A Criteria for a good quantum interpretation

[PeterDonis]

what arguments make you so certain that there is no way the map can be the territory?

The map is something you construct, and as @Fra points out, when it tells you something that you find to be wrong, you can change it.

You don't construct the territory, and you can't change it if you find it's "wrong"; the very idea of the territory being "wrong" makes no sense.

 

[EPR]

The map is something you construct, and as @Fra points out, when it tells you something that you find to be wrong, you can change it.

You don't construct the territory, and you can't change it if you find it's "wrong"; the very idea of the territory being "wrong" makes no sense.

I believe that a good map can be the territory. If I didn't, I would have to turn away from the scientific method. I am fairly optimistic that we're starting to unravel the mystery of existence. Slowly but steadily.

 

[PeterDonis]

I believe that a good map can be the territory.

Then you are confused. Even a good map is not perfect, and might need to be changed if it turns out to be wrong. As I said, it doesn't even make sense to say that the territory is "wrong". So the map, even a good map, can't be the same as the territory.

If I didn't, I would have to turn away from the scientific method.

The scientific method in no way requires you to believe that the map is the same as the territory. In fact, it requires you to believe the opposite, since all scientific models are tentative and subject to revision as more evidence is obtained which shows ways in which the model is wrong. As already noted, it doesn't even make sense to say that the territory is "wrong".

 

[martinbn]

No, I am also ready to think of other kinds of existence, as long as someone clearly defines what kind of existence it is. For instance, many-worlders give their best to define existence which is totally unlike classical particles and I am open to that possibility too. But minimalists (e.g. minimal statistical ensemblist) don't even try to define it clearly, because if they tried that would ruin their minimalism.

But every time someone quotes Einstein's "The moon isn't there when no one is looking." you take it to mean the same as "The moon doesn't exist.". For example here, you put these words into Mermin's mouth.

 

[Demystifier]

But every time someone quotes Einstein's "The moon isn't there when no one is looking." you take it to mean the same as "The moon doesn't exist.". For example here, you put these words into Mermin's mouth.

Yes, I do that. And I explained why do I do that. Because it's the same according to the most obvious meaning of "to exist" and Mermin does not propose any clearly defined alternative meaning.

 

[martinbn]

Yes, I do that. And I explained why do I do that. Because it's the same according to the most obvious meaning of "to exist" and Mermin does not propose any clearly defined alternative meaning.

As I said earlier, for you "to exist" means to be or to be made of particles with exact positions at any given time. A classical field theory, say electromagnetism, gives you an example of something that exists, the field, which is not made of particles at all. Standard QM gives you another example, particles but no definite positions unless measured. You continue to refuse anything that is different from your philosophy, and interpret others' statements within your world view as if there is no other possibility.

 

[atyy]

https://www.wired.com/2016/05/new-support-alternative-quantum-view/
"As his biographer Abraham Pais wrote: “We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.”"

https://cp3.irmp.ucl.ac.be/~maltoni/PHY1222/mermin_moon.pdf
"“We often discussed his notions on objective reality. I recall that during one walk Einstein suddenlystopped, turned to me and asked whether I really believed that the moon exists only when I look at it.”"

 

[AnssiH]

Matt Leifer gives criteria that any good quantum interpretation should satisfy.
http://mattleifer.info/2006/06/28/p...doA53UMty42JP5dADhA5SDxRjaTMNPkq1i9Ag3WPCwB5Q

Well I was curious about his criteria since I just posted a very simple interpretation here:
https://www.physicsforums.com/threads/a-simple-local-realist-interpretation-of-quantum-mechanics.1000031/

Looks like I satisfy his criteria quite trivially.

I can also briefly discuss the topic of "help us understand why quantum computation works" if anyone is interested...?

-Anssi

 

[AnssiH]

Well I was curious about his criteria since I just posted a very simple interpretation here:
https://www.physicsforums.com/threads/a-simple-local-realist-interpretation-of-quantum-mechanics.1000031/

Looks like I satisfy his criteria quite trivially.

