are typically interpreted as elementary particles. In condensed-matter physics, they are usually interpreted as quasiparticles, such as phonons. Since I was also a Bohmian, that led me to a natural question: Does it make sense to introduce a Bohmian trajectory of a phonon? An obvious (but somewhat superficial) answer is that it doesn’t make sense because only true particles, and not quasiparticles, are supposed to have Bohmian trajectories. But what is a “true” particle? What exactly does it mean that a photon is a “true” particle and a phonon isn’t?
It was this last question that led me to my last fundamental insight about Bohmian mechanics. As I explained in Sec. 4.3 of arXiv:1703.08341 (accepted for publication in Int. J. Quantum Inf.), the analogy with condensed-matter quasiparticles such as phonons suggests a very natural resolution of the problem of Bohmian interpretation of relativistic QFT. According to this resolution, the so-called “elementary” particles such as photons and electrons described by relativistic QFT are not elementary at all. Instead, they are merely quasiparticles, just as phonons. Consequently, those relativistic particles do not have Bohmian trajectories at all. What does have Bohmian trajectories are some more fundamental particles described by non-relativistic QM. Non-relativistic QM (together with Bohmian interpretation) is fundamental, while relativistic QFT is emergent. In this way, the problem of the Bohmian interpretation of relativistic QFT is circumvented in a very elegant way.
There is only one “little” problem with that idea. There is no experimental evidence that such more fundamental non-relativistic particles exist in Nature. Perhaps they will be discovered one day in the future, but at the moment it is only a theory. It is not even a proper theory, because it cannot tell anything more specific about the exact nature of those hypothetical non-relativistic particles.
Nevertheless, there are at least two good things about that. First, unlike most other versions of Bohmian mechanics, this version makes a testable prediction. It predicts that, at very small distances not yet accessible to experimental technology, Nature is made of non-relativistic particles. Second, at distances visible by current experimental technology, this version of Bohmian QM says that Bohmian trajectories are irrelevant. This means that, as far as relativistic QFT is concerned, I do not need to worry about Bohmian trajectories and can love orthodox QFT, without rejecting “common sense” in the form of non-relativistic Bohmian mechanics on some more fundamental scale. That’s how I finally stopped worrying and learned to love orthodox QM.
Theoretical physicist from Croatia
But who says that the clicks are more real than the particles and fields.The minimalist interpretation of quantum mechanics seems to do that.
Instead of talking about objective and subjective, perhaps it would be better to talk about ontic and epistemic. The meaning of the latter words is well understood in philosophy. The only problem is that scientists are often not familiar with philosophic terminology.
Anyway, I believe that your quantum philosophy could be summarized and translated to philosophical language by stating that detector clicks are ontic, while all mathematical objects in quantum theory are epistemic.Hi, firstly, ontic and epistemic are not stuff of philosophy.. even brilliant physicists like Sean Carrol believes in ontic psi as when he made clear in:
http://blogs.discovermagazine.com/c…hysicality-of-the-quantum-state/#.Wa87v7pFxOx
“According to instrumentalism, palaeontologists talk about dinosaurs so they can understand fossils, astrophysicists talk about stars so they can understand photoplates, virologists talk about viruses so they can understand NMR instruments, and particle physicists talk about the Higgs Boson so they can understand the LHC. In each case, it’s quite clear that instrumentalism is the wrong way around. Science is not “about” experiments; science is about the world, and experiments are part of its toolkit.”
Also remember PBR theorem revolves around ontic and epistemic psi, so these are serious physics stuff.
That said. If psi is really ontic, and there is some kind of actual Hilbert Space in the vacuum or whatever the ontic nature may be based on.. is there possibility that we have new force of nature (or new field such as higgs field like thing) that only work in the dynamics within the actual Hilbert space (or other mechanisms) that produces the ontic psi, etc.? Do you know of references with regards to this? Thank you.
– who on earth makes detectors out of particles and fields?Everybody only uses particles and fields, because everything is described by particles and fields, and you need the known natural laws to construct apparati to make observations and experiments.
It doesn't matter whether you call something "subjective" or "epistemological". Just spend a sentence or two saying what you mean by either one.I did several times in this thread. Then you use the words in different meanings. In this way one cannot discuss scientific issues. That's all I'm saying.
That's what makes no sense to me. If detector clicks are natural phenomena that are ultimately described by the physics of particles and fields, then how can they be more real than what they're made out of? To me, that's a schizophrenic point of view.But who says that the clicks are more real than the particles and fields.
… detector clicks are natural phenomena that are ultimately described by the physics of particles and fields, then how can they be more real than what they're made out of? …- who on earth makes detectors out of particles and fields?
Anyway, I believe that your quantum philosophy could be summarized and translated to philosophical language by stating that detector clicks are ontic, while all mathematical objects in quantum theory are epistemic.That's what makes no sense to me. If detector clicks are natural phenomena that are ultimately described by the physics of particles and fields, then how can they be more real than what they're made out of? To me, that's a schizophrenic point of view.
