Fredrik said:
I'm not sure I understand what you're asking, but if you're asking what I think you're asking (why do I think that PBR defines the
statistical view as what HS calls a ψ-epistemic
ontological model?), then I have answered the question several times already. Here it is again: The things they say immediately after
We begin by describing more fully the difference between the two different views of the quantum state [11].
very clearly match the conditions from the HS definitions of the terms ψ-ontic, ψ-complete, ψ-supplemented and ψ-epistemic. Also, reference [11]
is HS.
Look at the two terms with my bold. The "statistical view" is a system interpretation independent of the statistics used in the model, like statistical mechanics. The "ontological model" is a property of the model, independent of the properties of the system itself. hence you are explicitly stating you think the PBR paper defines the model as the system being modeled. This is wrong, which even just the abstract alone makes clear. The PBR paper made no such claim as you have attributed to them here!
To illustrate start with the abstract and move on through the body:
PBR abstract: http://lanl.arxiv.org/PS_cache/arxiv/pdf/1111/1111.3328v1.pdf said:
Another is that even a pure state has only a statistical signicance, akin to a probability distribution in statistical mechanics.
It can't be any more clear. Is the statistics simply a property of the model, as it is in statistical mechanics, or is the statistics a property of the system itself in direct conflict with its meaning in statistical mechanics? The results point to the latter, but does not require all possible theories to define it in terms of statistics, like QM does.
PBR: http://lanl.arxiv.org/PS_cache/arxiv/pdf/1111/1111.3328v1.pdf said:
Some physicists hold that quantum systems do not have physical properties, or that the existence of quantum systems at all is a convenient fiction. In this case, the state vector is a mere calculational device, used to make predictions of the probabilities for macroscopic events.
This explicitly conveys the notion that the model properties are not the properties of the system but properties of the model. This is a model, not system, specific claim. This immediately follows:
PBR: http://lanl.arxiv.org/PS_cache/arxiv/pdf/1111/1111.3328v1.pdf said:
This work, however, proceeds on the assumption that quantum systems - like atoms and photons - exist, and have at least some physical properties. We assume very little about these properties,[...]
Note the term "like atoms and photons" and the explicit use of "quantum
systems", not a "quantum model" of the system? That's why they assume so little about those properties. They are not requiring any particular ontological judgement of what atoms and photons are, only that they have properties that are measurable independent of any model used to characterize or quantify them. They then go on to demonstrate that quantum randomness entails properties that are described by these statistics that are measurable independent of any model used to characterize or quantify them. Hence the notion that ψ-model (QM) statistics is a set of model only properties, not referring to any system properties is false. It's false irrespective of any ontic or epistemic notions you want to attach to it.
Fredrik said:
This doesn't make sense, since you can't make a rational argument about undefined terms, and the authors do leave "property" undefined. I agree that the authors are making assumptions about the system, but it's impossible to use those assumptions in any kind of argument worth discussing. They can be used to provide some motivation for the terminology of HS, but that's it.
I'm finding it increasingly difficult to believe I am on a physics forum of this caliber hearing the term "properties" is an undefined hence meaningless. It's tantamount to saying the term "empirical data" is an undefined hence meaningless.
1) All measurables are properties.
2) A theory (model) may contain properties that are not measurable but needed to produce valid consequences entailing measurable properties.
3) A model may contain properties that the model defines as non-existent in the system being modeled, like randomness in statistical mechanics which PBR demonstrates can't be the case in QM systems, not models.
4) A system may contain properties not contained in the model, or possibly even properties that are not directly measurable.
What ties all this together in a consistent definition of properties? Properties define limits on degrees of freedom. These limits on the degrees of freedom which are empirically accessible as measurements are the empirical data.
Fredrik said:
This is wrong. The statement I made is a mathematical statement, about two different ways (a quantum theory and its ontological model) to assign probabilities to members of some set. We are only talking about sets and probability measures. Reality doesn't enter into it. Empirical justification doesn't enter into it. It's just a matter of whether another theory (the ontological model) can make the same predictions as the first one (the quantum theory), and at the same time satisfy a few mathematical conditions (the ones that make it a ψ-epistemic ontological model for the quantum theory).
My bold: What then is the point of PBR outlining experimental constructs to
Empirical justify it independently from QM. It is completely, totally, and absolutely outrageous to say
empirical justification doesn't enter into it, period. You want to consider "quantum theory and its ontological model" irrespective of the empirical content of the system it describes!
Let's take it as a purely mathematical statement having not empirical bearing. Now look at statistical mechanics, which defines a statistical system which the randomness is a purely mathematical statement which the theory itself defines out of the model. So if ψ-epistemic is a purely mathematical statement why can't a ψ-epistemic model use ψ-epistemic to describe a system which the self same model describes as non-epistemic, just like statistical mechanics? That is exactly the shoes you are in when you so flagrantly throw away empirical data as having any relevance!
Fredrik said:
I don't understand what you're saying, but I have made it clear that I define QM as the framework in which quantum theories are defined, and that the concept of ontological model applies to specific quantum theories in that framework.
Why then have you generalized ψ-epistemic ontic such that the validity of ANY model can be judged on these epistemic/ontic labels? Wait a minute... you said "quantum theories are defined", as in plural. There is only one empirically meaningful QM and it makes no ontological characterizations of anything whatsoever.
Fredrik said:
For example, a quantum theory of a qubit (any quantum theory with a 2-dimensional Hilbert space) might have an ontological model. What this means is that there might exist another theory that makes the same predictions as the quantum theory, and satisfies the mathematical conditions we would expect to be satisfied if we think of λ as a complete list of properties.
What if it was an "ψ-epistemic ontic" model, whatever that means to you, would that rule out the "might (otherwise) exist"? because I still don't have a clue how you are contextualizing ontic/epistemic definition in an meaningful way, for all quantum theories or otherwise.
Fredrik said:
That's a good question. I think the quality of this paper is so low that it's very questionable if it can be discussed at all. I hope their reviewer will force them to rewrite the article substantially before considering it for publication.
Why then is what they said so perfectly comprehensible to me. Even though the terms used had conflicting meanings in general, even within physics, they unambiguously defined perfectly well the context in which they used said terms. Not only was it sensible but, what you could relate only to an external referenced work which the authors had no hand in, made perfect sense in reference to what they said themselves within their own paper.
Hence I see the "gibberish" as an excuse to cherry pick your own interpretation. Perhaps your interpretation makes perfect sense, but you are not providing it like the PBR paper did, only contextualizing the terms and leaving the reader guessing about the extent of the generality intended.