I Ontology is to quantum theory what hardware is to computation theory

[Demystifier]

Are you changing the subject? You know the answers. There is no disagreement between R and TP on this. Most importantly how is this related to ontology?

Please answer the question, you will see soon how this is related to ontology. I just need that YOU explicitly say that (even if I know it), so that you cannot later say that you didn't say it.

 

[martinbn]

Please answer the question, you will see soon how this is related to ontology. I just need that YOU explicitly say that (even if I know it), so that you cannot later say that you didn't say it.

Ok, fine. In the Heisenberg picture the observables depend on time and satisfy the Heisenberg equations.

 

[vanhees71]

Let me quote myself:

So I disagree. You talk about realism as if it must be about the classical point-like properties. But if we accept that reality consists of wavefunctions, that is totally unharmed by the Bell tests.

In relativistic QFT there are no wave functions but quantum fields.

Even in non-relativistic QFT, where a consistent 1st-quantization formulation exists, the wave function has a probabilistic meaning. The idea that it represents, e.g., an electron as Schrödinger thought originally, contradicts basic observations about electrons, and that's how the probabilistic interpretation by Born became unavoidable. Even nearly 100 years later, there's no other interpretation that is consistent with all observations.

 

[vanhees71]

Ok, fine. In the Heisenberg picture the observables depend on time and satisfy the Heisenberg equations.

In the Heisenberg picture the operators that represent observables in the QT formalism are time dependent and their time evolution is, by definition, governed by the full Hamiltonian. This is of little physical significance though since the physically meaningful quantities derived from the observable operators and the statistical operator are independent under arbitrary unitary transformations, which can be time dependent. In other words the physics is independent of the choice of the picture of time evolution.

 

[Demystifier]

Ok, fine. In the Heisenberg picture the observables depend on time and satisfy the Heisenberg equations.

So where does quantum randomness come from?

 

[martinbn]

So where does quantum randomness come from?

How does this relate to ontology! Now i have the feeling that you are just shooting in the dark hoping to hit something.

 

[vanhees71]

Where does the determinism in classical physics come from?

 

[kith]

No, it is not. It doesn't even make sense to say that the electron is the same as its wave function. You are identifying the territory and the map, and they are not the same things.

I agree that a typical physicist would answer this question differently but I think the map-territory distinction becomes murkier as the concepts become more abstract.

For example, I think many physicists don't distinguish between field quantities and the underlying physical system. I had a discussion with @Demystifier and @A. Neumaier about this 10 years ago.

 

[PeterDonis]

let me present a typical dialogue between a "realist" (R) and a "typical physicist" (TP)

You are misrepresenting the TP position. The difference between TP and R is not that R "cares" about ontology while TP does not, but that TP understands that at our current state of knowledge, we do not have good answers to ontological questions, and therefore does not see much point in continuing to beat one's head against the wall about them, while R refuses to admit this and keeps on asking the questions even though we do not have good answers to any of them. Understanding that we currently do not have good answers to certain questions is not at all the same as not "caring" about those questions at all.

 

[Demystifier]

You are misrepresenting the TP position. ... TP understands that at our current state of knowledge, we do not have good answers to ontological questions, and therefore does not see much point in continuing to beat one's head against the wall about them,

If you read the whole dialogue, you will notice that I said that. So I don't think that I misrepresent the TP.

 

[Demystifier]

How does this relate to ontology! Now i have the feeling that you are just shooting in the dark hoping to hit something.

I'm not, just be patient and we will come to that.

 

[Demystifier]

Where does the determinism in classical physics come from?

From the Newton equation.

 

[PeterDonis]

If you read the whole dialogue, you will notice that I said that.

You had TP say there are no good answers, yes. But that's by no means all you had TP say. You had TP say lots of other things that I don't think were appropriate for the TP viewpoint.

What you should have had TP say was something like: "I know you feel compelled to ask these ontological questions. But we currently have no good answers to any of them. So what's the point of discussing them?"