Well it's against the rules of PF to discuss non-published ideas, so you have to go here to discuss the above:
https://www.scienceforums.com/topic/37808-a-simple-local-realist-interpretation-of-quantum-physics/

(Don't worry, there's nothing particularly controversial there, just drawing direct consequences from some concepts we already commonly use in modern physics)

I can also briefly discuss the topic of "help us understand why quantum computation works" if anyone is interested...?

Okay while I'm here, the thing with quantum computation, if you study something like Shor's algorithm , notice that it's a modulus function where the correct answers repeat periodically. It is possible to cast "periodical answers" to a quantum systems in a way that those correct answers represent constructive interference. Basically if you manage to build logic gates that operate under wave mechanics, then all the correct answers appear as stronger signals in the end of the logic gates - you are more likely to get a correct answer than an incorrect one. (And that is why quantum computers don't necessarily give you right answers, unless you ask many times and aggregate the most common answers)

So basically what is happening there is not really any kind of multi-world parallelism or superposition of logical gates where the computer calculates impossible number of calculations at the same time (although you can conceive it as such if you wish), it's more akin to just arranging a very convenient interference pattern that is completely analogous to some algorithm (the very meaning of "quantum computing algorithms"

I guess to give a classical example, it's as if you had to calculate how a complex solar system behaves. Doing this accurately as a simulation involves quite many complex calculations with huge amount of tricky many-body equations. But if you have a machine that contains a completely analogous and actually physical "solar system", and you arrange your questions so that their results are simply demonstrations of the machine doing what it always does, it would seem to give you answers much faster than is possible to calculate. Because, it never calculated anything. Or perhaps easier example, imagine a pachinko simulation, only there's an actual pachinko machine inside to provide the answers.

And that's why it seems to many people that the prime use case for quantum computers will be to simulate quantum systems. Only, they don't "simulate" quantum systems, they are quantum systems, merely casting their answers to other but completely analogous problems.

And that can be explained with pure wave mechanics.

Think about it.
-Anssi

 

[Demystifier]

As I said earlier, for you "to exist" means to be or to be made of particles with exact positions at any given time.

Not necessarily, I'm open to other possibilities too.

A classical field theory, say electromagnetism, gives you an example of something that exists, the field, which is not made of particles at all.

For me, that's a perfectly fine definition of existence.

Standard QM gives you another example, particles but no definite positions unless measured.

I don't insist that positions must be definite. But I insist that something must be definite and that the theory clearly says what that something is. But standard QM is too vague, it does not say at all what the existing thing is.

You continue to refuse anything that is different from your philosophy, and interpret others' statements within your world view as if there is no other possibility.

No I don't. I only refuse those statements which are too vague.

 

[PeterDonis]

This is getting silly.

It certainly is silly when you say something different from what you said before and pretend it's the same:

By association it means that a man walking is not the same entity as a man walking

It means no such thing. Here's what I responded "of course" to:

Would you say that the "map"(model) of a vehicle braking is not the "territory"(a vehicle braking)?

The corresponding statement for a man walking would be: "the map (model) of a man walking is not the same as the man walking". Which of course is true.

Saying that we have found better maps doesn't mean that the map doesn't describe the territory.

Saying that the map describes the territory is not the same as saying the map is the territory. But you made the latter claim.

You have just earned yourself a thread ban.

 

[martinbn]

Not necessarily, I'm open to other possibilities too.For me, that's a perfectly fine definition of existence.I don't insist that positions must be definite. But I insist that something must be definite and that the theory clearly says what that something is. But standard QM is too vague, it does not say at all what the existing thing is.No I don't. I only refuse those statements which are too vague.

OK, but in QM (excluding unusual philosophical positions) the quantum mechanical system, say an electron, exists and is in a certain state, described by the wave function. In general the state will not be such that the position observables have definite values. That should be fine for you, but is not good enough for you. You insist that there should be an observable with a definite value at any given time. And more, you insist that that observable should have a classical analog and name, like position, momentum, energy and so on. For instance if I say that the electron is in the state $|\psi\rangle$ and that the observable $|\psi\rangle\langle\psi|$ has a definite value 1, you wouldn't be happy, because I cannot give you a classical wording for it. But why should it have a classical analog?

