Copenhagen: Restriction on knowledge or restriction on ontology?

[jocarren]

But the past cannot be observed either,

Well, the measurement is made in the present, but the information transferred in that interaction always comes from the past.

and becomes more and more uncertain as one goes back in time.

I believe the uncertainty of a distant past event should be the same as a closer one. The information when measured might be more ofuscated though (entropy increased more between event and measurment)

 

[Pleonasm]

In case one gives up the concept of 'physical realism' - a viewpoint according to which an external reality exists independent of observation – and doesn’t insist on thinking about quantum phenomena with classical ideas, quantum mechanics doesn’t unsettle anymore.

Why wouldn't anyone do that, though? To deny the existence of a fixed external reality independent of observation/measurement would amount to madness, in the classical sense of the word, or simply radical relativism.

 

[Lord Jestocost]

To deny the existence of a fixed external reality independent of observation/measurement would amount to madness, in the classical sense of the word, or simply radical relativism.

Modern physics has no need of the hypothesis of a mind-independent reality.

 

[A. Neumaier]

Modern physics has no need of the hypothesis of a mind-independent reality.

Modern physics has no need of the hypothesis of a mind-dependent reality.

 

[Demystifier]

I fully agree, I don't think the required thermalization/equilibrium process has been demonstrated either in nonlocal or retrocausal theories.

Even if there is no general mathematically rigorous proof, it has been demonstrated in various numerical simulations. For a review see https://www.mdpi.com/1099-4300/20/6/422

 

[Pleonasm]

Modern physics has no need of the hypothesis of a mind-independent reality.

Classical mechanics is an axiomatically mind-independent field of inquiry. QM could very well be too. We don't know the correct interpretation, and the Copenhagen interpretation is not as widely accepted as it once was. Sean Carroll conciders it a "kind of a scandal" that it's still the "default" interpretation taught in the QM mechanics textbooks (source: William Lane Craig- Sean Carroll debate).

 

[DarMM]

Even if there is no general mathematically rigorous proof, it has been demonstrated in various numerical simulations. For a review see https://www.mdpi.com/1099-4300/20/6/422

I've read it before, as well as this interesting review/development which I enjoyed:
https://arxiv.org/abs/0911.2823
The numerical results are suggestive and I'm not overly skeptical, I wouldn't be surprised if Bohmian Mechanics has a rigorous equilibrium theorem, but they are a long way off being convincing. Most simulations involve 2D finite volume cases with particular potentials.

However there are some interesting developments. I liked this one:
https://arxiv.org/abs/1108.5496

 

[Pleonasm]

As for ontology vs expistemology which the threadmakers asks about, you would have to answer this question:

Suppose I am a quantum particle walking in the dark. You could not, no matter what instrument, see me and my exact future positioning in the dark, yet you know I am in the dark, so you attempt to measure where I am going. You can via that process derive deterministic equations for the probability of me arrising at a place in time, but that is as good as it gets. If you don't look at me, the equations for my future positions are classically deterministic.

Is the hiddeness of my (exact) motions during measurement ontological or expistemological in such a world, or is the question simply irrelevant?

 

[DarMM]

@Demystifier was asking a specific question about how the Copenhagen (and similar) interpretation avoids nonlocality and what Copenhagen says about the existence of quantities like position and momentum, i.e. are they simply not known outside of measurement or nonexistent.

The answer to both is:

1. It avoids non-locality via multiple sample spaces/counterfactual indefiniteness/contextuality. Different words for the same thing.
2. According to most Copenhagenish views, no. Momentum and position of quantum systems do not exist outside of measurement. Usually it is assumed quantum systems have properties that are not momenta and positions etc, but whatever they are they cannot be modeled mathematically, i.e. no hidden variables.

 

[Pleonasm]

@Demystifier was asking a specific question about how the Copenhagen (and similar) interpretation avoids nonlocality and what Copenhagen says about the existence of quantities like position and momentum, i.e. are they simply not known outside of measurement or nonexistent.

The answer to both is:

1. It avoids non-locality via multiple sample spaces/counterfactual indefiniteness/contextuality. Different words for the same thing.
2. According to most Copenhagenish views, no. Momentum and position of quantum systems do not exist outside of measurement. Usually it is assumed quantum systems have properties that are not momenta and positions etc, but whatever they are they cannot be modeled mathematically, i.e. no hidden variables.

And Schrodingers cat demonstrate how that leads to reductio ad absurdum, while other interpretations such as the Many Worlds interpretations of QM can account for it.

 

[Pleonasm]

"The Copenhagen interpretation is basically nonsense". "No thoughtful person still holds to it"

Sean Carroll: at 1:50:30

 

[DarMM]

And Schrodingers cat demonstrate how that leads to reductio ad absurdum, while other interpretations such as the Many Worlds interpretations of QM can account for it.

I don't see the connection between what I wrote and Schrodinger's cat.

