Nature Physics on quantum foundations

[Demystifier]

I think that's what makes Bell hard to understand for me. I don't understand, why you are after "ontology" when doing physics. As a natural science it's about what can be objectively and reproducibly be observed, and theoretical physics thus looks for generally valid laws from the patterns we observe.

I never understood how someone who thinks this way can, at the same time, be convinced that the Moon is there when it's not observed.

 

[Demystifier]

Bell (and, of course, this year's Nobel laureates) ruled out the idea of photons always having a definite state of polarization that they carry from the source to the detectors. (Unless they take part in conspiracy or superluminal communication.)

When you put it this way, it sounds as if you are suggesting that the mere idea of superluminal communication is a priori non-scientific. Is that what you are suggesting?

 

[WernerQH]

When you put it this way, it sounds as if you are suggesting that the mere idea of superluminal communication is a priori non-scientific. Is that what you are suggesting?

Not a priori - it would be scientific in a Newtonian universe. Today one would have to give up too much of modern physics if one were to take superluminal communication seriously. What I'm suggesting is that photons do not exist, but merely emission and absorption events. (It's a radically nonlocal view that @vanhees71 probably abhors.)

 

[vanhees71]

Exactly that's what I mean. For me with the work of this years Nobel laureats the case is closed. Of course a quantum system always takes a definite pure or mixed state, but observables do not take necessarily determined values, and that's precisely described by QT. I don't need any ontology, only some formalism that precisely describes what's observed.

 

[vanhees71]

I never understood how someone who thinks this way can, at the same time, be convinced that the Moon is there when it's not observed.

The moon is "constantly observed". The CMBR is already sufficient to lead to rapid decoherence to exclude any quantum behavior to be observed on the motion of the moon.

 

[Demystifier]

The moon is "constantly observed". The CMBR is already sufficient to lead to rapid decoherence to exclude any quantum behavior to be observed on the motion of the moon.

How do you know that there is decoherence when no educated scientist observes decoherence? It follows from equations such as Schrodinger equation, but how do you know that those equations correctly describe our world when we don't make observations? Are you saying that theoretical physics can tell us something about what is going with the world even when we don't observe it?

 

[Demystifier]

As a natural science it's about what can be objectively and reproducibly be observed, and theoretical physics thus looks for generally valid laws from the patterns we observe.

Are those laws valid when scientists don't make observations? If yes, how is that scientific if science is only about the objectively observable?

 

[martinbn]

When you put it this way, it sounds as if you are suggesting that the mere idea of superluminal communication is a priori non-scientific. Is that what you are suggesting?

Without a shred of evedence or a working theory it is just wishfull thinking.

 

[vanhees71]

Are those laws valid when scientists don't make observations? If yes, how is that scientific if science is only about the objectively observable?

Of course, why not?

 

[gentzen]

Special Relativity	Quantum theory
1. Relativity Principle	1. No signalling
2. Light Postulate	2. Non-Locality
Absolute simultaneity	Predictability
| V	| V
Relativity of simultaneity	Unpredictability

How to explain something? Just stay silent, in order not to be wrong? Or try to find a better or worse allegory, parable, or analogy, to get some starting point for talking and building intuition.

 

[vanhees71]

Well, if something is found to be unpredictable, then our theories should describe this unpredictability, and so does QT with great success.

 

[A. Neumaier]

What I'm suggesting is that photons do not exist, but merely emission and absorption events. (It's a radically nonlocal view

Events are by definition local. Nonlocal is only their coincidence statistics. Bell excludes a local hidden variable explanation of the latter, but no more.

 

[A. Neumaier]

Of course a quantum system always takes a definite pure or mixed state

Elsewhere you consistently claimed that single quantum systems usually do not have a definite pure or mixed state - since the latter is a property of an ensemble of similarly prepared systems, not of a single system. But now you assign the definite state to each system. What made you change your mind?

 

[Demystifier]

Of course, why not?

Because it's not scientific, there is no experiment showing that things exist when we don't observe them.

Ontology is by definition things that exist even when we don't observe them, and you always say that ontology is not scientific.

 

[WernerQH]

I don't need any ontology, only some formalism that precisely describes what's observed.

Of course a quantum system always takes a definite pure or mixed state

Obviously you do have an ontology, albeit a rather vague one, when you talk about a "system" being in some "state".