 

[martinbn]

https://www.wired.com/2016/05/new-support-alternative-quantum-view/
"As his biographer Abraham Pais wrote: “We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.”"

https://cp3.irmp.ucl.ac.be/~maltoni/PHY1222/mermin_moon.pdf
"“We often discussed his notions on objective reality. I recall that during one walk Einstein suddenlystopped, turned to me and asked whether I really believed that the moon exists only when I look at it.”"

The title of Mermin's paper is " Is the moon there when nobody looks? Reality and the quantum theory ".

Notice what Jordan says on the first page

" “Observations not only disturb what has to be measured, they produce it….We compel [the electron] to assume a definite position…. We ourselves produce the results of measurements.” "

See, there is no question about the existence of the electron. Just the value of the position! What you measure(the position) is not only disturbed but produced. But the electron exists. You definitely don't measure empty space. If you did, how do you know the result is the position of an electron and not something else!

 

[Demystifier]

OK, but in QM (excluding unusual philosophical positions) the quantum mechanical system, say an electron, exists and is in a certain state, described by the wave function.

It's good for a start, but the problem arises when one tries to say how this wave function changes with time. If one says that it always evolves according to the Schrodinger equation, then it leads to many worlds, which could be acceptable for me, but which certainly does not correspond to what you call "standard" QM. So to defend standard QM, you must find a way to avoid many worlds. One strategy of avoiding many worlds is to introduce some kind of wave function collapse, but I think this is not what you would propose (or would you?). Another strategy is to propose that there is something (and I'm not saying that this something must necessarily have classical-like properties) real which is not completely described by the wave function, but that strategy seems to be in contradiction with your sentence above. So my problem is the following: If the state of electron is described by the wave function, then how this state changes with time? Schrodinger equation only? Random collapses too? Schrodinger equation only for wave function but different evolution for an additional variable? Or what?

In general the state will not be such that the position observables have definite values. That should be fine for you, but is not good enough for you. You insist that there should be an observable with a definite value at any given time. And more, you insist that that observable should have a classical analog and name, like position, momentum, energy and so on. For instance if I say that the electron is in the state $|\psi\rangle$ and that the observable $|\psi\rangle\langle\psi|$ has a definite value 1, you wouldn't be happy, because I cannot give you a classical wording for it. But why should it have a classical analog?

Again, you repeat that I insist on something on which I don't insist at all. Please stop this! There are at least 3 highly non-classical interpretations which I find potentially acceptable: many worlds, collapse as in GRW theory, collapse by consciousness. They are potentially acceptable because they are fairly precise about what is real. But the so called "standard" QM is not precise in that sense.

 

[martinbn]

It's good for a start, but the problem arises when one tries to say how this wave function changes with time. If one says that it always evolves according to the Schrodinger equation, then it leads to many worlds, which could be acceptable for me, but which certainly does not correspond to what you call "standard" QM. So to defend standard QM, you must find a way to avoid many worlds. One strategy of avoiding many worlds is to introduce some kind of wave function collapse, but I think this is not what you would propose (or would you?). Another strategy is to propose that there is something (and I'm not saying that this something must necessarily have classical-like properties) real which is not completely described by the wave function, but that strategy seems to be in contradiction with your sentence above. So my problem is the following: If the state of electron is described by the wave function, then how this state changes with time? Schrodinger equation only? Random collapses too? Schrodinger equation only for wave function but different evolution for an additional variable? Or what?

Yes, there are foundational issues with the time evolution in QM, which interpretations try to solve. But it is not related to the existence of objects in standard QM.

Again, you repeat that I insist on something on which I don't insist at all. Please stop this! There are at least 3 highly non-classical interpretations which I find potentially acceptable: many worlds, collapse as in GRW theory, collapse by consciousness. They are potentially acceptable because they are fairly precise about what is real. But the so called "standard" QM is not precise in that sense.