"The Copenhagen interpretation is basically nonsense". "No thoughtful person still holds to it"

That's just rhetoric of little value.

 

[Pleonasm]

That's just rhetoric of little value.

Rhetoric? Another user in here claimed that once external reality assumptions of the copenhagen interpretation is accepted, everything else makes sense. This is a truism. If you accept the unacceptable, everything else will follow naturally in your theory. Carroll is of the opinion that no thoughtful person would accept the assumptions of the Copenhagen interpretation.

 

[Pleonasm]

I don't see the connection between what I wrote and Schrodinger's cat.

Not you but the other user arguing that Copenhagen interpretation is perfectably reasonable accepting an assumption that is completely unacceptable.

 

[DarMM]

Rhetoric? You claimed that once external reality assumptions of the copenhagen interpretation is accepted, everything else makes sense.

I don't recall saying that once the Copenhagen Interpretation is accepted everything will make sense. I was discussing how it treats Classical physical quantities and what it says about locality in Bell's theorem.

Carroll is of the opinion that no thoughtful person would accept the assumptions of the Copenhagen interpretation.

And this is nonsense, because there are several experts in Quantum Foundations, Quantum Information and Quantum Probability theory and several other areas that accept the the Copenhagen view. To dismiss them all as not "thoughtful" is just a rhetorical move. These people have clearly thought deeply about QM.

 

[DarMM]

Not you but the other user arguing that Copenhagen interpretation is perfectably reasonable accepting an assumption that is completely unacceptable.

And that assumption is?

 

[Pleonasm]

And that assumption is?

The proposition below, which is pure rubbish.

Modern physics has no need of the hypothesis of a mind-independent reality.

 

[DarMM]

The proposition below, which is pure rubbish.

Well I agree that @Lord Jestocost said it, but it's not an assumption in most Copenhagen views I have read, e.g. Bub, Healey, Fuchs, Brukner, Zeilinger, etc

 

[Pleonasm]

And this is nonsense, because there are several experts in Quantum Foundations, Quantum Information and Quantum Probability theory and several other areas that accept the the Copenhagen view.

So? There are nutcase physicists who question the bing bang theory. They might score high on an IQ-test and be thoughtful in other areas, but not in cosmology.

 

[Pleonasm]

Well I agree that @Lord Jestocost said it, but it's not an assumption in most Copenhagen views I have read, e.g. Bub, Healey, Fuchs, Brukner, Zeilinger, etc

Not in those exact terms but crazy enough that it doesn't matter how you phrase it.

 

[DarMM]

So? There are nutcase physicists who question the bing bang theory. They might score high on an IQ-test and be thoughtful in other areas, but not in cosmology.

I won't say anything more about this, but people like Asher Peres, Neils Bohr, Jeffrey Bub, Christopher Fuchs, Rudolf Haag and several others are not nutcases. You are engaged in pure rhetoric: "People who disagree with my opinion are not thoughtful at best, nutcases at worst"

Your problem with the Copenhagen interpretation seems to be related to @Lord Jestocost 's opinion on a mind-dependent reality which isn't really a part of Copenhagen type views.

 

[Pleonasm]

¨

Your problem with the Copenhagen interpretation seems to be related to @Lord Jestocost 's opinion on a mind-dependent reality which isn't really a part of Copenhagen type views.

Not "mind" but "observation" dependent reality.

 

[DarMM]

Not in those exact terms but crazy enough that it doesn't matter how you phrase it.

Not anything like that at all is present in most Copenhagen type views. There is no assumption of a mind-dependent reality at all. Nor anything "crazy" like it. If you think otherwise please provide a reference to a standard account of Copenhagen like interpretations that says otherwise.

For example see Matt Leifer's account here, no such assumption (or anything like it) is mentioned (p.7 onward):
http://mattleifer.info/wordpress/wp-content/uploads/2018/05/Lecture26.pdf

 

[Pleonasm]

"You are the only contemporary physicist, besides Laue, who sees that one cannot get around the assumption of reality, if only one is honest. Most of them simply do not see what sort of risky game they are playing with reality—reality as something independent of what is experimentally established. Their interpretation is, however, refuted most elegantly by your system of radioactive atom + amplifier + charge of gun powder + cat in a box, in which the psi-function of the system contains both the cat alive and blown to bits. Nobody really doubts that the presence or absence of the cat is something independent of the act of observation"

Einstein, in a letter to Schrodinger.

 

[DarMM]

That's not a systematic account of the Copenhagen interpretation.

 

[Pleonasm]

That's not a systematic account of the Copenhagen interpretation.

You mean the Schrodingers cat thought experiment?

 

[DarMM]

You mean the Schrodingers cat thought experiment?

