A Copenhagen: Restriction on knowledge or restriction on ontology?

A. Neumaier

Science Advisor
Insights Author
6,043
2,197
It is argued [by Valentini] that one can still recover the standard distribution of configurations on a coarse-grained scale as a result of dynamical evolution
I think such thermalization/equilibrium hidden variable theories might be the last "hope" for a realist account of subatomic physics. If they are proven to fail (i.e. it is demonstrated such thermalization cannot occur)
Valentini's argument is faulty; see this post. Much improved arguments would be needed to prove thermalization.
 

PAllen

Science Advisor
7,540
945
Unfortunately, that reasoning is flawed. If events are spacelike seperated, then a lorentz transformation can make them simultaneous or make either event occur before the other. So, if you assume one event causes the other, you can make a lorentz transform to a frame in which that is false, which requires the event you assumed was the cause to act retrocausally. That is what non-local means.
I assume there there is no causal relationship between E2 and E3 as I defined them, and this was explicitly stated in my post.

The whole point of my post was to argue against lumping together retrocausal models with pure nonlocal models. Others have clarified here some further distinctions and terminology I hadn’t been familiar with. Thus, I learn that my mental model of a pure nonlocal model seems best described by what is called acausal, which emphasizes the lack of causal relation between E2 and E3.

This was all purely in response to @stevendaryl’s classification. I really like his whole argument through this thread, and just was arguing not lumping together acausal and retrocausal.
 
Last edited:

DarMM

Science Advisor
Gold Member
1,343
557
Valentini's argument is faulty; see this post. Much improved arguments would be needed to prove thermalization.
I fully agree, I don't think the required thermalization/equilibrium process has been demonstrated either in nonlocal or retrocausal theories.
 
22
1
For me, this has to do with determinism and the very definition of "observation".

In the broadest possible meaning, observation is an interaction, an exchange of information between the phenomena and the observer. In that sense, there are some phenomena which cannot be observed, for instance because it doesn't interact, because it is beyond a causal horizon or because it's in the future.

Events that are observed acquire some value (or set of values) and become part of a deterministic space, for those which are not observed (or not yet observed) you can assign a probability, they are part of a phase space. For instance, a prediction of some future event exists only as a probability until the event occur and it's measured.

Furthermore, every observable and observed event exists in the past. Then the past can be viewed as deterministic and the future (plus regions behind horizons) is stochastic.
 

A. Neumaier

Science Advisor
Insights Author
6,043
2,197
Then the past can be viewed as deterministic
But the past cannot be observed either, and becomes more and more uncertain as one goes back in time.
 
22
1
But the past cannot be observed either,
Well, the measurement is made in the present, but the information transfered 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)
 
317
18
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

Gold Member
2018 Award
310
187
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.
 

Demystifier

Science Advisor
Insights Author
2018 Award
9,705
2,728
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
 
317
18
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).
 
Last edited:

DarMM

Science Advisor
Gold Member
1,343
557
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:

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:
 
317
18
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

Science Advisor
Gold Member
1,343
557
@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 modelled mathematically, i.e. no hidden variables.
 
317
18
@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 modelled 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.
 
317
18
"The Copenhagen interpretation is basically nonsense". "No thoughtful person still holds to it"

Sean Carroll: at 1:50:30

 

DarMM

Science Advisor
Gold Member
1,343
557
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.
 
317
18
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.
 
317
18
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

Science Advisor
Gold Member
1,343
557
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

Science Advisor
Gold Member
1,343
557
Not you but the other user arguing that Copenhagen interpretation is perfectably reasonable accepting an assumption that is completely unacceptable.
And that assumption is?
 

DarMM

Science Advisor
Gold Member
1,343
557
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
 
317
18
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.
 
317
18
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.
 

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top