Ok, but can you stop mischaracterizing the non-realist interpretations by saying that according to them nothing exists.

 

[Demystifier]

Ok, but can you stop mischaracterizing the non-realist interpretations by saying that according to them nothing exists.

Fair enough, from now on I can say that non-realist interpretations are called so because they do not talk about what is real, without denying that something is real. I can also say that the Bell theorem is not relevant to such interpretations because the Bell theorem requires an explicit talk about something real. Would that be OK?

 

[martinbn]

Fair enough, from now on I can say that non-realist interpretations are called so because they do not talk about what is real, without denying that something is real. I can also say that the Bell theorem is not relevant to such interpretations because the Bell theorem requires an explicit talk about something real. Would that be OK?

It is still vague. It has to be clear that reality/nonreality in this context refers only to the existence/nonexictence of values of observable, and not as usual to the existence of objects. An interpretation can say that an electron has definite position at any time, another interpretation can say that this is not so unless you measure the position. Both interpretations can say that the electron exists.

 

[Demystifier]

It is still vague. It has to be clear that reality/nonreality in this context refers only to the existence/nonexictence of values of observable, and not as usual to the existence of objects. An interpretation can say that an electron has definite position at any time, another interpretation can say that this is not so unless you measure the position. Both interpretations can say that the electron exists.

Your definition is precise, but it seems to me that it does not capture what one usually means by "non-realist" interpretation. For instance, by your definition many-world interpretation would be a non-realist interpretation, while otherwise it is viewed as a realist interpretation.

 

[martinbn]

Your definition is precise, but it seems to me that it does not capture what one usually means by "non-realist" interpretation. For instance, by your definition many-world interpretation would be a non-realist interpretation, while otherwise it is viewed as a realist interpretation.

I actually don't like this definition because it is not what one would normally expect. But my impression was that this is the way it is used by the foundations/interpretations guys.

 

[atyy]

Bohr: There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about Nature.

 

[Demystifier]

Bohr: There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about Nature.

Yes, I think it's very much in spirit with my #136.

 

[Fra]

There is only an abstract quantum physical description.

And apparently this "abstract quantum physical descriptions", needs the classical world to be formulated.

This is as true as it's a genuine headache, that will not go away with any von neumann towers.

I think Demystifier and other "realists" rather just wants an "ontology", that is compatible with the epistemology or logical positivsm? Its not such much that it has to be classical mechanics ontology, right? If the ontology only needs to be consistent, and not unique, there seems to be no problem. And if you put it this way, I am no longer sure what I am an realist or anti-realist myself. I guess I am both, and the main difference is wether you think the ontologies are timeless or emergent, or wether they are objective or subjective, or "hidden". But they are ontologies nontheless.

/Fredrik

 

[WernerQH]

Bohr: There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about Nature.

So physics, properly speaking, should be considered a part of linguistics? Of socio-linguistics? The way physicists talk about what they think of as "nature" ("reality"?) ?

Bohr has added an air of transcendence to quantum physics. To think that QT must forever remain fundamentally unintelligible for us mortals is just bad philosophy.

 

[Fra]

So physics, properly speaking, should be considered a part of linguistics? Of socio-linguistics? The way physicists talk about what they think of as "nature" ("reality"?) ?

Needless to say, Bohr hardly meant "say" litteraly, it must mean what "knowledge" we can infer about nature via experimental inquiry as opposed to things that can not be justified via experiments. Best understood thinking of nature as a black box. What we can "infer" is thinks like, how does the black box respond to an incoming beam of something for example.

Bohr has added an air of transcendence to quantum physics. To think that QT must forever remain fundamentally unintelligible for us mortals is just bad philosophy.

I do not draw this conclusion? I think some of the original founders, probably know better than anyone else that the inquires about subatomic systems are anchored in a classical laboratory. One you dissect out the mathematics of QM and study the model in isolation, it's easy to forget the empirical foundation.