The pre-quantum theories of physics were not schizophrenic in this way. Bohmian mechanics is not schizophrenic in this way.
I give up. One cannot discuss if there's no standard use of words :-(.That's just not true. You can ask people what they mean, and then go from there. If even after explaining, you're still not clear, you can ask for more clarification.
It doesn't matter whether you call something "subjective" or "epistemological". Just spend a sentence or two saying what you mean by either one.
I actually don't think that "epistemological" is the right word. Because to me that implies that there is some set of facts to know, and your theory describes your knowledge of those facts. In operationalist QM, there is no specification of what the facts are independently of what we know about them.
Perhaps it's something like quantum physicists who forget functional analysis when suits them. (I should know, I do this often.)Or maybe what I do – forget QM when it suits me and get hung up on functional analysis eg my sojourn in Rigged Hilbert Spaces.
Bottom line is respectful dialogue is pretty much always the way to go and sometimes those (including me) with strong views can forget it.
We all have to work at it.
Thanks
Bill
I thought philosophers were trained in logic – but for some reason certain ones forget it when suits them.Perhaps it's something like quantum physicists who forget functional analysis when suits them. (I should know, I do this often.)
“To ridicule philosophy is really to philosophize.”lTo critically examine something is that ridicule or intellectual debate. It was often said of Feynman, who was well known anti philosophy, that such a view is itself a philosophy. Logical recursion – yes – true – yes – but I think people understood what Feynman was saying without getting confounded by things that are true, but miss the point. That's the difference between some philosophical reasoning and what people do in everyday discussion. Maybe if it was more like everyday discussion philosophers would get further – that pretty much is what science has done.
Tthanks
Bill
“To ridicule philosophy is really to philosophize.”
― Blaise Pascal
I recently learned why there is no much progress in philosophy. Because when there is, it is no longer called philosophy.
http://consc.net/papers/progress.pdfNice.
Personally I think a lack of what I call a real devotion to clear thinking is a big part of it.
I am listening to a panel discussion program at the moment called Q&A. They are having a discussion panel of stated leftest philosophers. Now I am not a leftest – its a legit position, but just not mine, but the illogical statements being made – its – well confounding.
They were talking about the confrontation of the white fascists and the anti-white fascists that recently took place in the US. One said its impossible to not take a side in this. Really – I personally don't like either – violence even against vile tripe like neo-nazi white supremacy is not the way of a free society. We have free speech – and should use it. I think both are wrong. Yet they make – well badly reasoned statements like that as if it's axiomatic. It isn't. I thought philosophers were trained in logic – but for some reason certain ones forget it when suits them.
Thanks
Bill
I think the more philosophical we get the more uncertain our notions get and the more fruitless is the outcome.I recently learned why there is no much progress in philosophy. Because when there is, it is no longer called philosophy.
http://consc.net/papers/progress.pdf
Yes, and it's a difference between objective vs. subjective and ontic vs. epistemic. I tried to argue about this some postings ago, but to no avail. I think the more philosophical we get the more uncertain our notions get and the more fruitless is the outcome.
I think it's right that all the QT formalism is epistemic, and what's ontic are the outcomes of measurements, i.e., the irreversibly stored data of macroscopic devices.
I give up. One cannot discuss if there's no standard use of words :-(.Instead of talking about objective and subjective, perhaps it would be better to talk about ontic and epistemic. The meaning of the latter words is well understood in philosophy. The only problem is that scientists are often not familiar with philosophic terminology.
Anyway, I believe that your quantum philosophy could be summarized and translated to philosophical language by stating that detector clicks are ontic, while all mathematical objects in quantum theory are epistemic.
I give up. One cannot discuss if there's no standard use of words :-(.
This is a very strange definition of objective vs. subjective.The two words come from the words "subject" and "object".
Usually one means something is objective that it's independent of the observer performing the experiment. In this sense the only "subject" of scientific research are "objective" properties of nature. In my example of the Stern-Gerlach experiment there's a well-defined objective procedure to provide particles with a well-determined spin-##z## component (when the magnetic field is directed in ##z## direction).But the procedure is not about electrons, it's about experimenters. So it's subjective.
I guess if you're studying physicists, then it's objective, but if you're the physicist studying electrons, then it's subjective.
This is a very strange definition of objective vs. subjective. Usually one means something is objective that it's independent of the observer performing the experiment. In this sense the only "subject" of scientific research are "objective" properties of nature. In my example of the Stern-Gerlach experiment there's a well-defined objective procedure to provide particles with a well-determined spin-##z## component (when the magnetic field is directed in ##z## direction).
Then define, what you mean by objective vs. subjective.If somebody is studying something, the entity doing the studying is the subject and the thing being studied is the object. If a theory is about the object, then it's objective, and if it's about what the subject knows, then it's subjective.
The description of QM in terms of preparation procedures and measurement results is a subjective theory. Bohmian mechanics, on the other hand, is objective.
