The quantum state cannot be interpreted statistically?

[Fredrik]

I'm saying the theory you are applying is an incorrect theory to handle the situation you are treating.

That's possible.

To use a correct theory, you must write a joint wave function before you bring the systems together.

I assume that by "joint", you mean "entangled", because what I (and PBR) wrote down are two-qubit states. If we start with different states, then the entire argument goes down the toilet. Even if it can be saved, it would be a very different argument.

But the argument is wrong in quantum mechanics. In quantum mechanics, all identical particles that are treated as being in a pure state are always entangled by their indistinguishability.

The part you have a problem with is certainly not wrong in what I would call "quantum mechanics". You seem to define it as the quantum theory of all particles that actually exist in the real world. This doesn't make sense to me. I define it as the framework in which quantum theories are defined. The usual stuff about the Schrödinger equation is the quantum theory of a single spin-0 particle under the influence of a classical potential. The simplest possible quantum theory is the theory of a single qubit. These theories describe universes where nothing else exists (if they can be said to describe anything at all). The method we use to construct new theories from given ones is part of that framework too.

Well, if we agree it is a bad theory, then what relevance is there in an incorrect application of a correct theory (or a correct application of an incorrect theory, whichever way you choose to think about it)? Either way, it isn't the theory of quantum mechanics.

The relevance is of course that the PBR argument starts with unentangled states like $|0\rangle\otimes|0\rangle$. Isn't that what we're talking about? And it is quantum mechanics.

 

[my_wan]

Yes, but I think Jaynes falls very much victim of his own fallacy. He claims that atoms are real, and it is the mind projection fallacy to claim they are a kind of abstraction! The map is not the territory, but when I look up the term "atom" in the index of a science book, I know quite well that what I will find there is a map, not a territory. Which do you think I will find there? And would Jaynes say that the electrons in my body are real, when quantum mechanics says (quite clearly) that there is no such "real" thing as "the electrons in my body" (being indistinguishable from electrons not in my body)? The fact is, science uses idealizations, and I worry greatly about the depth of scientific understanding of anyone who denies that. I think Jaynes understands probability in scientific epistemology, but probability says nothing about whether or not atoms are real. Indeed, what I would say is that "what is real" in science is whatever the scientist is choosing to regard as real, based on his/her objectives of the moment. Indeed, I would say that is pretty close to undeniable, just look at any scientist in the history of the field, and the ontological notions they embraced to make progress.

Ken, I have justified you position plenty here but noted some personal differences in response to a promise to take us to task on it. It will state those differences as it is directly relevant to the debate this last day. This will also explain what has been falsely attributed to Jaynes falling victim to his own mind projection fallacy. I'll reuse the hurricane analogy to do so.

Suppose, for the moment (I'll loosen this claim later but accept it as factual for the moment), we know that the molecular soup of our atmosphere are indeed ontic (real) entities. We also know that the presents of this hurricane does not represent any new property associated with any of the distinct singular molecules defining it. Now given this state of affairs would you then define the hurricane as an ontologically real entity? Why or why not? In fact you have a philosophical choice here rather than a physical one. Let's look at the consequences of the two choices.

1) If the hurricane is an epistemic construct within these molecules then the claim that the molecules themselves are ontologically real entities may itself be false, and so on and so forth down the reductionist chain to include quantum entities. Such as the wavefunction itself. This, as I have stated previously, begs the question: Is it turtles all the way down. If it is turtles all the way down then it begs the question of whether there exist a bottom, even after a transfinite progression down the reductionist chain. To say that there is no reality beyond an epistemic wavefunction is tantamount to the claim that we hit bottom with no ontic entities anywhere.

2) If this hurricane is an ontologically real entity then even if the molecules in which the hurricane exist in are themselves epistemic constructs it makes the hurricane and the molecules no less ontologically real, so long it is not turtles all the way down. This entails that the wavefunction is an ontologically real entity, however limited our description or characterizations of it may or may not be. Once you allow this hurricane to be ontologically real there is no longer much room for labeling any observables or there characterization as purely epistemic constructs without also claiming it is turtles all the way down.

Of course people labeling themselves realist can fall into a number of categories, with a very broad distinction corresponding to ontic realist verses epistemic realist. An self described epistemic realist can also be an ontic realist by accepting that it is not turtles all the way down but take it as a pragmatic limit of what we can know. Alternatively a self described epistemic realist can reject an ontological foundation, and/or differing epistemic/ontologically positions wrt the hurricane and take the hurricane as real without accepting an ontically real underpinning at the bottom of the turtles. The variations thereof can be bewildering.

Personally, I operate on the presumption that it is not turtles all the way down, that there exist an ontic building blocks of some sort (likely transfinite) lacking any properties other than existing, where all properties are emergent constructs analogous to the way the hurricane is an emergent property. And I remain ambivalent toward the choice of definition as to whether a hurricane in itself is ontic or epistemic. It is merely a partitioned set of properties of a property set which are not more generally partitioned or partitionable in such a manner.

--------
Given these symmetries Jaynes view is not necessarily self contradictory. It doesn't even require the claim that it is not turtles all the way down, only that a hurricane is a physical entity in itself. Yet there is some contradictory elements to the definitions as they have evolved with physics. If you hold that by definition the classical world in which we interact consist of physical variables, knowing that they are derivative variables in some sense analogous to the hurricane, then it requires defining the hurricane as a physical entity in its own rite. To then deny a physical status in some sense to the wavefunction is then incongruent with the previous claim that you live in a physically defined world.

Note: I have blurred the distinction between map and territory here. This I justify not by the legitimacy or completeness of the map, but by the fact that there presumable is a territory (ontic and/or epistemic) in which the map refers. Otherwise the claim that legitimacy (not truth of) of the map is predicated on the limited empirical responses (experiments) of the territory is moot.

 

[Ken G]

The part you have a problem with is certainly not wrong in what I would call "quantum mechanics". You seem to define it as the quantum theory of all particles that actually exist in the real world.