Imre Lakatos made this remark in his Lectures on Scientific Method:

I just want to mention that the twentieth century presents us with quantum mechanics developed primarily by Bohr, Schrödinger, Heisenberg and others, according to which certain types of matter sometimes act as if they were waves and sometImes as if they were particles. The whole thing looks again like the Ptolemaic crystal spheres. Since the 1930s, conventionalism has swept through the scientific community once more. Now the majority of physicists believe that scientific theories from quantum mechanics onwards are very much like Ptolemy's theory. The main thing is their predictive effect, and not their truth value.

 

[Demystifier]

What made you change your mind?

The context. His mind is quantum, it changes depending on the question one asks him. Without the question, his mind is in the state in which answers don't have definite values. I wouldn't be surprised if he could even factorize numbers with the Shor algorithm.

 

[Fra]

Ontological. That Bell considers ontology more fundamental than epistemology is particularly clear from his article "Against measurement". I recommend reading this article to everybody who want to understand how Bell thinks.

@Fra I believe this also answers your question.

Ok, then I see essentially one possibly way to makes sense of this (from my view):

It would be to associate the "beables" with the collection of all possible "intrinsic microstates of the agent", defined relative to it's "intrinsic" perspectives, considered the set of all possible observers. Conceptually then I would think of the beables as the "naked" informarton. But of course thse are not directly observable, that is exactly in the sense they are "hidden", they can be "seen" only by inference from a perspective.

This sense of hidden is not in any way related to "ignorance" ,so the only problem for Bell is then that, if the above is true, then bells ansatz made no sense to start with. So maybe he dismissed his own idea due to a flawed ansatz?

This is they way i interpreted also the solipsist HV of Demystifier. This makes sense, but bells inequality is not applicable.

Anyway, I would also think of the "beables" interpreted as above to be a result of intrinisic measurements. So we still have a empistemological perspective. I don't think we have to choose!

/Fredrik

 

[Fra]

I think that's what makes Bell hard to understand for me. I don't understand, why you are after "ontology" when doing physics. As a natural science it's about what can be objectively and reproducibly be observed, and theoretical physics thus looks for generally valid laws from the patterns we observe.

The "ontology" I see, is the "state of knowledge". The record of observations, wether encoded and stored in classical pointers or non-classical ones, is I think related to states of some "hardware". In extrinsic measurement theory, you can get away with not specifying this hardware carefully.

To consider a "measurement" without considering how the results are stored and encoded, and what constraints the encoding hardware has, is I think incomplete. This is why i see ontology and epistemology as both important. I think both are needed. (That's not so say, we should look for naive ontologies)

/Fredrik

 

[Fra]

Exactly that's what I mean. For me with the work of this years Nobel laureats the case is closed. Of course a quantum system always takes a definite pure or mixed state, but observables do not take necessarily determined values, and that's precisely described by QT. I don't need any ontology, only some formalism that precisely describes what's observed.

What about the "ontology" of background spacetime, that you need to formulate QM in the first place? And the "ontology" of classical pointer records?

/Fredrik

 

[CoolMint]

I think that's what makes Bell hard to understand for me. I don't understand, why you are after "ontology" when doing physics. As a natural science it's about what can be objectively and reproducibly be observed,and theoretical physics thus looks for generally valid laws from the patterns we observe.

Yes, 100%. Science can not hope to explain the invisible universal driving force(to stay outside religion we should label this as 'emergent properties/behavior" as is customary now), hence "science it's about what can be objectively and reproducibly be observed"(end of quote).

(Edited)These discussions about interpretations of invisible behavior, can give some sense of 'understanding' but they are still a road to nowhere.

 

[Demystifier]

Yes, 100%. Science can not hope to explain the invisible universal driving force(to stay outside religion we should label this as 'emergent properties/behavior" as is customary now), hence "science it's about what can be objectively and reproducibly be observed"(end of quote).

How did you arrive at those conclusions? By the scientific method, or by philosophy?

 

[CoolMint]

How did you arrive at those conclusions? By the scientific method, or by philosophy?

I just added a paragraph while you responded.

"These discussions about interpretations of invisible behavior, can give some sense of 'understanding' but they are still a road to nowhere."

The science of what happens between measurements does not exist. So, it must be philosophy.

 

[Demystifier]

"These discussions about interpretations of invisible behavior, can give some sense of 'understanding' but they are still a road to nowhere."

Is your philosophic conclusion above (that it's "a road to nowhere") itself a road to nowhere?