Well, Vanhees says that the quantum state is objective because it is an equivalence class of preparation procedures. That's what I would call subjectve. It seems the same to me as the idea that the quantum state represents our information about the system, which is a subjective notion of the state.Then define, what you mean by objective vs. subjective. A given preparation procedure (e.g., a Stern-Gerlach apparatus with well defined magnetic field and particles run through it) is objective, any physicist at any time at any place will get the same state when running the particles through this well-defined apparatus. If that wouldn't be the case, physics as we know it would be obsolete, all our technical devices we all use all day wouldn't work anymore as expected etc. etc. Fortunately this is not what we observe ;-).
I'm not sure what you mean. In quantum mechanics, the hamiltonian (including the potential) is an operator on the hilbert space.What I learnt in this thread is that objects are not waves, nor are objects state vectors. I was hoping they were when I delved into Many Worlds for 2 years but realized they were not. So objects are just operators acting on Hilbert space.. in other words.. objects are some kind of programming outputs.. so in times of such desperation.. I think the minimal interpretation makes sense because we may not be able to know what is behind it all (whether the program is written in Fortran or Pink elephant or whatever).. unless Demystifier can show particles we measure are a result of quasiparticle phonon dynamics due to some fundamental particles that have trajectories.. but is this likely.. and if there is no way to prove this.. then we have reached the end of physics.
Hamiltonian includes potential energy term, right? But to specify potential energy you need classical configuration of charges, right?
So don't you need classical description before you can start to talk about QM description?I'm not sure what you mean. In quantum mechanics, the hamiltonian (including the potential) is an operator on the hilbert space.
Let's suppose that we have a Hamiltonian [itex]H[/itex] for the entire universe, and a corresponding Hilbert space of possible pure states.Hamiltonian includes potential energy term, right? But to specify potential energy you need classical configuration of charges, right?
So don't you need classical description before you can start to talk about QM description?
Oh actually first time to hear about this. Ill read Ballentine tomorrow curious to see whats all the fuss about it. Thanks for the tips. Btw do you consider the quantum state as objective or concern only the bayerian and frequentist aspects or side of it? Then you are a genuine Ensemble Interpretation proponent while Vanees71 is more a hybrid Ensembler/Copenhagen right? He believes the quantum state is objective while you are agnostic. We mustn't use categorication from book only or author but from technical consideration. Many thanks.Well, Vanhees says that the quantum state is objective because it is an equivalence class of preparation procedures. That's what I would call subjectve. It seems the same to me as the idea that the quantum state represents our information about the system, which is a subjective notion of the state.
What's weird about QM is that there are two interpretations that people freely switch back and forth between, even though they seem completely different. No, I don't mean Copenhagen versus Many Worlds versus Bohmian.The two interpretations are:
Here's my feeble attempt to bridge the gap between these two interpretations, which I think is compatible with Copenhagen.
Now, we can give the classical dynamics. If the universe starts in the classical state [itex]S_i[/itex] at time [itex]t_1[/itex], then the probability that it will be in classical state [itex]S_j[/itex] at time [itex]t_2[/itex] will be given by:
[itex]P(i,t_1, j, t_2) = sum_lambda p_{i,lambda} langle psi_lambda|Pi_j(t_2 – t_1) |psi_lambdarangle[/itex]
where [itex]Pi_j(t_2 – t_1)[/itex] is the operator [itex]Pi_j[/itex] in the Heisenberg picture: [itex]Pi_j(t_2 – t_1) = e^{+i H (t_2 – t_1)} Pi_j e^{-i H (t_2 – t_1)}[/itex]
This transition function [itex]P(i,t_1, j, t_2)[/itex] in a sense tells us everything we need to know, and everything that we can test experimentally. The details of complex-valued wave functions that evolve unitarily can be seen as just calculational tools for deriving this macroscopic dynamics.
But there are many strange aspects to this macroscopic dynamics, but perhaps that would consume another thread.
In Bohmian Mechanics, are the electron and quark generic identical particle (like a generic marble) that different wave functions (say comprising the electron and quark) act on?They are not.
Also in BM, the wave function is coupled to the quantum potentialNo it isn't.
I know my questions are silly so I won't ask more and let others ask the more non silly important questions. Lol. Thanks..:biggrin: :bow:
Wave function does not distinguish two electrons, in that sense they are identical. But they may have different Bohmian positions, so in this sense they are not identical. It is analogous to the fact that all people are equal under the law, yet each human lives a different life.I was not asking if the particles are the same particles like someone asked earlier if they are just one particle. I mean, since the properties of the electron and quark are in the wave function. In Bohmian Mechanics, are the electron and quark generic identical particle (like a generic marble) that different wave functions (say comprising the electron and quark) act on?
Also in BM, the wave function is coupled to the quantum potential which controls the particle. Let's say they are uncoupled.. or you make the quantum potential null.. then the wave function and particle will be decoupled. Let's use an example of an apple. If the quantum potential is nulled.. would all the particles in the apple just fall into a lump (perhaps the size of a grain).. this is to aid in understanding the connection between the wave function and particles in BM.
