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

[Fra]

theory building in physics, which is based on empirical facts and not some epistemological prejudices.

Do you reallly think there is no epistemological prejudices in theory building? I think the idea that all agents infer "empirical facts" in the same way is illusionary.

How can we make say, noise rejection, without epistemological prejudices? For me the current state of the theory IS the "prejudice" and I don't think a prejudice is necessarily irrational. On the contrary, I think the illusion that an ideal theorist has no prejudices at all as naive and fictive.

/Fredrik

 

[vanhees71]

I only say that everything that is not founded in sufficient empirical input is highly unlikely to provide any insights in the sense of natural science.

 

[Fra]

I only say that everything that is not founded in sufficient empirical input is highly unlikely to provide any insights in the sense of natural science.

I can agree to this, but for me the solution is no to be "free of prejudices", but to entertain somewhat rationally evolving prejudices (which I think should be empirically constructed). This is exactly the reason why I seek "constructable theories" withing the context of realistic inference, meaning subject to realistic constraints of an agent, such as limited information capacity.

This was also what I meant in post 23. The two views are not in contradiction, they may even interact. And for me this is an insight. We shouldn't bash one or the other, but perhaps seek to understnad how they support each other. The complementary views are almost like a bootstrapping in the problem of theory building, where one often needs to motivate the primary notions.

/Fredrik

 

[Demystifier]

All physicists seem to care what the world is made of and are interested in studying that.

Only to the point. To demonstrate this, let me present a typical dialogue between a "realist" (R) and a "typical physicist" (TP) how I see them.

TP: The world is made of atoms, which are made of finer objects such as protons, neutrons and electrons.
R: Sure, but what these objects are? For example the electron, is it the same thing as its wave function?
TP: To the best of our knowledge, yes, the electron is nothing else but a wave function.
R: And when we measure the position of the electron, the wave function suddenly collapses, right?
TP: Yes, that's how we describe it.
R: But is the collapse something that really happens?
TP: Well, if we take it literally, then it violates the Schrodinger equation and the principle of locality. So that's probably not what really happens.
R: So what really happens?
TP: We don't know.
R: Fair enough. But do you care about what really happens?
TP: Not really, because this is a philosophical question that currently cannot be decided by an experiment.
R: So you don't really care about what happens with the electron when it is measured?
TP: I care about those aspects which can be decided by measurement, and don't care about those that can't.
R: Right! And since, as you just said, the answer to the question "what really happens with the electron when it's measured" cannot be decided by measurement, it follows that you don't care about this question.
TP: Yes.
R: Fine, but let us also consider the opposite question: What really happens with the electron when it is not measured? By definition, the answer to this question also cannot be decided by measurement, so you don't care about this question either.
TP: Right.
R: But the electron is either measured or not measured, there is no third possibility. Hence you don't care about what really happens with the electron at all, under any circumstances.
TP: Yes, the question "what really happens" is metaphysical and I don't care about metaphysical questions.
R: Fine, so the question "What happens with the electron?" is metaphysical. Is the question "What the electron is?" equally metaphysical?
TP: Yes, it's a question of the same kind.
R: And hence you don't care about the question "What the electron is?".
TP: Exactly.
R: So you care to know that the world is made of electrons and other stuff, but you don't care to know what the electron and other stuff is.
TP: Yes. Well, no. This discussion doesn't make sense, it's just empty philosophy playing with words, and I don't care about philosophy.
R: Fine. And the question "What is the world made of?" is a philosophical question, so you don't care about this question.
TP: This question has scientific and philosophic aspects. I care only about the scientific ones.
R: Good. But from the purely scientific point of view, you cannot say what is the world made of when we don't measure it, because science is based on measurement. Therefore you don't care about the question what is the world made of when we don't measure it.
TP: Yes.
R: But the world is made of something, irrespective of whether we measure it or not. The measurement disturbs its behavior, but the stuff it is made of is the same, whether we measure it or not. Would you agree?
TP: Yes, that's probably true.
R: So you don't care about the stuff the world is made of.
TP: True, because it's a philosophical question.
R: I rest my case.

 

[vanhees71]

The assumption of what's (very unfortunately) called "local realistic theory" is founded solely on prejudices, originating from the belief that our everyday experience with macroscopic matter which lead to very successful classical models for the observed behavior of this matter. Particularly calling only such a "local realistic theory" "complete" is a big prejudice.

On the other hand in 1925/26 modern QT was discovered (based on empirical facts such as the black-body spectrum, the photoelectric effect, Compton scattering, discrete optical spectra related to "atomic structure",...), which clearly contradicts the "local-realism paradigm". There was from 1935 on a very fruitless debate around the EPR paper. It was fruitless, because it wasn't based on clear empirical facts but on the said epistemological prejudices of EPR.

From a scientific point of view the real breakthrough were Bell's ideas, how to test empirically the assumption of "locality and realism" a la EPR, i.e., he made the vague philosophical ideas a precise quantitative predictions about empirical facts based on such a "local realistic theory" versus the predictions of Q(F)T, and we all know the answer. Q(F)T is correct, and local realistic theories are wrong.