No, that would be a completely impossible theory to use. I define it as a theory of all particles that matter in a given problem, and that is where it is misapplied in the problem you are considering. You are treating two independent qubits, then asking what happens when they come together. There is an illusion there that when they come together, they become entangled, whereas they weren't before, and that seems strange. But that is not the case-- if the particles are to come together, then quantum mechanics must treat the whole system from the start, or at least must choose a treatment that is consistent with that more complete description of the system. It's not like they are separate systems that become one, there is no such "real" thing as a "separate system", and whether or not one can use quantum mechanics to treat them as separate systems is very much dependent on whether or not they ever come together.

This doesn't make sense to me. I define it as the framework in which quantum theories are defined. The usual stuff about the Schrödinger equation is the quantum theory of a single spin-0 particle under the influence of a classical potential.

Subject to additional assumptions, like the spin-0 particle doesn't have any indistinguishable other particles in the vicinity. Quantum mechanics is fully capable of handling the case where there are such particles, but it's not the quantum mechanics treatment you are writing. QM isn't a single treatment, it is a single theory that constitutes many possible treatments, based on the idealizations chosen (so is classical physics, but QM throws in the wrinkle of indistinguishability). The physicist, having chosen to use quantum mechanics, must still tailor the treatment to the situation. Single-particle qubits are a very narrow form of treatment, useful in many situations, but not in the situation you are considering, unless the entanglement is recognized as being there from the start.

The simplest possible quantum theory is the theory of a single qubit.

Yes, and we should always choose the simplest possible treatment that works, but this one doesn't work. Choosing a joint wavefunction would work, though if we want to use pure states, additional information about the initial coherences is required. (Whether or not a joint wavefunction constitutes an entanglement is a tricky issue-- when we write a multiple-electron wavefunction as a Slater determinant, are those electrons entangled? We speak of valence electrons and so on, behaving rather independently of the rest of the electrons, yet we still have the Pauli exclusion principle that keeps the valence electron from falling down to the ground state. It certainly isn't entanglement in the sense that I can measure the spin of the valence electron and constrain the spin of the rest of the electrons.)

These theories describe universes where nothing else exists (if they can be said to describe anything at all). The method we use to construct new theories from given ones is part of that framework too.

Sure, but you were talking about two qubits, not one, and bringing them together. That's not a universe where nothing else exists, it's a universe where something else exists and that something can be brought together.

The relevance is of course that the PBR argument starts with unentangled states like $|0\rangle\otimes|0\rangle$. Isn't that what we're talking about? And it is quantum mechanics.

I presume the entanglement they achieve is the same as they'd have had they simply used a joint wavefunction from the start. I haven't looked closely at those technical details, I'm still trying to figure out if their proof iself is saying anything important, or if it is only their intepretation (or over-interpretation) of it that is of potential significance.

 

[Ken G]

To say that there is no reality beyond an epistemic wavefunction is tantamount to the claim that we hit bottom with no ontic entities anywhere.

Yes, and do you see a problem with that? I see none, that seems like a perfectly natural conclusion to me. I would also argue that there is absolutely nothing that happens in science that requires anything different, nothing that is any different if there are ontic entities anywhere, or if there is not. Science is precisely the same either way, so I argue that science has nothing to add to the issue, nor any interest in adding anything. That doesn't mean science doesn't use ontic entities-- it uses them as pictures, with no concern whatsoever for whether or not they are true or real or absolute in any way. This is quite fortunate, or science would never have even gotten off the ground in millennia past where the ontic elements were terribly ill-conceived in comparison to the ones we use today. This is also the reason that we still use ontic elements, like position and momenta, or forces of gravity, or action at a distance-- even after we have discovered that these ontic elements are not actually ontic at all in our universe.

An self described epistemic realist can also be an ontic realist by accepting that it is not turtles all the way down but take it as a pragmatic limit of what we can know.

The way I would put that is, an epistemic realist views ontic realism as a kind of useful fantasy. This should not surprise us, we start building useful fantasies from childhood. Scientists build more sophisticated useful fantasies, like the concept of a "fluid" even when we know many applications will require the atom concept, or the concept of "atom" even when we know that many applications will benefit more from the field concept, or the concept of "field" when we know that many applications will benefit from a virtual particle concept, or the concept of "virtual particle" when we know that many applications will require nonperturbative treatments. It's concepts, not turtles, all the way down, because that's all we get-- useful concepts. What else is there? What the heck is an "ontic entity" anyway, that isn't the same thing as a useful concept? And please tell me what "ontic entity," chosen from any in the history of science (other than new ones whose limitations we still don't yet know) is not shown up to be an idealization at some deeper level of investigation. As a random example to demonstrate this, consider the seemingly ontological question: does the Earth have a surface?

Personally, I operate on the presumption that it is not turtles all the way down, that there exist an ontic building blocks of some sort (likely transfinite) lacking any properties other than existing, where all properties are emergent constructs analogous to the way the hurricane is an emergent property.

And that is a perfectly valid stance to take, expressly because you recognize it is just a stance. Can Jaynes say the same? Not from the way his position is being characterized on this thread, and that does seem to be an accurate portrayal. He seems to believe that he is not choosing a philosophy, he is holding to truth. This is rather inconsistent behavior from someone who recognizes the pitfalls of mind projection!

If you hold that by definition the classical world in which we interact consist of physical variables, knowing that they are derivative variables in some sense analogous to the hurricane, then it requires defining the hurricane as a physical entity in its own rite. To then deny a physical status in some sense to the wavefunction is then incongruent with the previous claim that you live in a physically defined world.

I'm not sure what you mean by a "physically defined world". It isn't the world that is defined physically, because the world (for the realist) is not defined at all, except in the vaguest possible terms (like "point" in geometry). What is defined is the physicist's effort to understand the world, so we should not say a "physically defined world", we should say a "world that we benefit from attempting to define physically, recognizing that we can do this in very many ways, have done it in very many ways in history, and will likely continue to do in very many ways going forward." What's more, I would point out that in the history of physics, we see a very clear trend toward convergence in accuracy and generality of our predictions. But ask yourself this: do we see a similar convergence in the ontological constructs? Forces, spacetime manifolds, virtual particles, strings... where's the ontic convergence? Nowhere, it is a complete myth. And we are supposed to be the myth-breakers!