How would you have R answer that?

 

[PeterDonis]

Please answer the question, you will see soon how this is related to ontology. I just need that YOU explicitly say that (even if I know it), so that you cannot later say that you didn't say it.

I'm not, just be patient and we will come to that.

I don't think these sorts of word games are appropriate here. If you have an argument to make, then make it.

 

[martinbn]

I'm not, just be patient and we will come to that.

Assume i give the textbook asnwers to all your questions and get to thw point.

 

[Demystifier]

You had TP say there are no good answers, yes. But that's by no means all you had TP say. You had TP say lots of other things that I don't think were appropriate for the TP viewpoint.

What you should have had TP say was something like: "I know you feel compelled to ask these ontological questions. But we currently have no good answers to any of them. So what's the point of discussing them?"

How would you have R answer that?

R: So you do not care much about ontological questions, because there is no point in discussing them. Am I right?

 

[PeterDonis]

R: So you do not care much about ontological questions, because there is no point in discussing them. Am I right?

TP: No. I have already said that admitting that we have no good answers to certain questions is not the same as not caring about them.

 

[Demystifier]

Assume i give the textbook asnwers to all your questions and get to thw point.

TP: The randomness is in the wave function collapse, which happens during the measurement.
R: But collapse contradicts locality.
TP: No, because collapse is just an update of our subjective knowledge. The collapse is not a change of real physical stuff.
R: But do you assume that real physical stuff exists?
TP: Of course.
R: But Bell proved that if real physical stuff exists, then, during some types of measurements, this real physical stuff necessarily changes in a way which contradicts locality.
TP: Yes, by which he proved that "real physical stuff" does not exist.
R: But you just said that you assume that real physical stuff exists.
TP: The notion of "real physical stuff" is a vague concept without a true relevance to physics.
R: So you don't care about ontology?
TP: Exactly, I'm a serious scientist so I don't care much about the vague notion of "ontology".
R: I rest my case.

 

[vanhees71]

From the Newton equation.

The Schrödinger equation then also implies that QM is deterministic.

 

[Demystifier]

The Schrödinger equation then also implies that QM is deterministic.

So why then QM is probabilistic in a way in which classical mechanics isn't? Where does the difference come from?

 

[vanhees71]

It's in the connection between the formalism and their meaning for the description of observations.

 

[martinbn]

TP: The randomness is in the wave function collapse, which happens during the measurement.
R: But collapse contradicts locality.
TP: No, because collapse is just an update of our subjective knowledge. The collapse is not a change of real physical stuff.
R: But do you assume that real physical stuff exists?
TP: Of course.
R: But Bell proved that if real physical stuff exists, then, during some types of measurements, this real physical stuff necessarily changes in a way which contradicts locality.

Ok.

TP: Yes, by which he proved that "real physical stuff" does not exist.

Nooooo. How is this a textbook answer? You are doing it again! You keep changing the meaning. Noone says that! How could anyone say that Bell proved that electrons dont exist!!!!!!

R: But you just said that you assume that real physical stuff exists.
TP: The notion of "real physical stuff" is a vague concept without a true relevance to physics.

Same here. Not a textbook answer. And i already answered that.

R: So you don't care about about ontology?
TP: Exactly, I'm a serious scientist so I don't care much about the vague notion of "ontology".
R: I rest my case.

!!!

 

[Demystifier]

It's in the connection between the formalism and their meaning for the description of observations.

The problem, of course, is the precise meaning of the word "observation".

 

[vanhees71]

That's what our experimental colleagues do in their labs.

 

[Demystifier]

You keep changing the meaning.

That's why I wanted that YOU speak for the TP, which you refused.

 

[Demystifier]

That's what our experimental colleagues do in their labs.

So one cannot understand the theory in its own terms, without referring to things outside of the theory. For me, it means that the theory is incomplete.

 

[martinbn]

That's why I wanted that YOU speak for the TP, which you refused.