I know my questions are silly so I won't ask more and let others ask the more non silly important questions. Lol. Thanks..
Btw.. in conventional Bohmian mechanics… are all the particles identical.. remember it is the wave function that do all the muscles and works.. and it just pushes the particles via the quantum potential.. therefore are the particles in say electron and quark identical particle (in BM) that you can interchange them with no effect?Wave function does not distinguish two electrons, in that sense they are identical. But they may have different Bohmian positions, so in this sense they are not identical. It is analogous to the fact that all people are equal under the law, yet each human lives a different life.
No speed limit at the fundamental level. (Which, as a byproduct, may also solve the the black-hole information paradox.)Are there no quantum gravity researchers or Rovelli or Perimeter Institute folks suggesting this too? The idea is simple and elegant… someone may have thought or suggested it before.. anyone has read a paper at arxiv about this? Trapped by c.. it's going to make us transcend and reach out the stars faster than our medieval relativistic prison.
But then isn't it the fundamental particles are inside the planck scale.. how can it become large scale and no speed limit? And how do they exactly cook up the quasiparticles in the condense matter phonon analogy? Can you write a paper describing their properties at least on a theoretical level?
Btw.. in conventional Bohmian mechanics… are all the particles identical.. remember it is the wave function that do all the muscles and works.. and it just pushes the particles via the quantum potential.. therefore are the particles in say electron and quark identical particle (in BM) that you can interchange them with no effect?
Well, as I said before, I don't believe in a cut as a fundamental property of nature. From todays knowledge I'd say either nature is described (!) entirely by QT and we just lack a satisfying QT of gravity or we need something completely new, making QT an approximation valid in absence of gravity (as special relativity is an approximation in absence of gravity, as far as the classical theory of gravity, i.e., general relativity, is concerned).
The "cut" is thus epistemic too, i.e., it's my decision to choose where to put the cut whenever possible, i.e., whenever the classical coarse-grained description is justified, and it's usually justified at some point in a measurement procedure, because finally we need macroscopic output to be able to observe anything with our poor human senses. It's just a cut in the description but not inherent in Nature.
Of course, as any debate in issues on interpretation, it's more or less a matter of opinion. The only restriction is that an interpretation should not contradict observations, and among the discussed interpretations, in my opinions what's clearly ruled out are "the collapse of the state" (at least with an ontological interpretation of quantum states). Many other interpretations are just adding superfluous assumptions that don't provide any merit compared to the minimal interpretation, e.g., Bohmian trajectories that are not observable, and the Bohmian interpretation imho still has no convincing case for relativistic QFT. In the socalled many-worlds interpretation it's just assumed that all the possibilities inherent in the wave function happen but only one is observed. The socalled "parallel universes" are not observable, and thus in my opinion not subject to objective science since their existence cannot be empirically verified or falsified.
That's right. For a week I kept wondering how the wave function decide to collapse after it is decohered.. my analogy (silly as it is) is like wave function is very sensitive and commit suicide (collapse) when any of its secret is known (or loss phase coherence). I'd continue to think but won't mention in this thread again.
So as not to be off topic. Demystifier idea of our particles like electron, quark as relativistic quasiparticles (like phonons) from condense matter physics is great with the real Bohmian particles as non-relativistic ontology.. actually I first heard of it early this year from his paper… and I'd like to ask Demystifier what is the speed limit of the real bohmian particles.. is it not limited by c? If you don't know. Hope Demystifer can answer this when he gets back. Thanks.No speed limit at the fundamental level. (Which, as a byproduct, may also solve the the black-hole information paradox.)
But the theory shouldn't tell you where to put the cut. It should be able to handle all possible scenarios. It's like asking from classical mechanics to tell you what the forces are, or what coordinates you should use.Classical mechanics does not tell us what the forces are, but it is experiments that tell us what the forces are. On the other hand, experiments do not seem to tell us where the cut is.
Concerning the question what coordinates one should use, this is not a good analogy because in principle any coordinates are OK, except that in some coordinates the problem looks more complicated. By contrast, it is certainly not the case that any cut is OK.
So that makes them higher dimensional than the standard model, but still particles… is that in addition to strings or it constitutes them?In perturbative string theory, branes are solitonic objects. In M-theory, strings aren't there anymore.
I was influenced by Everett who somehow was able to make the state, represented by the statistical operator, really in one-to-one relation with the described object without any collapse. Remember in Many Worlds, the wave function form many worlds where instead of collapse to one eigenstate.. all eigenstate exist.. but I think he has made a trick somewhere. In case you know how Everett did it.. please share how the trick is done in one message and that's it.. I'd no longer ask more in this thread.
Sorry for this novice question. Don't worry when Demystifer returns from his weekend hiatus tomorow.. i'd leave the discussions so experts can make more productive discussions without novices disturbing the tone. Thanks a lot Vanhees71! Btw.. i'm not a philosopher.. but applied science novice..
