Undergrad Find your ideal quantum interpretation

[PeterDonis]

With all due respect, what is actually your problem?

That the intent of the flow chart in the OP is to ask questions that lead to some known interpretation of QM, not to ensure that all logically possible questions that could ever be asked about QM are included. So a suggestion to add questions to the flow chart should include what known interpretation the questions are intended to lead to.

I merely wanted to point out that one can – to say it in a simple way - adopt a solipsistic point of view when reasoning about questions like “Is there a moon…?” or “Is there an electron …?” and so on. A mere addition to the flow chart.

But this makes no difference unless it ends up leading to some known interpretation that isn't on the chart. The instructions in the OP already tell you to interpret each question according to your own intuition; there is no expectation that everyone will interpret each question in exactly the same way, or that if multiple interpretations are possible for some questions, we have to add more questions to distinguish them.

 

[Demystifier]

Should this go on the flow chart somewhere?

No, because I have not attempted to include all the existing interpretations. I included only those that seem to be the most popular ones, that is those that have a relatively large number of supporters. I constructed my solipsistic HV's just for the purpose of the proof of concept. It helps me (and hopefully someone else) to understand interpretations that defend locality by denying reality.

 

[vanhees71]

How does QT in the minimal interpretation describe the state of the solar system?

We only have a single realization of the solar system, which has been prepared once in ancient times.
Hence we cannot apply rules that require a large ensemble of similarly prepared systems.

You should refer to your own interpretation, which you call the "thermal interpretation"! It perfectly describes how quantum theory is applied by usual physicists of all kind. Only those not accepting the very facts we learned from the discovery of quantum theory that Nature is probabilistic have a problem here. Your own interpretation (I'd somehow rename, because it goes far beyond thermal, i.e., equilibrium systems) tells precisely how QT describes the observations done with our senses (very much coarse grained and subjective since a lot of our perception is rather through "data processes" of our brain than physically objective notions) or with all kinds of sophisticated measurement devices (usually much less coarse grained and thus able to resolve the underlying statistical nature of all observables).

The "solar system", described by macroscopic physics (on the most fundamental level by General Relativity but with good accuracy also with good old Newtonian mechanics), is an emergent phenomenon, and what we observed are grossly coarse-grained macroscopic observables which average at any macroscopic moment of time over zillions of quantum- and thermally fluctuating microscopic degrees of freedom. As @bhobba brought it recently to the point in this forum: Already the CMBR and the (very faint) interstellar medium makes the macroscopic position and momenta of the moon classical FAPP and thus together with the well-established conservation laws (baryon number, electric charge, etc) there's no problem to accept that the "moon is there even if no (human?) being is watching it".

 

[vanhees71]

Stephen L. Adler remarks in “Quantum Theory as an Emergent Phenomenon”:

“There are two conventional ways to try to avoid the measurement dilemma just stated. The first is to assert that quantum mechanics has only a statistical interpretation, and should only be applied to describe the statistical properties of multiple repetitions of an experiment, but not to any individual run. However, with the advent of our ability to trap individual particles for long periods, and to manipulate their quantum states (e.g., the particle emerging from the "up" beam in Fig. l d could be run into a trap, and manipulated there), this interpretation of quantum mechanics becomes dubious.”

Well, does he also tell, why it becomes dubious? Usually measurements on single trapped particles also involves averaging/coarse graining of some kind. The ensemble "recycles" just always the same particle to perform the avaeraging.

 

[Demystifier]

With all due respect, what is actually your problem? I never intended to make up my own interpretation. I merely wanted to point out that one can – to say it in a simple way - adopt a solipsistic point of view when reasoning about questions like “Is there a moon…?” or “Is there an electron …?” and so on. A mere addition to the flow chart.

Among the interpretations on the chart, QBism is the closest to this view.

 

[martinbn]

Well, I don't understand the criterion for considering something real or not from that. I would say that the spacetime manifold is as real as fields are.

This is a perfectly valid point as well. I don't have a strong opinion about the more philosophical question. I also don't have a strong opinion about the wave function. I just want to understand what is meant by "the wave function exists". Some, when asked, admit that it is just sloppy language, others say that it exists in the same way as the classical fields, say the magnetic one. I don't understand this last point of view. That is why I was asking.

By the way, when you say that the manifold is as real as the fields, what do you mean by that? There are surely differences, the fields can have energy, can the manifold? Even the mathematical description is different, the fields are described by section of bundles on the manifold, the manifold itself doesn't require the fields, and so on.

 

[stevendaryl]

By the way, when you say that the manifold is as real as the fields, what do you mean by that? There are surely differences, the fields can have energy, can the manifold? Even the mathematical description is different, the fields are described by section of bundles on the manifold, the manifold itself doesn't require the fields, and so on.

