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

[bhobba]

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/dp/3540357734/?tag=pfamazon01-20

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 can't be part of the formalism - which it isn't, as you will be acutely aware of if you study Ballentine.

Thanks
Bill

 

[bluecap]

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 sort of 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/dp/3540357734/?tag=pfamazon01-20

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 can't be part of the formalism - which it isn't, as you will be acutely aware of if you study Ballentine.

Thanks
Bill

 

[bhobba]

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 there - 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

 

[bhobba]

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 can't do it - you can't prove the cut happens anywhere.

Thanks
Bill

 

[atyy]

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.

 

[bluecap]

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?

 

[bhobba]

""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

 

[bluecap]

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

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.

 

[bhobba]

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.

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

 

[vanhees71]

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

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. 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.

 

[bluecap]

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.

 

[bluecap]

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.

 

[haushofer]

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.

 

[Demystifier]

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.

 

[Demystifier]

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.)

 

[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 [itex]H[/itex] 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 [itex]|\psi_\lambda\rangle[/itex].
  
• 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 [itex]S_i[/itex]
  
• Then presumably the "classical state" of the universe can in principle be defined via a countable (or even finite) indexed collection of projection operators [itex]\Pi_j[/itex]. The meaning of this is that if the universe is in state [itex]|\Psi\rangle[/itex], then it's in the classical state [itex]j[/itex] provided that [itex]\Pi_j |\Psi\rangle = |\Psi\rangle[/itex].
• 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 [itex]\Pi_j[/itex] 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 [itex]p_{i,\lambda}[/itex], the probability that the microstate is [itex]|\psi_\lambda\rangle[/itex] given that the macrostates is [itex]i[/itex]. Or equivalently, it can be described by the density matrix [itex]\rho_i = \sum_\lambda p_{i,\lambda} |\psi_\lambda\rangle \langle \psi_\lambda|[/itex]

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_\lambda\rangle[/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.

 

[zonde]

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?

 

[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