Let me clarify my point so I’d get a quick answer from those who already know. Wave function is spread out, so it can’t be the particle itself. This was why Born proposed the probability interpretation about a century ago. This was what Vanhees71 was also talking about that’s why he said this was abandoned in 1927. But in Everett Relative State or general Many Worlds. What you have is simply more superposition and entanglement.. but just the same you still have spread out waves in each branch.. so without Born probability square thing.. how does the wave manifest into particle (in each branch)? Can someone who know (like Stevendaryl) please answer this. Thanks.
Most discussions I read in the archives is about how to get Born rule to have worlds existing according to the weight or probability, but nowhere is it mentioned how wave turn into particle in each branch (I've been searching for hours at end. So hope someone can correct my misconception (if you think it’s necessary to reply this in a separate thread, then please create one to avoid watering down the issues in this thread which is about the condense matter quasiparticle thing).
Btw.. In Bohmian Mechanics, the mechanism of how wave manifest as particle is simply the quantum potential that pushes the particle around. Only problem here is it’s difficult to reconcile with QFT where the particle annihilates and creates (the quantum potential only pushes thing around, it doesn’t create or annihilate particles). That’s why I find Demystifier condense matter physics analogy of our relativistic particles as quasiparticles intriguing as it can explain QFT particles. And I’d like to know if there is a way to refute it… so if there is.. and there is no way for BM to explain QFT.. then I have to be stuck to MWI or Copenhagen as most likely (with others Objective Collapse, Cramers/Rastner Transactional, etc. in decreasing order of plausibility or vice versa), and at least we have one less as we eliminate Bohmian Mechanics due to severe inability to be relativistic. Many thanks.
In my opinion the problem is that bluecap and I have different understanding of the words "real" and "objective". First of all, I must admit, I don't know, what philosphers mean by "real" or "realistic interpretation". It's such a mess of different meanings that I like to avoid to use this word, and I don't know where in physics I need it anyway. A better distinction is whether you have an ontological or epistemological interpretation of the quantum state (which in the formalism is represented by the statistical operator): In the ontological version, the philosopher believes that the state, represented by the statistical operator, really is in one-to-one relation with the described object. In my opinion this interpretation has been refuted already in the very early days of modern QT: An electron is observed as a point-particle like object when one makes a position measurement (e.g., by putting a photo plate in its way) but not as a smeared-out continuous charge or mass distribution. That's why Born introduced the probability distribution, and I think that QT is only consistent with all observations and also relativistic causality structure of spacetime if one accepts this probabilistic meaning of the wave function.I was influenced by Everett who somehow was able to make the state, represented by the statistical operator, really in one-to-one relation with the described object without any collapse. Remember in Many Worlds, the wave function form many worlds where instead of collapse to one eigenstate.. all eigenstate exist.. but I think he has made a trick somewhere. In case you know how Everett did it.. please share how the trick is done in one message and that's it.. I'd no longer ask more in this thread.
Sorry for this novice question. Don't worry when Demystifer returns from his weekend hiatus tomorow.. i'd leave the discussions so experts can make more productive discussions without novices disturbing the tone. Thanks a lot Vanhees71! Btw.. i'm not a philosopher.. but applied science novice..
Thus I think the state is epistemic, i.e., it is a concise description of our knowledge about a system due to some preparation procedure bringing the system into this state. This implies that what some Copenhagen flavors of interpretation call "collapse" is just an update about our knowledge when measuring an observable on a system, which after an analysis of the interaction between the system in the measurement apparatus, enables me to associate another state for the system (although very often, the system is simply destroyed by the measurement, e.g., a photon gets absorbed in being registered via the photoeffect which enables its registration by the measurement device like a photoplate or a modern CCD camera).
Another question is, whether there is subjectivity in QT, and I don't think so. It's objectively defined what a quantum state is. It's independent of the individual researcher what it means to prepare a photon with a certain momentum distribution and polarization state, and in principle anybody can objectively prepare photons in the so described state.
The natural sciences don't deal with subjective notions but restrict themselves strictly to objective properties of observable (and quantifiable) phenomena.
I have already stated that Ballentine gets Copenhagen wrong – that is old news. He believes Copenhagenists think the wave function is real. Most versions do not believe that, although you can easily get that view reading some older textbooks.
Vanhees, like me, believes in the Ensemble interpretation which has a different view of what the wave-function is. Its simply the frequentest and Bayesian view of probability rehashed.
This one error does not invalidate that entire excellent textbook and it has bern rehashed over and over again – there is simply no need to keep going over it.