In the scientific community that's settled, and now this result can be used to develop new technology. It's now a business of engineers. Though triggered by philosophical prejudices this success is entirely based on making these vague ideas a clear scientific concept based on empirical facts.

In this sense the "philosophical gibberish" lead indeed to a great scientific success, but only after the philosophy has been transformed by Bell to a clear empirically testable prediction, which lead the experimentalist to develop the corresponding technology to realize these empirical tests in their labs.

Today we are in an analogous dilemma with the (scientific!) problem of finding a quantum theory of the gravitational interaction. All attempts are based on purely theoretical speculations without any empirical foundation. For me it's no surprise that there's no success in finding a satisfactory quantum-gravitation theory. It's because there are no empirical hints at what possible quantum effects might be.

 

[Demystifier]

Q(F)T is correct, and local realistic theories are wrong.

Does it mean that locality is wrong? Or that realism is wrong? Or that both are wrong? What's your hunch?

 

[vanhees71]

Since relativistic QFT in its standard form is based on locality (for causality reasons) it's "realism" that's wrong. Under "realism" I understand that all observables take determined values, and this is obviously wrong in all types of QT.

 

[Fra]

R: But the world is made of something, irrespective of whether we measure it or not. The measurement disturbs its behavior, but the stuff it is made of is the same, whether we measure it or not. Would you agree?
TP: Yes, that's probably true.
R: So you don't care about the stuff the world is made of.
TP: True, because it's a philosophical question.

Here I think TP is confused, because, if we would ask...

Would we expect the "response" to a disturbing measurement, to be influenced by what the stuff "is" or is "made of"? I would guess TP would say yes, and then it's not a philosophical question because TPs expectations and thus actions would depend on the answer. Now consider "TPs" friend, who is also a TP that studies him an his experiments, now this "philosophical equation" enters the hamiltonian of the composite system!

/Fredrik

 

[martinbn]

Only to the point. To demonstrate this, let me present a typical dialogue between a "realist" (R) and a "typical physicist" (TP) how I see them.

This dialog only confirms what I said earlier. You mix notions. Already the first answer is meaningless.

TP: The world is made of atoms, which are made of finer objects such as protons, neutrons and electrons.
R: Sure, but what these objects are? For example the electron, is it the same thing as its wave function?
TP: To the best of our knowledge, yes, the electron is nothing else but a wave function.

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.

The rest of the conversation builds on this and introduces further confusions. Now, I don't know if you do this intentionally or not, or you are just being imprecise, but my problem with the foundations of QM is that most of it is just that, introducing confusions like these and then writing papers on "solving" these "problems".

I am not a physicist, let alone a typical one, but I am willing to have the conversation as the TP, and we can see where it leads.

So my answer to the first question would be: "No, the electron is not the same as its wave function."

 

[Structure seeker]

Since relativistic QFT in its standard form is based on locality (for causality reasons) it's "realism" that's wrong. Under "realism" I understand that all observables take determined values, and this is obviously wrong in all types of QT.

Let me quote myself:

In the paper "A system's wave function is uniquely determined by its underlying physical state" [1] it is concluded based on free choice that interpreting the wavefunction as an objective reality is possible

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.

 

[martinbn]

Let me quote myself:

Th link gives a paper on integration of tensor fields! And it doesn't seem related!

 

[Structure seeker]

My fault, sorry. I mean this link: https://iopscience.iop.org/article/10.1088/1367-2630/aa515c

And also wavefunctions evolve locally, only for entangled particles their quantum properties can only be described by their density matrix (a wavefunction describing their combined properties) so measuring that wavefunction here affects also the wavefunction there.

 

[Demystifier]

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.

Not me, it's the TP who wrongly identifies the territory and the map.

 

[martinbn]

Not me, it's the TP who wrongly identifies the territory and the map.

But you put the words in his mouth!

 

[Demystifier]

I am not a physicist, let alone a typical one, but I am willing to have the conversation as the TP, and we can see where it leads.

So my answer to the first question would be: "No, the electron is not the same as its wave function."

OK, let's try!
R: But wave function represents some properties of the electron. Is there another mathematical object that represents electron properties more directly than the wave function?

 

[Demystifier]

But you put the words in his mouth!

The words I put in his mouth represent his actual words. The words I put are the map, while his true words are the territory.

 

[martinbn]

OK, let's try!
R: But wave function represents some properties of the electron. Is there another mathematical object that represents electron properties more directly than the wave function?

The wave function represents the state of the electron. Other mathematical objects, for example some operators, represent the observables.

 

[martinbn]

The words I put in his mouth represent his actual words. The words I put are the map, while his true words are the territory.

Can you quote the exact words and say whe they belong to?

 

[Demystifier]

The wave function represents the state of the electron. Other mathematical objects, for example some operators, represent the observables.

Which of those, the state or the observables, changes with time? Is that change described by a deterministic equation?

 

[martinbn]

Which of those, the state or the observables, changes with time? Is that change described by a deterministic equation?

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?

 

[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.