Note: I have blurred the distinction between map and territory here. This I justify not by the legitimacy or completeness of the map, but by the fact that there presumable is a territory (ontic and/or epistemic) in which the map refers.

I have no problem with asserting that there is a territory to which the map refers, that's basic realism. My issue is with confusing attributes of the map with attributes of the territory. There is just no such thing as an attribute of a territory-- all attributes are attributes of a map. That's Jaynes' mistake in a nutshell-- he seems to think he can tell the difference between the attributes of a map and the attributes of a territory, and his only criterion for doing so appears to be, if he believes it, it is an attribute of the territory. Logically, there is no justification for drawing that distinction, I'd love to hear someone try to navigate that logical morass. You can't have it both ways-- if there are mind projection fallacies, then the map is not the territory, and if the map is not the territory, then the attributes are found on the map. The territory is just the territory, it cannot have attributes without creating inconsistency of language.

 

[my_wan]

Yes, and do you see a problem with that? I see none, that seems like a perfectly natural conclusion to me.

Wait a minute. There is a contextual reason I required an assumption in the first sentence of my second paragraph and labeled it factual, in spite of explicitly stating I had no intention of maintaining that assumption as factual.

You pulled that quote out of the explicit context or assumptions under which it applied. It applied if and only if viewed under the context 1) provided. Hence to pull it out of that context and say you see a problem while ignoring that context is meaningless. It likes saying if A then B, and you arguing that it's invalid because you disagree with B, irrespective of whether B would result from A or not. I did not claim B, I said IIF A then B.

That post was explicitly constructed as a comparative description of the various perspectives, and not a judgement call on which of those perspectives were valid, true, or any other judgement, scientific or otherwise, on these various perspectives. With the one exception you mentioned below that I'll get to when I come to it.

I have my own perspective I'll discuss separately, which is at odds with the opinion you give here, but only if you recognize the context under which the above statement applied and recognize that by my having an opinion does not constitute a validity judgement on differing perspectives. In pulling that naked quote out of context I have no confidence those conditions are met, and your argument replacing the contextual perspective with your own is moot under the assumptions of the perspective it was intended to apply to.

The way I would put that is, an epistemic realist views ontic realism as a kind of useful fantasy.

Again, I am explicitly comparing the general class of all ontological perspectives for the explicit purpose comparative analysis, whether I personally share that perspective or not. Hence for you to object solely within the narrow range of your own perspective is just as moot as my personal perspective was in the comparison. Pulling a naked quote out and objecting is trivial when many of the perspectives provided are quiet at odds with even my own perspective. Reread it and get the context.

And that is a perfectly valid stance to take, expressly because you recognize it is just a stance. Can Jaynes say the same?

So the only place I state my own perspective you don't have a problem with. Yet you should recognize that the previous quotes where pulled from a contextual set of assumptions in which the quotes only applied in that context. Wrt Jaynes I will articulate more when I get to the one point where I offered an opinion, you objected to, on how these context apply.

I'm not sure what you mean by a "physically defined world".

And here it is. When I used the term "physically defined world" it was not to specify a singular ontological perspective under which that term applied, as it could mean any of the perspectives previously described. It was merely to indicate that if by definition the world in which we interact with directly is a "physically defined world" then that definition imposes itself on how we can go about defining the physicality of the hurricane analogy, without changing any of the ontological perspectives concerning it. Hence to understand Jaynes position you merely have to accept this tradition definition simply because it defined so. Yet does not change any of the various ontological flavors under which differing people interpret it. Hence I meant it in the sense in which anybody might interpret it, and not just my own interpretation. In fact I stated a personal ambivalence toward which definition was best a priori, even under the context of the modeling symmetries you ignored and pulled quotes from out of context.

I have no problem with asserting that there is a territory to which the map refers, that's basic realism. My issue is with confusing attributes of the map with attributes of the territory. There is just no such thing as an attribute of a territory-- all attributes are attributes of a map.

Certainly confusing map attributes with the territory is a sticky problem. In a singular very limited context that is exactly what the PBR theorem attempted to address. Getting into personal opinion again here, but to say that the territory has no attributes (however primitive) to me entails that there are no derivative attributes or empirical data whatsoever. To me the notion of derivative properties without something from which they derive is just as magical as dynamical properties sprinkled on fundamental point particles. Of course that is my opinion just like the old magical dynamical properties in particle physics. Such a primitive foundational property may not even be empirically accessible in and of itself, though given as a postulate potentially entails empirically accessible properties. Denying such is at least possible is a form of the mind projection fallacy.

One of the complaints previously given about properties is the lack of a definition. Try this one on for size: A property is a constraint in the degrees of freedom of a set of variables or points in space. This would apply whether it was a purely mathematical constraint, or a simple purely mechanical constraint in which one part restrict the freedom of another. Makes no difference whatsoever, and such mechanical constraint is subject to mathematical laws. Yet how could you possibly have a Universe without constrained degrees of freedom, i.e., properties. Without such constraints every point would be causally disconnected and independent from every other point making observations impossible. Just like the unobservable independent variables Dr Chinese spoke of in Hume's[/PLAIN] Determinism Refuted.

 

[Fredrik]

Sure, but you were talking about two qubits, not one, and bringing them together.

PBR said something about bringing them together. I don't think I did. I hope I didn't, because I don't think such statements belong in a proof.

I have thought some more about my version of the "simplified" argument from page 2, and I'm now fairly certain that it's (essentially) correct. I'm too tired to explain all aspects of it now (especially the one detail that I'm still unsure of), so I'll just adress one that we've been discussing. The entanglement issue isn't an issue. It doesn't matter that unentangled states will remain unentangled, because the entangled states in the argument are post-measurement states, and a quantum theory isn't required to say anything about the measuring device (other than what operator it corresponds to). So the correct mental picture here is that there are no interactions in the quantum theory, but the measuring device can still entangle them.