Thanks
BillIn my opinion the problem is that bluecap and I have different understanding of the words "real" and "objective". First of all, I must admit, I don't know, what philosphers mean by "real" or "realistic interpretation". It's such a mess of different meanings that I like to avoid to use this word, and I don't know where in physics I need it anyway. A better distinction is whether you have an ontological or epistemological interpretation of the quantum state (which in the formalism is represented by the statistical operator): In the ontological version, the philosopher believes that the state, represented by the statistical operator, really is in one-to-one relation with the described object. In my opinion this interpretation has been refuted already in the very early days of modern QT: An electron is observed as a point-particle like object when one makes a position measurement (e.g., by putting a photo plate in its way) but not as a smeared-out continuous charge or mass distribution. That's why Born introduced the probability distribution, and I think that QT is only consistent with all observations and also relativistic causality structure of spacetime if one accepts this probabilistic meaning of the wave function. Thus I think the state is epistemic, i.e., it is a concise description of our knowledge about a system due to some preparation procedure bringing the system into this state. This implies that what some Copenhagen flavors of interpretation call "collapse" is just an update about our knowledge when measuring an observable on a system, which after an analysis of the interaction between the system in the measurement apparatus, enables me to associate another state for the system (although very often, the system is simply destroyed by the measurement, e.g., a photon gets absorbed in being registered via the photoeffect which enables its registration by the measurement device like a photoplate or a modern CCD camera).
Another question is, whether there is subjectivity in QT, and I don't think so. It's objectively defined what a quantum state is. It's independent of the individual researcher what it means to prepare a photon with a certain momentum distribution and polarization state, and in principle anybody can objectively prepare photons in the so described state.
The natural sciences don't deal with subjective notions but restrict themselves strictly to objective properties of observable (and quantifiable) phenomena.
Oh actually first time to hear about this. Ill read Ballentine tomorrow curious to see whats all the fuss about it. Thanks for the tips. Btw do you consider the quantum state as objective or concern only the bayerian and frequentist aspects or side of it? Then you are a genuine Ensemble Interpretation proponent while Vanees71 is more a hybrid Ensembler/Copenhagen right? He believes the quantum state is objective while you are agnostic. We mustn't use categorication from book only or author but from technical consideration. Many thanks.Both Vanhees and I advocate the Ensemble interpretation. Why you believe he is some kind of hybrid beats me.
The ignorance ensemble just applies it to the mixed state after decoherence – that's all.
Thanks
Bill
I have already stated that Ballentine gets Copenhagen wrong – that is old news. He believes Copenhagenists think the wave function is real. Most versions do not believe that, although you can easily get that view reading some older textbooks.
Vanhees, like me, believes in the Ensemble interpretation which has a different view of what the wave-function is. Its simply the frequentest and Bayesian view of probability rehashed.
This one error does not invalidate that entire excellent textbook and it has bern rehashed over and over again – there is simply no need to keep going over it.
Thanks
BillOh actually first time to hear about this. Ill read Ballentine tomorrow curious to see whats all the fuss about it. Thanks for the tips. Btw do you consider the quantum state as objective or concern only the bayerian and frequentist aspects or side of it? Then you are a genuine Ensemble Interpretation proponent while Vanees71 is more a hybrid Ensembler/Copenhagen right? He believes the quantum state is objective while you are agnostic. We mustn't use categorication from book only or author but from technical consideration. Many thanks.
""Of course, the quantum state is objective also in the minimal interpretation" so vanhees71 is really a Copenhagenist by heart.I have already stated that Ballentine gets Copenhagen wrong – that is old news. He believes Copenhagenists think the wave function is real. Most versions do not believe that, although you can easily get that view reading some older textbooks.
Vanhees, like me, believes in the Ensemble interpretation which has a different view of what the wave-function is. Its simply the frequentest and Bayesian view of probability rehashed.
This one error does not invalidate that entire excellent textbook and it has bern rehashed over and over again – there is simply no need to keep going over it.
Thanks
Bill
Of course, all I said about the wave function is equally valid for the representation free formulation, which makes QT indeed much more clear.
Of course, the quantum state is objective also in the minimal interpretation. We haven't even discussed about this question in the entire thread yet. The state is operationally defined by an equivalence class of preparation procedures and as such independent of any subjective influence.After analyzing Vanhees71 statements and reading some of the archives for some hours. He is really a Copenhagenist in disguised! Here's why. First Vanhees71 stated.
1. "There is no cut"
2. "Of course, the quantum state is objective also in the minimal interpretation".
But Neumaier stated elsewhere:
"The minimal interpretation is significantly different from any version that deserves (in my view) to be called Copenhagen. In the Copenhagen interpetation (prevailing until the 1970es), each single object is in a well-defined (though possibly unknown) pure state, which collapses to a different state upon measurement. In contrast, in the (much later sensibly defined) minimal, statistical interpretation, the state is a property of the source (i.e., preparation procedure), not of the single quantum object. If you call the minimal interpretation a flavor of Copenhagen then the term ''Copenhagen interpretation'' loses its discriminating meaning."