No, I mean it is not a systematic account of the Copenhagen Interpretation. Such as the lecture notes of Leifer I provided or Hans Primas's book "Chemistry, Quantum Mechanics and Reductionism"

 

[Pleonasm]

No, I mean it is not a systematic account of the Copenhagen Interpretation. Such as the lecture notes of Leifer I provided or Hans Primas's book "Chemistry, Quantum Mechanics and Reductionism"

So what is the role of observation in the Copenhagen interpretation, if not the one described by Erwin Schrodinger in Schrodingers cat?

 

[Pleonasm]

Schrodinger was in fact so disgusted by the Copenhagen interpretation that he regretted having contributed the deterministic equations of QM (Schrodinger Equation).I don’t like it (quantum mechanics) and I’m sorry I ever had anything to do with it.(Schrödinger)

This is interesting reading:

"But Schrödinger had no better interpretation of the multi-dimensional wavefunction and thus was overpowered in particular during a visit to Bohr’s institute in Copenhagen in September 1926 as described by Heisenberg and in [1]:

• The discussion between Bohr and Schrödinger began at the railway station in Copenhagen and was crried on every day from early morning to late night….It will scarcely be possible to reproduce how passionate the discussion was carried from both sides….After some days Erwin became ill with a feverish cold. Bohr sat on the bed and continued the argument: “But surely Schrödinger, you must see”. But Erwin did not see, and indeed never did see, why it was necessary to destroy the space-time description of atomic processes.

 

[DarMM]

So what is the role of observation in the Copenhagen interpretation, if not the one described by Erwin Schrodinger in Schrodingers cat?

Roughly speaking the same as it is in any probabilistic model. For instance there is an implicit "observer" in stochastic models of stock prices, because the probabilities are adjusted after observations via Bayes's theorem.

The difference between QM and Classical Probability according to the Copenhagen like interpretations is that in the latter one can assume ignorance over some kind of mathematically delineated facts, i.e. there are hidden variables, where as for QM this is not the case. Also in the Quantum case one seems to necessarily disturb the system.

 

[Pleonasm]

Roughly speaking the same as it is in any probabilistic model. For instance there is an implicit "observer" in stochastic models of stock prices, because the probabilities are adjusted after observations via Bayes's theorem.

The difference between QM and Classical Probability according to the Copenhagen like interpretations is that in the latter one can assume ignorance over some kind of mathematically delineated facts, i.e. there are hidden variables, where as for QM this is not the case. Also in the Quantum case one seems to necessarily disturb the system.

Seems? From Heisenbergs uncertainty principle (which Schrodinger rejected to the day he died): "The thought is now, however, that this only partly explains the phenomenon, but that the uncertainty also exists in the particle itself, even before the measurement is made."

Hence Schrodingers cat "paradox"

 

[DarMM]

Seems?

Yes, the probabilities for different contexts are necessarily altered upon measurement.

Of course due to the Kochen-Specker theorem and similar results one cannot simply view this as disturbance in the Classical experimental sense, but that wasn't my claim.

This doesn't lead to any paradox. If the Copenhagen interpretation had an irrevocable issue with Schrodinger's cat it would have been obvious long ago.

 

[Pleonasm]

If the Copenhagen interpretation had an irrevocable issue with Schrodinger's cat it would have been obvious long ago.

The bloody father of QM, Max Plank, certainly thought it was irrevocable, even before Schrodinger's cat was conceptualized.

 

[DarMM]

The bloody father of QM, Max Plank, certainly thought it was irrevocable, even before Schrodinger's cat was conceptualized.

He thought the Schrodinger's cat thought experiment was an irrevocable problem for the Copenhagen interpretation before either that interpretation or the thought experiment existed?

Looks like he took a retrocausal view.

There simply isn't a problem with Schrodinger's cat in Copenhagen. If you want an exposition of why not I'd recommend Richard Healey's "The Quantum Revolution in Philosophy " Chapter 11.

However at a simpler level you can replicate the "Cat paradox" along with Wigner's friend (a development of Schrodinger's cat) in a local Classical model such as Spekkens toy model and clearly see there is no paradox. It just relates to the different information of differently situated observers.

 

[Pleonasm]

He thought the Schrodinger's cat thought experiment was an irrevocable problem for the Copenhagen interpretation before either that interpretation or the thought experiment existed?

Looks like he took a retrocausal view.

There simply isn't a problem with Schrodinger's cat in Copenhagen. If you want an exposition of why not I'd recommend Richard Healey's "The Quantum Revolution in Philosophy " Chapter 11.

However at a simpler level you can replicate the "Cat paradox" along with Wigner's friend (a development of Schrodinger's cat) in a local Classical model such as Spekkens toy model and clearly see there is no paradox. It just relates to the different information of differently situated observers.

It's a paradox if you don't have a warped view of physical reality (at least by classical standards). If you do, it's perfectly consistent. In that sense, Schrodingers thought experiment did not serve much purpose.

"Schrödinger did not wish to promote the idea of dead-and-alive cats as a serious possibility; on the contrary, he intended the example to illustrate the absurdity of the existing view of quantum mechanics".

To no avail (for some at least).