No, you were asking me questions about operators, equations, time dependence. Those are the textbook questions which i dont know why you asked. The moment i said to assume the answers of those you jumped back to the metaphisical ones. These i will answer ask them.

 

[PeterDonis]

TP: The randomness is in the wave function collapse, which happens during the measurement.
R: But collapse contradicts locality.
TP: No, because collapse is just an update of our subjective knowledge. The collapse is not a change of real physical stuff.

Here you are having TP adopt a particular interpretation. Not all TPs will agree with that interpretation.

R: But do you assume that real physical stuff exists?
TP: Of course.
R: But Bell proved that if real physical stuff exists, then, during some types of measurements, this real physical stuff necessarily changes in a way which contradicts locality.
TP: Yes, by which he proved that "real physical stuff" does not exist.
R: But you just said that you assume that real physical stuff exists.
TP: The notion of "real physical stuff" is a vague concept without a true relevance to physics.

Now you're having TP contradict himself. Of course you can make TP look silly by putting contradictory words in his mouth. But what relevance does that have to anything?

TP: Exactly, I'm a serious scientist so I don't care much about the vague notion of "ontology".

You evidently failed to read my TP response to your earlier question along these lines.

 

[Demystifier]

No, you were asking me questions about operators, equations, time dependence. Those are the textbook questions which i dont know why you asked. The moment i said to assume the answers of those you jumped back to the metaphisical ones. These i will answer ask them.

The question of ontology is a metaphysical one, I cannot talk about it without metaphysics.

 

[vanhees71]

So one cannot understand the theory in its own terms, without referring to things outside of the theory. For me, it means that the theory is incomplete.

Obviously we understand the standard theories of physics well enough to compare their predictions to observations. In this sense they are complete as long as there are not observations which cannot be satisfactorily described by these theories.

 

[Demystifier]

You evidently failed to read my TP response to your earlier question along these lines.

So you care, but admit that you cannot answer it. I'm fine with that, but that's not a typical answer by physicists.

 

[martinbn]

The question of ontology is a metaphysical one, I cannot talk about it without metaphysics.

Yes, and that is fine, i will answer these questions. I onky refuse to answer standard questions about the equation and so on. Go back to where i said noooo about Bell proving that things dont exist and we can resume from there.

 

[martinbn]

TP: The randomness is in the wave function collapse, which happens during the measurement.
R: But collapse contradicts locality.
TP: No, because collapse is just an update of our subjective knowledge. The collapse is not a change of real physical stuff.
R: But do you assume that real physical stuff exists?
TP: Of course.
R: But Bell proved that if real physical stuff exists, then, during some types of measurements, this real physical stuff necessarily changes in a way which contradicts locality.

MBN: So?

 

[romsofia]

I attended a conference on quantum spacetimes this week, and I think there are two relevant things I'd like to add.

One day, the focus was on singularities, and if they needed to be resolved, and if quantum gravity would solve it. Naively, I assumed the field would be split into 2 distinct ideals, but one professor who presented did literature review and found there were actually 4 real attitudes on people who approached the problem, and they were:
1) Singularities are actually resolved in the theories themselves, and they worked on how to show that.
2) Singularities will be resolved in quantum gravity, and they worked on how to show that.
3) Singularities are actually predictions of the theories, so they simply accepted them.
4) Indifference to singularities, these theories aren't fundamental, so the singularities that arise in QFT and GR don't matter.

So, maybe by doing more literature review, you may find there are more than 2 positions on this matter.

Finally, I think it's important to acknowledge something John Bell wrote at the start of his paper titled "The moral aspect of quantum mechanics" in which he stated, "Very practical people who are not interested in logical questions should not read it". If you're not interested in ontology, and the logical questions associated with formalism, don't bother yourself with it. Stick to more practical matters!

 

[PeterDonis]

So you care, but admit that you cannot answer it. I'm fine fine that

Ok.

that's not a typical answer by physicists.