Reference https://www.physicsforums.com/threa…presented-as-such.850860/page-21#post-5377217
In a bonafide statistical interpretation. The quantum state is not objective. But vanhees71 clearly stated: ""Of course, the quantum state is objective also in the minimal interpretation" so vanhees71 is really a Copenhagenist by heart. And i think its a reasonable view. The pragmatic bonafide statistical interpretation proponents are those who believe only measured statistics in the detectors makes sense.. who blank out what is between emission and detection. Vanhees71 is not this. Id like to know. Are mainstream physicists mostly bonafide statistical interpretation proponents or hidden or unwilling Copenhagists like Vanhees71?
Ballentine does not do that.Yes, Ballentine does do that.
Error 1: In his discussion of the spin recombination experiment, he says that experimental data are inconsistent with Copenhagen.
Error 2: He is wrong in his discussion of the quantum Zeno paradox.
Neither error is incidental, but comes from his fundamental dislike of standard physics.
Is there a way or no way to prove it that outcome occurs right after decoherence?I stated clearly – and will restate it – NO. Von-Neumann proved you can put the quantum classical cut virtually anywhere. As far as I know, and having gone through the proof myself many moons ago, its still valid. Its an unproveable interpretive assumption placing it there. However it solves in one stroke many issues.
Just to be 100% sure on this – you cant do it – you cant prove the cut happens anywhere.
Thanks
Bill
No, that's not what I meant when I said Ballentine says standard physics is wrong. Ballentine claims Copenhagen makes wrong predictions. Thus Ballentine claims quantum mechanics has already been falsified. That is untrue.Ballentine does not do that. Ballentine has two issues I am aware of:
1. He considers the only version of Copenhagen is the one where the wave-function is objectively real. That's poppycock – the vast majority of versions of Copenhagen have the wave-function like Bayesian probability as a kind of rational beings expectation. Its actually pretty close to his Ensemble interpretation except for a different view of probability – one is Baysian – the other frequentest. Many interpretations of QM are like that – just a rehash of arguments about the meaning of probability:
http://math.ucr.edu/home/baez/bayes.html
2. The above is from his otherwise excellent textbook – but gee nobody is perfect and you have to take the book overall – from that viewpoint IMHO its still by far the best text out these – just my view of course. But elsewhere he has made another error – he states decoherence has no bearing in interpretive issues. Rubbish – it has revolutionized our understanding of QM interpretations clearly pinpointing QM's real issue I stated above. But then again Ballentine believes his ensemble interpretation solves all issues anyway. He is correct – but decoherence has deepened our understanding of that and many other interpretations. We also have interpretations like decoherent histories where it's part of the interpretation itself.
Thanks
Bill
Bingo – it doesn't – it just morphed it.
I had a note about my view of locating the classical quantum cut just after decoherence. There is nothing that says you have to do that – its simply, after understanding decoherence it's the most reasonable place to put it – resolving many issues. But it says nothing about it being there.
What it does however is disprove Von-Neumann's infinite regress argument that since there is no place inherently different from any other is to place to cut the only real place that is different – the consciousness of the observer – we now know a place that is different – just after decoherence.Is there a way or no way to prove it that outcome occurs right after decoherence? Because if there is a delay.. it means even when the phase of the system decoheres (when it suffers decoherence), the von-Neumann cut can still be moved.. and if outcome really occurs after decoherence.. does this show the wave function or state vector natural state is coherence and if something decoheres it.. it suddenly collapse? (assuming collapse is correct or let's say we are discussing about collapse instead of MWI or BM).. reminds me of Penrose gravitationally induced collapse where spacetime sorta got destabilized when coherence of the system is lost so the particle collapsed (because spacetime is telling it to collapse?) And again is there a way or no way to prove it that outcome occurs right after decoherence (or locating the classical-quantum cut right after decoherence)?
Its pretty much standard textbook stuff:
https://www.amazon.com/Decoherence-Classical-Transition-Frontiers-Collection/dp/3540357734
Schlosshauer clearly explains what it does solve and what it does not solve.
I will repeat – it does not solve the measurement problem. The problem comes in 3 parts I will not detail (read the book if interested). It solves the first 2 – but stands impotent before the third – technically how does an improper mixed state become a proper one, colloquially why do we get any outcomes at all. There are numerous views on that – mine is – who cares – its just the way nature is. Other have a different view.
Make up your own mind – it does't really affect anything. I have said it before, and will say it again, the value of studying various interpretations is to understand the formalism better – what is it really saying and what is interpretation. A common one is this collapse idea. At first reading of QM you think it has collapse on observation – some textbooks even have it as a postulate. But MW, BM and Stochastic Mechanics all do not have collapse so it cant be part of the formalism – which it isn't, as you will be acutely aware of if you study Ballentine.
Thanks
Bill
Decoherence is a technical trick for pretending to have solved the measurement problem.Bingo – it doesn't – it just morphed it.
I had a note about my view of locating the classical quantum cut just after decoherence. There is nothing that says you have to do that – its simply, after understanding decoherence it's the most reasonable place to put it – resolving many issues. But it says nothing about it being there.
What it does however is disprove Von-Neumann's infinite regress argument that since there is no place inherently different from any other is to place to cut the only real place that is different – the consciousness of the observer – we now know a place that is different – just after decoherence.
