Insights How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics - Comments

[vanhees71]

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.

 

[bluecap]

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?

 

[Demystifier]

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.

 

[bluecap]

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..

 

[Demystifier]

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 potential

No 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..

 

[stevendaryl]

Oh actually first time to hear about this. Ill read Ballentine tomorrow curious to see what's 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:

1. QM is a deterministic theory about microscopic systems. (This initial state will deterministically evolve into that state, according to Schrodinger's equation)
   
2. QM is a stochastic (nondeterministic) theory about macroscopic systems. (If you perform this experiment, you will get one of these results, with such and such probabilities)

Here's my feeble attempt to bridge the gap between these two interpretations, which I think is compatible with Copenhagen.

• Let's suppose that we have a Hamiltonian H for the entire universe, and a corresponding Hilbert space of possible pure states.
• Assume for simplicity that our universe is finite.
• Pick a complete basis |\psi_\lambda\rangle.
  
• Assume a finite degree of precision for any measurement of a quantity.
• This implies a countable (or maybe even finite) set of possible distinguishable "classical states" for the universe. Call them S_i
  
• Then presumably the "classical state" of the universe can in principle be defined via a countable (or even finite) indexed collection of projection operators \Pi_j. The meaning of this is that if the universe is in state |\Psi\rangle, then it's in the classical state j provided that \Pi_j |\Psi\rangle = |\Psi\rangle.
• At this point, I have a bit of a problem. To describe the dynamics of classical states, it's not enough to know the projection operator. You also need a density matrix. The operators \Pi_j are massively degenerate; there are many, many microscopic states corresponding to the same macroscopic state. So if all you know is the macroscopic state (which is all we ever can know), then the best we can do is to have a probability distribution on microscopic states. This can be described by the numbers p_{i,\lambda}, the probability that the microstate is |\psi_\lambda\rangle given that the macrostates is i. Or equivalently, it can be described by the density matrix \rho_i = \sum_\lambda p_{i,\lambda} |\psi_\lambda\rangle \langle \psi_\lambda|

Now, we can give the classical dynamics. If the universe starts in the classical state S_i at time t_1, then the probability that it will be in classical state S_j at time t_2 will be given by:

P(i,t_1, j, t_2) = \sum_\lambda p_{i,\lambda} \langle \psi_\lambda|\Pi_j(t_2 - t_1) |\psi_\lambda\rangle

where \Pi_j(t_2 - t_1) is the operator \Pi_j in the Heisenberg picture: \Pi_j(t_2 - t_1) = e^{+i H (t_2 - t_1)} \Pi_j e^{-i H (t_2 - t_1)}

This transition function P(i,t_1, j, t_2) 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.

 

[zonde]

Let's suppose that we have a Hamiltonian H 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?

 

[stevendaryl]

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.

 

[bluecap]

I'm not sure what you mean. In quantum mechanics, the hamiltonian (including the potential) is an operator on the hilbert space.

What I learned 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.

 

[vanhees71]

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 ;-).

 

[stevendaryl]

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.

 

[vanhees71]

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).

 

[stevendaryl]

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.

 

[vanhees71]

I give up. One cannot discuss if there's no standard use of words :-(.

 

[Demystifier]

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.

 

[vanhees71]

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.

 

[Demystifier]

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

 

[bhobba]

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

Nice.

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 have 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

 

[AlexCaledin]

“To ridicule philosophy is really to philosophize.”

“To have no time for philosophy is to be a true philosopher.”

“Consequences must outweigh probabilities” ( - that seems explaining fine tuning )

― Blaise Pascal

 

[bhobba]

“To ridicule philosophy is really to philosophize.”l

To 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's pretty much is what science has done.

You should look up the case of Gauss vs Kant. Kant had this highly sophisticated dialectic that purported to show Euclidean Geometry was true a-priori. Gauss took a different route - he looked at the structure of Euclidean Geometry and showed it was in fact just as consistent, or not consistent as non-euclidean geometry. A completely different approach that made progress while philosophy got nowhere.

Tthanks
Bill

 

[Demystifier]

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.)

 

[bhobba]

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

 

[stevendaryl]

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.

 

[stevendaryl]

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.

 

[AlexCaledin]

... 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?

 

[martinbn]

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.

 

[vanhees71]

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.

 

[vanhees71]

- 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.

 

[fanieh]

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.

 

[stevendaryl]

But who says that the clicks are more real than the particles and fields.

The minimalist interpretation of quantum mechanics seems to do that. I'm sure you've heard it said by many physicists that

"It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it," lead researcher and physicist Andrew Truscott said in a press release.

no elementary phenomenon is a phenomenon until it is an observed phenomenon.

(John Wheeler)

In the minimalist interpretation, we are using quantum mechanics to compute transition probabilities between macroscopic states: We start with a preparation procedure and proceed to a measurement. Quantum mechanics gives probabilities for the various possible measurement results, given the preparation procedure. So in this formulation, it seems to be viewing some things as definite---we chose a definite preparation procedure, we got a definite measurement result. But the microscopic details are not assumed to have definite values. The microscopic details seem to be treated as mere calculational tools for predicting macroscopic outcomes, which are the real things.