I guess I don't know what "real" means to you. That was the point of my question. But I would say that the classical view of the universe is that it consists of a manifold, and on that manifold are fields and particles. So in a reductionist sense, if you know the values of fields at all points in the manifold, and you know the trajectories of all the particles, you know all there is to know about the universe. So in this view, particles, fields and manifolds are real. There are other objects that come into play in studying classical physics, such as probability distributions, hamiltonians, lagrangians, etc. But I would consider these things to be tools used to reason about the universe, but not necessarily part of the universe.

The clearest case of a theory with a distinction between real and nonreal is probability theory. Probabilities are (at least in many applications) not something that exists in the world, but are something that we use to describe the world, and they reflect not only facts about the world, but facts about our knowledge or lack of knowledge.

Coordinates are another example of something that isn't real, but is a tool that we create to help describe things.

 

[stevendaryl]

You should refer to your own interpretation, which you call the "thermal interpretation"! It perfectly describes how quantum theory is applied by usual physicists of all kind. Only those not accepting the very facts we learned from the discovery of quantum theory that Nature is probabilistic have a problem here.

The issues with understanding quantum mechanics have nothing to do with its being probabilistic, in my opinion. It's the ways that quantum mechanics is NOT probabilistic that cause interpretation problems. There are no probabilities in QM until you select a basis. But what does it mean to select a basis? Obviously, there is a subjective answer, which is that if I set things up so that my state of knowledge becomes correlated with some observable, then I can use the corresponding basis to compute probabilities. But that's subjective. It's not an objective notion of probability.

 

[Demystifier]

There are surely differences, the fields can have energy, can the manifold?

If the manifold is endowed with metric described by general relativity, then it has energy.

 

[martinbn]

I guess I don't know what "real" means to you. That was the point of my question. But I would say that the classical view of the universe is that it consists of a manifold, and on that manifold are fields and particles. So in a reductionist sense, if you know the values of fields at all points in the manifold, and you know the trajectories of all the particles, you know all there is to know about the universe. So in this view, particles, fields and manifolds are real. There are other objects that come into play in studying classical physics, such as probability distributions, hamiltonians, lagrangians, etc. But I would consider these things to be tools used to reason about the universe, but not necessarily part of the universe.

The clearest case of a theory with a distinction between real and nonreal is probability theory. Probabilities are (at least in many applications) not something that exists in the world, but are something that we use to describe the world, and they reflect not only facts about the world, but facts about our knowledge or lack of knowledge.

Coordinates are another example of something that isn't real, but is a tool that we create to help describe things.

It seems to me that "real" means the same thing as it does to you, with one difference. You have decided to take one of the mathematical notions, the manifold, away from the rest such as the probabilities, coordinates, hamiltonians and so on, and group it with the physical entities, the fields and the particles. And call it real.

 

[martinbn]

If the manifold is endowed with metric described by general relativity, then it has energy.

How?

 

[vanhees71]

The issues with understanding quantum mechanics have nothing to do with its being probabilistic, in my opinion. It's the ways that quantum mechanics is NOT probabilistic that cause interpretation problems. There are no probabilities in QM until you select a basis. But what does it mean to select a basis? Obviously, there is a subjective answer, which is that if I set things up so that my state of knowledge becomes correlated with some observable, then I can use the corresponding basis to compute probabilities. But that's subjective. It's not an objective notion of probability.

The very formalism of QT rests on probabilistic interpretation(s) of the state $\hat{\rho}$, and indeed to calculate the probability for the outcome of an (ideal) measurement you need to use the (generalized) eigen basis of the operator representing the measured. That's within the formalism of QT not subject to the arbitrariness of any representation. What you measure is determined by the measurement appatus used to measure the observable you want to measure. There's nothing mysterious in this.

 

[Demystifier]

How?

E.g. https://en.wikipedia.org/wiki/ADM_formalism#ADM_energy_and_mass

 

[PeterDonis]

E.g. https://en.wikipedia.org/wiki/ADM_formalism#ADM_energy_and_mass

This only applies to a certain special class of spacetimes. I'm not aware of any notion of "energy" that only involves the metric and is applicable to all spacetimes.

 

[Demystifier]

This only applies to a certain special class of spacetimes. I'm not aware of any notion of "energy" that only involves the metric and is applicable to all spacetimes.

Well, we could say then that at least some geometries have energy. Would that mean for @martinbn that at least some manifolds are "real"?

Moreover, if one gives up diffeomorphism invariance, then one can define gravitational energy-momentum for any gravitational field. See e.g. https://en.wikipedia.org/wiki/Stress–energy–momentum_pseudotensor

 

[PeterDonis]

if one gives up diffeomorphism invariance, then one can define gravitational energy-momentum for any gravitational field.