Of course, the argument doesn't depend on mental pictures. There's no need to imagine "bringing them together", or to imagine anything at all. We don't need to know how to perform a measurement that has the results $|\xi_k\rangle$. It's sufficient to know that such an operator can be defined on $\mathcal H\otimes\mathcal H$.

 

[my_wan]

I have thought some more about my version of the "simplified" argument from page 2, and I'm now fairly certain that it's (essentially) correct. I'm too tired to explain all aspects of it now (especially the one detail that I'm still unsure of), so I'll just adress one that we've been discussing. The entanglement issue isn't an issue. It doesn't matter that unentangled states will remain unentangled, because the entangled states in the argument are post-measurement states, and a quantum theory isn't required to say anything about the measuring device (other than what operator it corresponds to). So the correct mental picture here is that there are no interactions in the quantum theory, but the measuring device can still entangle them.

(My bold)
This particular issue has worried me a bit. In fact the primary concern wrt the legitimacy of the theorem. However, to the best of my thinking this appears correct to me.

 

[Fredrik]

The part that's bothering me is the assumption or theorem (not 100% sure which) that the ontological model for the quantum theory of a single qubit can be used to define an ontological model for the two-qubit theory. I think this is a non-trivial point. I don't see how it can make sense to take it as an assumption, because we later find that it's not an ontological model of the two-qubit theory. That's the contradiction that's supposed to disprove our initial assumption, but now it looks like it may have been the result of another assumption.

So I think it must be proved as a theorem. It's not sufficient to show that there's some kind of model with state space $\Lambda\times\Lambda$. We also need to show that it makes the same predictions as the two-qubit theory. In other words, we need a theorem that shows that $if$ there's an ontological model with state space $\Lambda$ for a quantum theory with Hilbert space $\mathcal H$, then there's an ontological model with state space $\Lambda\times\Lambda$ for the quantum theory with Hilbert space $\mathcal H\otimes\mathcal H$. I think that this requires a pretty sophisticated argument, that comes with its own set of assumptions:

Physical justification for using the tensor product to describe two quantum systems as one joint system, by Diederik Aerts and Ingrid Daubechies.

 

[Ken G]

You pulled that quote out of the explicit context or assumptions under which it applied.

I wasn't saying you either did or did not agree with that conclusion, I was asking you if you did, and saying that I did agree with it-- I am fine with the idea that we hit bottom with no ontic entities anywhere, because I think that ontic entities are merely effective notions, not to be taken literally. Science has no need of a literal ontic entity, it works on effective and provisional ontic entities. It's just a fundamentally epistemological endeavor.

Hence for you to object solely within the narrow range of your own perspective is just as moot as my personal perspective was in the comparison.

Actually, I never objected at all, I merely said that among the alternatives you were considering, that is the one that I take as the correct position, in regard to how science works (rather than in regard to each person's individual assessment of the ramifications of science).

It was merely to indicate that if by definition the world in which we interact with directly is a "physically defined world" then that definition imposes itself on how we can go about defining the physicality of the hurricane analogy, without changing any of the ontological perspectives concerning it.

I still don't understand how you are using the term "physically defined world." We don't define the physicality of the hurricane analogy, we just define the hurricane, and its physicality is not something we get to define, it is something whose usefulness we test. And when we test it, we should expect it to be useful for some things, and break down for other things. So it is with ontic elements, we should never expect otherwise, and we certainly don't have the ability to define otherwise. The reason we can't define the physicality of a hurricane is because that is something we must test, we get to choose the definition of hurricane but not how well the concept will serve our physics.

The case of the atom is more immediate to the Jaynes issue. Jaynes claims that atoms are real, and that saying so is not an example of the mind projection fallacy. I claim it certainly is an example of just that. Neither of us can resort to definitions to support our cases, all we can do is define atom (and our definitions are the same), and see how the concept serves. We find it serves quite well, when it serves, and we find it is not very helpful when it does not serve.

For example, an ionized plasma may include atoms and particles in our description, but it also includes waves in fields and the combined effects of fields and atoms, sometimes called "dressed atoms." So is a dressed atom an atom, or isn't it? It's certainly not the same thing as an atom, that would simply be incorrect. Or we can go to more extreme environments, like a white dwarf star. The electrons in a white dwarf do not act like individual particles at all, they are so entangled with each other it would be closer to correct to imagine that the whole white dwarf is more like a single atom, than imagining it is comprised of independent particles. So is a white dwarf an atom, or isn't it? Surely if Jaynes is right, and atoms (and independent particles) are real, then we should be able to say if a white dwarf is a kind of atom, or if it is comprised of atoms. But we can't, the simplistic language fails us, because that's all it ever was-- simplistic language. The "atom" and "independent particle" concepts are just that-- epistemological constructs that we can get away with imagining are ontic in some situations, but not in others. I find Jaynes' characterizations of atoms to be surprisingly naive, he is projecting a simplifying concept onto reality in an overly narrow way. He is committing the mind projecton fallacy.

Certainly confusing map attributes with the territory is a sticky problem. In a singular very limited context that is exactly what the PBR theorem attempted to address. Getting into personal opinion again here, but to say that the territory has no attributes (however primitive) to me entails that there are no derivative attributes or empirical data whatsoever.

Derivative attributes and empirical data are whatever we make them. It's not one-or-the-other, that they either exist or have no value. That they have value is clear, but it does not make them real. In fact, this is just what we should expect.

One of the complaints previously given about properties is the lack of a definition. Try this one on for size: A property is a constraint in the degrees of freedom of a set of variables or points in space.

I don't think that solves the problem, because my issue was not that property was undefined, it was that the properties could determine what happens to the system. I don't think we can assume that what happens to a system is determined at all, at least not "determined" in the standard sense of "determinism." Where does this idea come from that behavior is determined? That's one of the most blatant examples of belief in magic, in my view.