I'm not so sure. I think the physicists you refer to might just not be as patient as I am with "realists" who insist on pestering them with questions that everyone already knows we have no good answers to. Their dismissiveness might not mean they don't care about those questions, but just that they have better things to do with their time than try to explain to "realists" that they don't want to engage in discussions that can never come to any resolution since they're about questions we don't have good answers to.

 

[Structure seeker]

Even in non-relativistic QFT, where a consistent 1st-quantization formulation exists, the wave function has a probabilistic meaning. The idea that it represents, e.g., an electron as Schrödinger thought originally, contradicts basic observations about electrons, and that's how the probabilistic interpretation by Born became unavoidable.

What basic observations contradict this idea?

 

[Demystifier]

MBN: So?

Your view (correct me if I misrepresent it) is that real stuff exists and is "nonlocal" in the Bell sense, which is not in contradiction with the fact that physics is also "local" in another sense. In that sense you and me agree, and it's not at all obvious what do we really disagree about. With intention to clarify the source of our disagreement, let me ask you one additional question. In your view, does this violation of locality in the Bell sense imply a violation of some sort of Lorentz invariance?

 

[Demystifier]

I think the physicists you refer to might just not be as patient as I am with "realists" who insist on pestering them with questions that everyone already knows we have no good answers to. Their dismissiveness might not mean they don't care about those questions, but just that they have better things to do with their time than try to explain to "realists" that they don't want to engage in discussions that can never come to any resolution since they're about questions we don't have good answers to.

I appreciate your patience. Can you try to explain the following to me? If they don't want to engage in such discussions, but still care about these questions, then how is their care manifested?

 

[Demystifier]

Obviously we understand the standard theories of physics well enough to compare their predictions to observations. In this sense they are complete as long as there are not observations which cannot be satisfactorily described by these theories.

Yes, in that sense they are complete. But there is also another sense in which they are not complete. You may call it metaphysical, but whatever you call it, many physicists think that this is important and interesting too.

 

[PeterDonis]

If they don't want to engage in such discussions, but still care about these questions, then how is their care manifested?

There is no useful way to manifest it since the questions are unanswerable at our current state of knowledge and that doesn't appear likely to change any time soon. The best we can do is to continue trying to expand the boundaries of what we can test by experiment, in the hope that eventually that will enable us to find answers for more of these questions.

 

[Demystifier]

There is no useful way to manifest it

So do they manifest it in an unuseful way? If yes, what way is it?

 

[PeterDonis]

So do they manifest it in an unuseful way? If yes, what way is it?

Why do they have to "manifest" it?

 

[martinbn]

Your view (correct me if I misrepresent it) is that real stuff exists and is "nonlocal" in the Bell sense, which is not in contradiction with the fact that physics is also "local" in another sense. In that sense you and me agree, and it's not at all obvious what do we really disagree about. With intention to clarify the source of our disagreement, let me ask you one additional question. In your view, does this violation of locality in the Bell sense imply a violation of some sort of Lorentz invariance?

I expressed my opinion in the very first post i wrote.

No, i think it doesnt imply Lorentz invariance violation.

 

[vanhees71]

Yes, in that sense they are complete. But there is also another sense in which they are not complete. You may call it metaphysical, but whatever you call it, many physicists think that this is important and interesting too.

You never say, what you consider incomplete. That's also typical for philosophical discussions. You keep it nebulous enough just to never end debates about it ;-).

 

[DrChinese]

... I've just come to wonder about whether the phenomenon of entanglement is due to how the wavefunctions of quantum information are "objectively defined". In the paper "A system's wave function is uniquely determined by its underlying physical state" it is concluded based on free choice that interpreting the wavefunction as an objective reality is possible regardless of all the probability involved (contrary to a classical or hidden variable state of a quantum property as proven by the Bell tests). The article poses a thought experiment with an info set $\Lambda$ of complete knowledge of the starting setup, consisting of wavefunctions etc.