Its pretty much standard textbook stuff:
https://www.amazon.com/Decoherence-Classical-Transition-Frontiers-Collection/dp/3540357734
Schlosshauer clearly explains what it does solve and what it does not solve.
I will repeat – it does not solve the measurement problem. The problem comes in 3 parts I will not detail (read the book if interested). It solves the first 2 – but stands impotent before the third – technically how does an improper mixed state become a proper one, colloquially why do we get any outcomes at all. There are numerous views on that – mine is – who cares – its just the way nature is. Other have a different view.
Make up your own mind – it does't really affect anything. I have said it before, and will say it again, the value of studying various interpretations is to understand the formalism better – what is it really saying and what is interpretation. A common one is this collapse idea. At first reading of QM you think it has collapse on observation – some textbooks even have it as a postulate. But MW, BM and Stochastic Mechanics all do not have collapse so it cant be part of the formalism – which it isn't, as you will be acutely aware of if you study Ballentine.
Thanks
Bill
Or standard physics is incomplete, but no one knows for sure yet.No, that's not what I meant when I said Ballentine says standard physics is wrong. Ballentine claims Copenhagen makes wrong predictions. Thus Ballentine claims quantum mechanics has already been falsified. That is untrue.
Further, Ballentine avoids the classical-quantum cut and collapse, leading to wrong physics in his book. The classical-quantum cut and collapse are the clearest indications that quantum mechanics is incomplete. Because of Ballentine's error, some who read his book make wrong arguments in favour of the possible completeness of quantum mechanics.
Making the claim over and over again that the Measurement Problem and/or the Classical/Quantum Cut are issues that have been resolved by techniques such as decoherence is simply factually false. You can ignore the problems for most practical purposes if they don't interest you, but you are mistaken to assume they have been resolved.
But don't take my word for it; read the works of top level physicists who work in the foundations of quantum physics. As Anthony Leggett (winner of the 2003 Nobel Prize) says: Decoherence is a technical trick for pretending to have solved the measurement problem.Decoherence is just scrambling the probability, it doesn't produce outcome like collapse.
I've been trying to understand Vanheez71 position because I'd like to become an Ensembler Intepretation proponent too because all these Copenhagen, MWI, BM seem adhoc and so medieval and I'd love to stop worrying and learn to love orthodox quantum mechanics too. Vanheez71 said "the quantum state is objective also in the minimal interpretation.". How does he treat the problems of outcome? In a few sentences. Can you summarize his views? Is his also the view of mainstream physicists who think the problem of outcome is not necessary? How does outcome occur in Vanheez's Minimal Ensembler Interpretation for single system. Does he believe single systems don't exist as in don't literally exist.. or does he believe it exists and he just wants to block thinking about it so he just focused on the minimum interpretation.? ut in his arguments, he seems to be saying single systems don't exist or does he mean simply not necessary to think of it. What is it he thinks based from those who have discuss with him for many years? I just want to understand it from another choice of words which others can express so I'd understand it better. It would take me a week to read all his messages at the archive. So I'd like some pointers of his main punchline from those who have thoroughly understood him.
And so as not to be off topic. I've been wondering. In Conventional Bohmian Mechanics.. are all the particles identical.. remember it is the wave function that do all the muscles and works.. and it just pushes the particles via the quantum potential.. therefore are the particles in say electron and quark identical particle (in BM) that you can interchange them with no effect.. again remember the properties of the particle are all stored in the wave function or state vector such that when the particle accelerate in the atom, it doesn't lose energy because the energy is in the wave function and by some dynamics with the quantum potential doesn't lose energy, it just push the worker particle around like slave.
Well, there is no cut, at least nobody could empirically prove that there is anything that doesn't follow quantum theory but must be described classically. Classical physics is understood as an effective description of quantum physics for sufficiently coarse-grained observables of macroscopic objects, and decoherence is among the strongest mechanisms at work to let macroscopic objects occur as classical. Another hint is that the classical-quantum cut is artificial and can be often shifted from one part of the description of a system as applicable.Making the claim over and over again that the Measurement Problem and/or the Classical/Quantum Cut are issues that have been resolved by techniques such as decoherence is simply factually false. You can ignore the problems for most practical purposes if they don't interest you, but you are mistaken to assume they have been resolved.
But don't take my word for it; read the works of top level physicists who work in the foundations of quantum physics. As Anthony Leggett (winner of the 2003 Nobel Prize) says: Decoherence is a technical trick for pretending to have solved the measurement problem.
No, it's complaining about a book on mathematics that claims that standard mathematics is wrong! Ballentine claims standard physics is wrong. Sorry, but standard physics is right, and Ballentine is rubbish.Or standard physics is incomplete, but no one knows for sure yet.
Perturbative string theory is just an approximation of M-theory, which contains branes.So that makes them higher dimensional than the standard model, but still particles… is that in addition to strings or it constitutes them?