Yet how could you possibly have a Universe without constrained degrees of freedom, i.e., properties.

That is exactly the question, yes. My answer is, "easy!" Indeed, I feel this should be our default assumption until otherwise demonstrated-- in the interest of basic skepticism.

Without such constraints every point would be causally disconnected and independent from every other point making observations impossible.

I feel that causal connection is a construct of how we think, just like properties. So I don't think we should imagine that its absence in some true ontology is a problem. Similarly, we should not conclude that some true ontology will include randomness-- we should be suspect of the entire notion of a true ontology.

 

[Ken G]

In other words, we need a theorem that shows that $if$ there's an ontological model with state space $\Lambda$ for a quantum theory with Hilbert space $\mathcal H$, then there's an ontological model with state space $\Lambda\times\Lambda$ for the quantum theory with Hilbert space $\mathcal H\otimes\mathcal H$. I think that this requires a pretty sophisticated argument, that comes with its own set of assumptions:

Physical justification for using the tensor product to describe two quantum systems as one joint system, by Diederik Aerts and Ingrid Daubechies.

Yes, I think that paper makes it quite clear the limitations of making that particular choice about how to treat two qubit systems. That's the formal version of what I was saying-- if the systems come together, the assumptions are not satisfied, and the tensor product approach simply isn't valid quantum mechanics. I'm not sure if PBR are assuming invalid quantum mechanics as a result, but this is certainly something we should be worried about.

 

[Fredrik]

if the systems come together, the assumptions are not satisfied, and the tensor product approach simply isn't valid quantum mechanics.

I still strongly disagree with this line of reasoning. You seem to be mixing bits of reality into a mathematical argument where they don't belong. I'm as confused by your persistence about this as I would have been if we had been discussing a proof of the theorem that says that there's no rational number x such that x²=2, and you go on for days and pages about how we have failed to account for gravity or something like that.

The fact that a theory of two non-interacting subsystems isn't going to make accurate predictions in certain real-world situations is irrelevant, because we're trying to prove a mathematical statement about the purely mathematical part of theory of just one of those subsystems, by using the rules that tell us how to combine several theories into one. These rules are also part of the framework of QM. These joint theories are just mathematical tools. We only use the purely mathematical parts of them. Real-world concerns don't enter into it.

 

[Demystifier]

A new paper on the PBR theorem:
http://xxx.lanl.gov/abs/1111.6304

 

[DevilsAvocado]

A new paper on the PBR theorem:
http://xxx.lanl.gov/abs/1111.6304

Thank you very much Demystifier.

I’m still reading this interesting paper, and already on the second page the essence of the PBR theorem is expressed very efficiently [my bolding]:

Very recently, Pusey, Barrett and Rudolph (PBR) have given a completely novel ‘no-go’ theorem [1], which demonstrates that, under certain assumptions, distinct pure quantum states must have disjoint sets of underlying properties. In particular, partially overlapping wave functions cannot be considered as partially overlapping ensembles of underlying properties, in any model that satisfies the PBR assumptions. Rather, the corresponding ensembles must be nonoverlapping, implying that the wave functions must be considered precisely just as ‘real’ or ‘physical’ as the underlying properties themselves.

The strength of the PBR theorem is determined by the strength of the assumptions it relies on.

Could someone explain what this means:

Further, it is shown that an assumption of measurement independence may be dropped to obtain a related result having the same experimental significance (at the expense of a weaker conceptual significance). The latter is a remarkable feature of the PBR approach, given that Bell inequalities, steering inequalities and Kochen-Specker theorems all require an assumption of this type.​

[Any philosophical mumbo-jumbo, if this discussion is for real or not, is preferably transferred to the proper forum]

 

[Ken G]

This is from the abstract of that new paper: "The `factorisability' assumption used by PBR is replaced by a far weaker `compatibility' assumption for uncorrelated quantum subsystems which, moreover, does not require the assignation of separate underlying properties to each subsystem (i.e, reductionism)." It sounds like Hall has addressed my main objection-- that PBR assumed that the systems had properties that determined the outcomes, and used that assumption to argue that "the wave functions must be considered precisely just as ‘real’ or ‘physical’ as the underlying properties themselves." That was the problem with PBR-- anyone who did not regard such properties as real or physical would have no reason to carry those attributes over to the states themselves, they could safely ignore the PBR proof. Perhaps this new proof avoids that problem, I haven't digested it yet.

 

[Ken G]

I still strongly disagree with this line of reasoning. You seem to be mixing bits of reality into a mathematical argument where they don't belong. I'm as confused by your persistence about this as I would have been if we had been discussing a proof of the theorem that says that there's no rational number x such that x²=2, and you go on for days and pages about how we have failed to account for gravity or something like that.

If one is claiming to prove something about states in quantum mechanics, one must apply the state concept from a version of quantum mechanics that is applicable and relevant, consistent with whatever situation one is using quantum mechanics to treat. If we were proving a theorem about classical mechanics, and did not include any gravity, someone could quite correctly point out that the theorem has not been proven for any situation involving both classical mechanics and gravity. That is what I am pointing out-- if the theorem assumes unentangled systems in the way the quantum mechanics is set up, then later proves something about how those systems are entangled, it is not proving anything about correct quantum mechanics, it is proving something about incorrect quantum mechanics. I'm not saying it really did that, for that would make the proof wrong, I'm saying that's why you have to worry about assuming unentangled systems but then later bringing the systems together, which seemed to be what you were doing.

The fact that a theory of two non-interacting subsystems isn't going to make accurate predictions in certain real-world situations is irrelevant, because we're trying to prove a mathematical statement about the purely mathematical part of theory of just one of those subsystems, by using the rules that tell us how to combine several theories into one. These rules are also part of the framework of QM.

The first rule about how to combine theories of non-interacting subsystems is that the non-interacting subsystems had better never be brought together, so no questions about their entanglement had better be of interest in the proof. It's not an issue of real-world concerns, it is purely an issue of internal consistency of the treatment chosen.