Not uniquely. There are multiple possible choices of pseudotensor.

 

[Demystifier]

Not uniquely. There are multiple possible choices of pseudotensor.

Fine, does it mean for @martinbn that spacetime manifolds are real but that the nature of their reality is not unique? I'm just trying to understand what does he mean by "real".

Or to make it less abstract, is gravitational wave real in his view?

 

[A. Neumaier]

group it with the physical entities, the fields and the particles.

A field is a mathematical notion. Thus your division is as arbitrary as the one you criticise!

 

[bhobba]

I'm just trying to understand what does he mean by "real".

This is a judgement thing, but I think most physicists think of mass and momentum as real. However mass is a form of energy and momentum like energy is defined by Noether. Fields also via Noether, just the same as particles, have energy and momentum. So I think most physicists think of fields as real. One can also hold Lord Jestocost's view, but I think most physicists think in more usual terms. However it of course is just a convention.

That's the problem with a lot of this stuff, its really hard to pin down. Philosophers like Wittgenstein grappled with it and was led to what for me was a silly position he argued with Turing - its all just a convention. I of course side with Turing but at the time it was thought Wittgenstein won the debate.

Thanks
Bill

 

[PeterDonis]

This is a judgement thing

Yes, and in the context of this thread, it means that, per the directions given in the OP, everyone should use their own intuitive judgment about what is "real" when answering the questions in the flow chart. Arguing over different definitions doesn't appear to be getting anywhere.

 

[bhobba]

Yes, and in the context of this thread, it means that, per the directions given in the OP, everyone should use their own intuitive judgment about what is "real" when answering the questions in the flow chart. Arguing over different definitions doesn't appear to be getting anywhere.

As I mentioned it didn't get Turing and Wittgenstein anywhere. I do not think we will do any better. All I will add is physicists despite the esoteric areas they investigate tend to side with Turing , as do I - but that's just a personal preference.

Thanks
Bill

 

[Lord Jestocost]

But this makes no difference unless it ends up leading to some known interpretation that isn't on the chart. The instructions in the OP already tell you to interpret each question according to your own intuition;

All right! Then I end up with the step “Copenhagenish interpretations” when it is "allowed" to subsume the instrumentalist minimal interpretation under this term.

[EDIT]
Rationale: I don't trust questions and intuitions which "attempt" to infuse the quantum world with a spurious concreteness (classical concepts) for ease of imagination.

 

[DarMM]

Only those not accepting the very facts we learned from the discovery of quantum theory that Nature is probabilistic have a problem here.

I think one should say "Nature is probabilistic without counterfactuals" or something similar. Just "Nature is probabilistic" isn't enough to get Bell Inequalities.

Note: This isn't a disagreement with the minimal statistical view, I just think it's a more accurate summary of it.

 

[microsansfil]

Just "Nature is probabilistic" isn't enough to get Bell Inequalities.

Yep, "The nature is probabilistic" is a metaphysical statement that is irrelevant to physics.

We use probabilities to talk about correlation, and it turns out that the violation of Bell's inequalities shows that quantum correlations have no equivalent in classical physics.

/Patrick

 

[martinbn]

I'm just trying to understand what does he mean by "real".

Well, I was just asking what the meaning of "the wave function exists" was. It is funny that now I have to explain what the meaning of real is (as in "the manifold is real")! Perhaps those that want me to answer whether I think that the manifold is real should say what they mean by real. Or even better, those that say that the manifold is real should explain what they mean by that.

 

[martinbn]

A field is a mathematical notion. Thus your division is as arbitrary as the one you criticise!

Not only mathematical. Even in mathematics it can mean different things.

 

[stevendaryl]

To me, the

It seems to me that "real" means the same thing as it does to you, with one difference. You have decided to take one of the mathematical notions, the manifold, away from the rest such as the probabilities, coordinates, hamiltonians and so on, and group it with the physical entities, the fields and the particles. And call it real.

But a field is by definition a function of a manifold. I don't know how a field can be real without the manifold being real. What is a field without a manifold?

 

[stevendaryl]

The very formalism of QT rests on probabilistic interpretation(s) of the state $\hat{\rho}$, and indeed to calculate the probability for the outcome of an (ideal) measurement you need to use the (generalized) eigen basis of the operator representing the measured. That's within the formalism of QT not subject to the arbitrariness of any representation. What you measure is determined by the measurement appatus used to measure the observable you want to measure. There's nothing mysterious in this.

But what makes a measurement apparatus a "measurement apparatus"? It's either because it helps me (personally) to know what the value of some variable is, or it is because a measurement apparatus amplifies microscopic variables so that they make a macroscopic difference. Either way seems very subjective to me.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

After consideration by the moderators, the thread will remain closed.