/Fredrik

 

[bobob]

I don't insist that positions must be definite. But I insist that something must be definite and that the theory clearly says what that something is. But standard QM is too vague, it does not say at all what the existing thing is.

Sure it does. Standard quantum theory tells you that something that exists if some effect we can observe (in principle) depends upon its existence and that we can (in principle) design an experiment that makes use of that definition to predict the outcome of the experiment. If it's not possible to design such an experiment (in principle), then how could nature make use of such an effect that fits any definition of existence? The quest for some interpretation that is philosophically "more satisfying" for some is just that unless the interpretation leads to effects that standard quantum theory is incapable of predicting. I know of no interpretation of quantum theory that does more than start with a preconception of how the world has to be and the proceed to create whatever is necessary just to agree with quantum theory while also doing whatever is necessary to avoid the consequences of those things that would make the interpretation meaningful.

 

[vanhees71]

I don't insist that positions must be definite. But I insist that something must be definite and that the theory clearly says what that something is. But standard QM is too vague, it does not say at all what the existing thing is.

Standard QM says very clearly what's definite (and it's almost a tautology!): What's definite is the state of a quantum system, and it's determined through a preparation procedure preparing the system in this state.

 

[Demystifier]

Standard QM says very clearly what's definite (and it's almost a tautology!): What's definite is the state of a quantum system, and it's determined through a preparation procedure preparing the system in this state.

That's like saying that in standard classical statistical mechanics the definite thing is the probability density $\rho(x,p)$, determined through a preparation procedure and satisfying the Liouville equation. It doesn't answer the following question: What happens with the classical probability density $\rho(x,p)$ when one measures $x$ and $p$? Upon measurement, does $\rho(x,p)$ collapse?

 

[Fra]

What's definite is the state of a quantum system, and it's determined through a preparation procedure preparing the system in this state.

Would you agree that it's determined by an ENSEMBLE of preparations? Ie. The quantum state refers to statistics, not single interactions?

/Fredrik

 

[vanhees71]

That's like saying that in standard classical statistical mechanics the definite thing is the probability density $\rho(x,p)$, determined through a preparation procedure and satisfying the Liouville equation. It doesn't answer the following question: What happens with the classical probability density $\rho(x,p)$ when one measures $x$ and $p$? Upon measurement, does $\rho(x,p)$ collapse?

No. In classical mechanics the state is a point in phase space and since all observables are functions of the phase-space variables all observables always take a determined value. Statistical methods come only in if you want to describe a system where these values are not known. In QT of course that's different, because there's "irreducible randomness", i.e., the values of at least some observables are indetermined and only probabilities for the values are implied by the preparation in any possible state.

Since in classical mechanics the system's phase-space variables always have a determined value, no matter whether you know them or not, upon measuring the before unknown value nothing happens to the system in an ideal measurement which is performed such that you can neglect the change of state of the system upon measurement. Of course, if you didn't know $(x,p)$ before the measurement and measure it, you just adapt your knowledge on the system making $\rho(x,p)=\delta(x-x_{\text{measured}}) \delta(p-p_{\text{measured}})$. This is simply an update adapting the probability distribution of deterministic observable to your knowledge after the measurement.

 

[WernerQH]

I think some of the original founders, probably know better than anyone else that the inquires about subatomic systems are anchored in a classical laboratory.

This has been reiterated a countless number of times. It may sound logical, but does it make sense? We seem to agree on some real world at the classical level, but does this imply that QT can only be formulated using classical concepts? Strictly we wouldn't be allowed even to talk about atoms. They aren't classical, unless you think of "atom" as synonymous with "point mass".

QT is clearly a microscopic theory, and Bohr's insistence thar it must be formulated with classical concepts has held back the search for concepts that are more appropriate than "state preparation" and "measurement". The nuclear reactions in the sun can be succesfully described, yet the standard interpretation of the theory cannot do without "observers" making "measurements". Absurd.