 

[JK423]

OK, new summary. Simplified.

They are comparing two different schools of thought:

1. A state vector represents the properties of the system.
2. A state vector represents the statistical properties of an ensemble of identically prepared systems, and does not also represent the properties of a single system.

Their argument against the second view goes roughly like this:

Suppose that there's a theory that's at least as good as QM, in which a mathematical object λ represents all the properties of the system. Suppose that view 2 above is the correct one. Then λ doesn't determine the probabilities of all possible results of measurements. Yada-yada-yada. Contradiction! Therefore view 2 is false.​

I say that

• The entire article rests on the validity on the statement in brown, which says that view 2 somehow implies that "all the properties" are insufficient to determine the probabilities. (If that's true, then why would anyone call them "all the properties"?)
• The brown statement is a non sequitur. (A conclusion that doesn't follow from the premise).
• The only argument the article offers in support of the brown claim, doesn't support the brown claim at all.

Am I wrong about something?

Fredrik,
I had the same questions during my first reading of the paper. I think that i have understood what the authors are trying to say, so let's see if my understanding is correct. Let me note that i haven't read all the replies that you've got from other people, so excuse me if i repeat arguments someone else has already said!

I think that the key ingredient is to understand what the authors mean by 'Statistical interpretation' and what by the 'physical properties {λ}'.

1] Statistical interpretation according to the authors
In the abstract of the paper we read:
"Another (view) is that even a pure state has only a statistical significance, akin to a probability distribution in statistical mechanics"
Which means that they regard as the statistical interpretation of the state vector the same thing as a probability distribution in statistical mechanics.
But what happens in the classical case?
Lets assume that we got two ensembles of (classical) ideal gases, ensembles 1 & 2, in the same volume of space but in different temperatures. These ensembles do not interact (ideal).
Each ensemble ( i ) will be described by the Mawell-Boltzmann probability distribution that goes like P$_{i}$$\propto$exp(-E$_{i}$/kT$_{i}$).
The energy levels E$_{i}$ are the same for both gases, only the probabilities change. Now, we measure a random particle in the volume -without knowing beforehand in which of the two ensembles it belongs- and we get it's position and its momentum (even its trajectory!) which constitute its set of physical properties {λ}. But knowing {λ} in the classical case allows us to also know in which ensemble the particle belongs? Or in other words, by which probability distribution P$_{i}$$\propto$exp(-E$_{i}$/kT$_{i}$) it's described?
The answer is no.
According to the authors, this is the fact that makes a classical distribution not a physical property of a classical system, but its only of statistical nature.
So, repeating this essential -to my opinion- point, in the classical case even if knowing all the physical properties {λ} of the system we still cannot distinguish the ensemble that this system belongs IF this ensemble's probability distribution overlaps with other ensemble's probability distribution to the physical properties {λ} that they assign probabilities to.


2] Physical properties {λ}
In classical physics, this set {λ} consists of things like position, momentum, energy, etc
But what does {λ} mean to quantum mechanics?
To my mind, there are 2 possibilities:
- The first is that {λ} represent all the good quantum numbers of the state vector. So Knowing {λ} you can immediately know the state vector. Ofcourse we assume the Schrodinger equation (or a better undiscovered equation) to hold. Let's give an example. If our particle is a potential V(x), then it has a specific energy spectrum and by solving the 'S' equation we can find all the eigenkets of the Hamiltonian. If energy is a good quantum number, then knowing 'E' (energy) allows us also to know the state vector of the particle. So in this simple case, the set {λ} consists of the energy E.
- The above would be okay if the particle's state has good quantum numbers. If it hasnt (is there a physical state without no good quantum numbers??) then the only option that comes to my mind (instead of saying {λ}=0 ) is that there is another undiscovered theory that gives us a set {λ}. If you can think of something better please tell me.

Let's hit the problem now, and repeat the argument of the authors (quote from Fredrik):
<<Suppose that there's a theory that's at least as good as QM, in which a mathematical object λ represents all the properties of the system. Suppose that view 2 (statistical) above is the correct one. Then λ doesn't determine the probabilities of all possible results of measurements. Yada-yada-yada. Contradiction! Therefore view 2 is false>>

I think that now it's clear what the authors mean. If the state vector is of statistical nature as is a classical probability distribution, then -according to what we said above about the classical distributions- even if we know the whole set of physical properties {λ}, we will still not be able to determine the state vector (aka the probabilities of all possible results of measurements).


Tell me your thoughts.



John

 

[bohm2]

A new paper on the PBR theorem: http://xxx.lanl.gov/abs/1111.6304

I'm still trying to understand the last paper but here's a quoted comment from Matt Leifer posted regarding this newest Hall paper:

As far as I can see, this paper is a fairly straightforward extension of PBR, but I only think that one of the weakened constraints is conceptually interesting. The original proof required a factorizability condition, i.e. for product states you have a Cartesian product of ontic state spaces and the distribution is independent over the factors. This can be replaced by a “local compatibility” condition, which is just the condition that if lambda is a possible ontic state for a single copy of a bunch of different states, then n copies of lambda is possible for any tensor product of n states chosen from that set. This drops the independence part of the assumption. Why this is true is very easy to see, since this is the only property of factorizability used in the original PBR result.

Hall also claims to have weakened this further to a condition of “compatibility”. This is supposed to go beyond reductionist models, which say that each system has its own individual ontic properties and the properties of composite systems are simply the collection of properties of all the parts. Hall tries to go beyond this by allowing the ontic state space of two systems to be arbitrarily different from the cartesian product of the ontic state spaces of the individual systems. I don’t think this has been achieved, since one still needs to know how the properties of the global system are related to the properties of the subsystems. Hall says that if we know that lambda is compatible with some states of one system, then we need only know that lambda is compatible with n-fold products of those states. However, since the state spaces are completely distinct, I don’t think that it makes sense to consider lambda as a possible ontic state for both a subsystem and the full composite system. This is not the case in the original theorem, or in the version with local compatibility, in which case the state on the global system is n copies of lambda rather than just one. Therefore, I don’t think that this part of the paper makes much sense.