Then for instance, it would be easy with two photons ~100% entangled in polarization to explain it such that the wavefunction of polarization of both photons is determined ~100% by the same subset of $\Lambda$.

A link to your reference: https://iopscience.iop.org/article/10.1088/1367-2630/aa515c

The paper is quite similar to (and comes to essentially the same conclusion as) the much better known PBR paper (his reference 14): https://arxiv.org/abs/1111.3328

The psi-ontic and psi-epistemic debate is a complicated subject, and certainly worth the study. But I would like to say something about your statement in bold. You cannot have 2 identical copies of a predetermined entangled wavefunction and get the QM statistical predictions. That is what Bell demonstrated, even though on the surface it appears as if you easily could. (Of course, if there is action at a distance (nonlocality) then all bets are off.)

If that point is not clear from your readings, I would suggest starting a thread in the main QM forum to discuss why. QM is contextual, which means it is dependent on context (the settings of the measurement devices) for its statistical predictions. There are no other known inputs for entangled scenarios with respect to the observed outcomes.

 

[Demystifier]

Why do they have to "manifest" it?

You think that they care, so I assume that they manifest it somehow, for otherwise why would you think that?

 

[PeterDonis]

You think that they care, so I assume that they manifest it somehow, for otherwise why would you think that?

To be precise, I did not say I think they care; I just said I don't think you can infer that they don't care, from the fact that they don't want to engage in endless discussions with "realists". They might just have better things to do with their time.

However, I also do not think caring about something requires "manifesting" that care in a way that you perceive as showing they care. Who made you the judge?

 

[Demystifier]

I expressed my opinion in the very first post i wrote.

No, i think it doesnt imply Lorentz invariance violation.

So you think something exists, and it is nonlocal in the Bell sense, but it does not violate Lorentz invariance. This, indeed, is very textbook like. But I am not satisfied with it, it's too vague for my taste. For example, textbooks say that it is Lorentz invariant because you cannot send signals faster than light. But I'm not satisfied with it, because I don't think that Lorentz invariance is only about sending signals. Bohmian mechanics is a counterexample, where the equations violate Lorentz invariance and yet signals still cannot be faster than light.

The problem with the textbook style explanation is that it does not write down equations that describe how existing things change during the measurement (unless they write down the collapse postulate, which, as an explicit equation, violates Lorentz invariance), so it is impossible to understand mathematically why Lorentz invariance is not violated. Most attempts to write explicit equations of that sort (Bohmian mechanics is an example, but not the only one) lead to violation of Lorentz invariance, but textbooks reject such equations because they are not useful in making new measurable predictions. Since such equations attempt to explicitly describe the existing things, and since textbooks reject it as useless, I see that as a kind of rejection of realism. They still say that something exists, but they reject a need for writing down equations that describe it. Their reason for rejection is - because it does not make new measurable predictions. But their claim that "something exists" also does not make new measurable predictions, so why do they not reject this claim as well? If they are not anti-realists, then they are inconsistent, which for me is even worst. When I think of them as anti-realists, that's because I'm trying to save their consistency.

Any thoughts?

 

[Demystifier]

To be precise, I did not say I think they care; I just said I don't think you can infer that they don't care, from the fact that they don't want to engage in endless discussions with "realists". They might just have better things to do with their time.

However, I also do not think caring about something requires "manifesting" that care in a way that you perceive as showing they care. Who made you the judge?

If they care but not manifest it, then their care is a hidden variable. Would you say that it is justified to think that a hidden variable exists?

 

[TonyStewart]

I have heard of but do not know the many interpretations of QM yet none are definitively Ontological.

Yet the ones that try are: the Copenhagen interpretation and Heisenberg's counter-theory, Many-worlds interpretation, Pilot-wave theory, and String Theory.

Eric Weinstein has boldly stated ST has stagnated progress in TP for at least the last 40 years. He fears but has openly challenged Edward Witten to end the poisoned-well on String Theory (which is useful for QFT) and make way for funding more progress in TP like 100 years ago. Ref Eric & Lex