 

[vanhees71]

Elsewhere you consistently claimed that single quantum systems usually do not have a definite pure or mixed state - since the latter is a property of an ensemble of similarly prepared systems, not of a single system. But now you assign the definite state to each system. What made you change your mind?

I didn't change my mind. The state represents a "preparation procedure" for a single system, implying probabilities for the outcomes of measurements via Born's rule, and as such the state refers to an ensemble of equally prepared systems since there's no other way to test the probabilistic predictions than by making repeated measurements on such equally prepared ensembles.

 

[vanhees71]

Because it's not scientific, there is no experiment showing that things exist when we don't observe them.

Ontology is by definition things that exist even when we don't observe them, and you always say that ontology is not scientific.

Ontology then is not covered by natural sciences, because natural sciences are about what's observed in nature. That doesn't imply that things don't exist, when not observed.

 

[vanhees71]

What about the "ontology" of background spacetime, that you need to formulate QM in the first place? And the "ontology" of classical pointer records?

/Fredrik

Spacetime models (Galilei-Newtonian, Minowskian, and GR spacetimes) are descriptions about (local) observable events, among them "classical pointer records", no more, no less.

 

[Lynch101]

You are right, it's meaning cannot directly be tested by observation. Beable is a tool for thinking. It is natural for a human mind to think that physical "things" exist even when we don't observe them, and "beable" is a concept referring to exactly such things. It is nevertheless "scientific", in the sense that at least some scientists find it useful in thinking about science. For example, I like to think that the Moon has a round shape even when it isn't observed, so for me the shape of the Moon is a beable. Perhaps you, on the other hand, prefer to think that the Moon has no shape when it's not observed (the shape is not a conserved Noether charge), so for you the shape of the Moon is not a beable.

Is an "observable", therefore, also be a "beable" prior to its being observed or prior to its interaction with a measurement device?

 

[vanhees71]

Let me guess (although I still think that "beable" is a very poorly defined buzz-word): An observable is a beable only, if the system is prepared in a state, where this observable takes a determined value, i.e., it's represented by the projector to the corresponding eigen-value subspace of the corresponding self-adjoint operator, $\text{Eig}(\hat{O},o)$, where $o$ is the determined value of the observable $O$, which is reprsented by the self-adjoint operator $\hat{O}$.

 

[Demystifier]

Ontology then is not covered by natural sciences, because natural sciences are about what's observed in nature. That doesn't imply that things don't exist, when not observed.

Is there scientific evidence that things exist when not observed?

 

[Demystifier]

Is an "observable", therefore, also be a "beable" prior to its being observed or prior to its interaction with a measurement device?

Beables, by definition, exist prior to both observation and interaction with a measurement device. But you seem to imply that any observable is also a beable, which is wrong.

 

[vanhees71]

If there's nothing, nothing will be observed, i.e., observing something is scientific evidence that there is this something. I think this is a pretty empty philosophical discussion once more. What should this be good for?

 

[CoolMint]

Is your philosophic conclusion above (that it's "a road to nowhere") itself a road to nowhere?

No, as I don't promote any particular interpretation. I am only able to recognize the presence of this underlying 'reality' for its observable effects. Interpretations generally shy away from explaining how the magic of single outcome happens even though it obviously does happen. Use the Schoredinger equation, get the probabilities, interpret the outcome. There is still no deep explanation why, so interpretations are more like descriptions with some added unobservale details.

 

[Demystifier]

Let me guess (although I still think that "beable" is a very poorly defined buzz-word): An observable is a beable only, if the system is prepared in a state, where this observable takes a determined value, i.e., it's represented by the projector to the corresponding eigen-value subspace of the corresponding self-adjoint operator, $\text{Eig}(\hat{O},o)$, where $o$ is the determined value of the observable $O$, which is reprsented by the self-adjoint operator $\hat{O}$.

You are trying to define beable by using only the language of standard QM, which is impossible.

 

[Demystifier]

No, as I don't promote any particular interpretation.

So in general it's valuable to use philosophy in science, but it's not valuable to use philosophy in interpretations of QM. Is that what you are saying?

 

[CoolMint]

So in general it's valuable to use philosophy in science, but it's not valuable to use philosophy in interpretations of QM. Is that what you are saying?

I think it is quite safe to assume that this underlying reality does exist between measurements.

Is there scientific evidence that things exist when not observed?