Hall also points out that the probability distribution over the ontic state need not be independent of the choice of measurement, since only one measurement is considered for each pair of states. Whilst this is true, and perhaps interesting because it places a constraint on certain types of retrocausal theory, it does not allow the original PBR conclusion to be drawn. If another choice of measurement were made then the distributions could overlap and the quantum state would be epistemic. It is this loophole that I hope to exploit in developing an epistemic retrocausal theory. Perhaps this is worth saying, but it is certainly not groundbreaking.

http://www.scottaaronson.com/blog/?p=822

 

[Ken G]

I found this insight in that Leifer quote to be telling: "This is supposed to go beyond reductionist models, which say that each system has its own individual ontic properties and the properties of composite systems are simply the collection of properties of all the parts. Hall tries to go beyond this by allowing the ontic state space of two systems to be arbitrarily different from the cartesian product of the ontic state spaces of the individual systems. I don’t think this has been achieved, since one still needs to know how the properties of the global system are related to the properties of the subsystems." I think this quote makes it clear that Leifer views the algebra of "properties" to be an essential aspect of the PBR theorem, and he feels that the Hall modification does little to relax that. By "algebra of properties", I mean simply the way the concept of properties proliferates throughout the logic of the proof such that they allow us to draw conclusions about how composite systems can be treated in quantum mechanics, but these choices limit the validity to a version of quantum mechanics that supports the concept of properties-- which is very close to circular reasoning in the proof. Thus I continue to feel that the most important conclusions based on the proof are upheld only in a circular interpretation of the proof, and this limitation is apparently not much improved in the Hall modification.

 

[Fredrik]

If one is claiming to prove something about states in quantum mechanics, one must apply the state concept from a version of quantum mechanics that is applicable and relevant, consistent with whatever situation one is using quantum mechanics to treat.

You're already mixing in bits of reality where they don't belong. We're not "treating" anything, so terms like "applicable" don't make sense. We're talking about a mathematical property of a quantum theory with a 2-dimensional Hilbert space, and the standard procedure to define new theories from old ones.

If we were proving a theorem about classical mechanics, and did not include any gravity, someone could quite correctly point out that the theorem has not been proven for any situation involving both classical mechanics and gravity. That is what I am pointing out--

But what we're talking about (the page 2 argument, and my version of it from post #155) is nothing like that. A better analogy would be a theorem that says that in the classical theory of a single point particle in Galilean spacetime moving under the influence of no force at all, the world line is always a straight line.

 

[Fredrik]

I think that the key ingredient is to understand what the authors mean by 'Statistical interpretation' and what by the 'physical properties {λ}'.

Knowing what they mean by statistical interpretation is crucial. They are using the definitions of Harrigan & Spekkens. To them "a state vector can be interpreted statistically" means "there's a ψ-epistemic ontological model for this quantum theory".

I don't think the exact meaning of "properties" really matters here. It certainly plays no role in the mathematical part of the argument, since the term doesn't have a mathematical definition. Mathematically, λ is just a member of a set in another theory, one that makes the same predictions as QM. (In this theory, the probability of a result k of a measurement M is determined by λ,k and M).

Let's hit the problem now, and repeat the argument of the authors (quote from Fredrik):
<<Suppose that there's a theory that's at least as good as QM, in which a mathematical object λ represents all the properties of the system. Suppose that view 2 (statistical) above is the correct one. Then λ doesn't determine the probabilities of all possible results of measurements. Yada-yada-yada. Contradiction! Therefore view 2 is false>>

When I wrote this, I thought they were saying that "if view 2 is correct, then λ doesn't determine the probability distribution". They are actually defining view 2 as "there's an ontological model such that λ doesn't determine the probability distribution". So that particular bit of criticism was unfair.

I think that now it's clear what the authors mean. If the state vector is of statistical nature as is a classical probability distribution, then -according to what we said above about the classical distributions- even if we know the whole set of physical properties {λ}, we will still not be able to determine the state vector (aka the probabilities of all possible results of measurements).

Yes, I'd say that this is what they mean by statistical view, but the statement can be made more precise using the definitions of Harrigan & Spekkens. The statistical view (as they define it) is that every quantum theory has a ψ-epistemic ontological model.

 

[DevilsAvocado]

... That was the problem with PBR-- anyone who did not regard such properties as real or physical would have no reason to carry those attributes over to the states themselves, they could safely ignore the PBR proof. Perhaps this new proof avoids that problem, I haven't digested it yet.

I don’t think this is a problem related to PBR, but a total lack of understanding somewhere else.

It should be pretty obvious that those advocating a ψ-epistemic ontological model obviously regard such underlying properties as real.

 

[apeiron]

Hall tries to go beyond this by allowing the ontic state space of two systems to be arbitrarily different from the cartesian product of the ontic state spaces of the individual systems. I don’t think this has been achieved, since one still needs to know how the properties of the global system are related to the properties of the subsystems.

I thought My Wan's earlier comment is insightful here:

A property is a constraint in the degrees of freedom of a set of variables or points in space.

This is the non-reductionist or contextual view in a nutshell. What you find locally is what's left still to be free after global constraints have limited the freedoms that might otherwise have existed.

So wavefunction entanglement becomes not about the mixing of properties but the merging of constraints. Merged constraints are a relaxation which in turn makes the "properties" less definite. Collapse of the wavefunction is the tightening of constraints again to produce more definite "properties" once more.

Reductionism tries to build its model of the world atomistically from the bottom-up. Which leads to the view that the wavefunction must be some kind of extended object - a definite thing with its own location, existence and properties.

But the other way of looking at it is that the wavefunction is just our description of the constraints as they stand in reference to some location. It stands for the information that impinges to limit what exists. Entanglement then reduces the amount of information, creating increased uncertainty/more freedom.

A wavefunction could thus be ontic, but not in the sense of an object. Just as actually a set of constraints.

 

[DevilsAvocado]

... Personally, I operate on the presumption that it is not turtles all the way down, that there exist an ontic building blocks of some sort (likely transfinite) lacking any properties other than existing, where all properties are emergent constructs analogous to the way the hurricane is an emergent property. And I remain ambivalent toward the choice of definition as to whether a hurricane in itself is ontic or epistemic. It is merely a partitioned set of properties of a property set which are not more generally partitioned or partitionable in such a manner.

my_wan, I promised a 'voluminous' reply... but I realized this thread is rapidly going down the derailed track without my 'professional help'... ;) therefore; I rest my case.

I respect your ideas, and your way of debating – it’s sincere. But I’m afraid that your buddy is as far from your position one could come, and the quote above shows this clearly.

Ken G is advocating Idealism (when not beating around the bush), i.e. reality is fundamentally mentally constructed and a skepticism about the possibility of knowing any mind-independent thing, i.e. diametrically your position.

"So that is the sense that I am saying there is a crucial role of consciousness in quantum mechanics-- there simply is no such thing as quantum mechanics without it."​

And sometimes "quantum mechanics" is everything there is, the whole world and the universe. And sometimes it’s "quantum mechanics" in the microscopic world. And sometimes it’s the theory of quantum mechanics. And sometimes he replaces "quantum mechanics" for "physics", and then he picks and chooses as it fits...

= Impossible to debate

jfyi

 

[my_wan]

I wasn't saying you either did or did not agree with that conclusion, I was asking you if you did, and saying that I did agree with it-- I am fine with the idea that we hit bottom with no ontic entities anywhere, because I think that ontic entities are merely effective notions, not to be taken literally. Science has no need of a literal ontic entity, it works on effective and provisional ontic entities. It's just a fundamentally epistemological endeavor.

I see now that I was overly narrow in my interpretation your response. Though I often add some indication of my personal views, as a side note in such post, the main point is more often the range or space of possibilities neglected under any given opinion or characterization. For instance, when you say "ontic realism as a kind of useful fantasy" my take on this is that we do not know and often cannot know even in principle, what constitutes a "useful fantasy" verses an actual state. Hence to a priori label any of these foundational positions as a "fantasy" itself goes beyond what we can know. Certainly in some cases we know we are working with a "useful fantasy", but to say that because we are fundamentally limited in our capacity to "know" entails that all such characterizations are factually "useful fantasies" tacitly oversteps what we can factually know, such a claim is a mind projection fallacy. So I don't a priori reject alternative characterizations unless I can show it runs afoul of valid consequences, whether that be internal self consistency or empirical validity or both.

Wrt your question about my opinion specifically, I do not see that as a a perfectly natural conclusion. To fully justify that would require subverting this thread to an unwarranted degree, as it would require centering the debate solely around a personal view. However, in my opinion such a conclusion appears just as magical to me as the claim that fundamental point particles are real with magical properties sprinkled on like raisins. To some realist your opinion as stated does not even constitute realism. The same issues involving what constitutes realism is at the heart of why I used "physically defined world" in such an inclusive manner.

Actually, I never objected at all, I merely said that among the alternatives you were considering, that is the one that I take as the correct position, in regard to how science works (rather than in regard to each person's individual assessment of the ramifications of science).

Yes, my apologies. I recognize that the narrowness in which I interpreted your response was unwarranted, but it was formulated from your own singular opinion. I was explicitly trying to consider the space of all such opinions without a priori judging anyone opinion solely on the basis of of any other singular opinion.

I still don't understand how you are using the term "physically defined world." We don't define the physicality of the hurricane analogy, we just define the hurricane, and its physicality is not something we get to define, it is something whose usefulness we test. And when we test it, we should expect it to be useful for some things, and break down for other things. So it is with ontic elements, we should never expect otherwise, and we certainly don't have the ability to define otherwise. The reason we can't define the physicality of a hurricane is because that is something we must test, we get to choose the definition of hurricane but not how well the concept will serve our physics.

Some people describe "physical" purely in terms of ontic entities in a sense that hurricanes are not fundamentally a separable "physical" entity. To either this group or the group of opinions which do not define or label the world we live in as a physical world the term I provided does not apply. However, any group of opinions which defines or labels the world we live in a physical world, whether that includes ontic foundations or not, then that entails the same label to be associated irrespective of the foundational opinions used to define it. In other words it makes no sense to define the world in which we directly interact "the physical world" while also denying that the actual constituents from which the world is derived are not physical. Like denying atoms are not real, but hurricanes are. In a sense that is trying to have your cake and eat it to. So I'm not objecting to either an ontic or epistemic foundational characterization. I'm simple saying that if you label it one way at the experiential level then denying those same labels at a different level is incongruent.

For instance, I do do not object to you calling yourself a realist even though you do not attach the "real" part of [real]ist to the real existence of any ontic entities. Yet to many realist this is like saying: I'm a realist because I don't believe the Universe consist of any real ontic entities. You can object that real is not exclusive of things other than ontic entities, but neither is "physical" in "physically defined world".

The case of the atom is more immediate to the Jaynes issue. Jaynes claims that atoms are real, and that saying so is not an example of the mind projection fallacy. I claim it certainly is an example of just that. Neither of us can resort to definitions to support our cases, all we can do is define atom (and our definitions are the same), and see how the concept serves. We find it serves quite well, when it serves, and we find it is not very helpful when it does not serve.

Jaynes wrote the mind projection fallacy in far more detail than what can be accurately summed up with that one statement. For instance, you state the opinion that it is natural that real ontic entities are not the foundational basis of the universe. If I applied you judgement of Jaynes to this statement couldn't I insist that you are not a realist, and that calling yourself so constitutes a mind projection fallacy ostensibly to justify the [real]ity of your own opinion?

For example, an ionized plasma may include atoms and particles in our description, but it also includes waves in fields and the combined effects of fields and atoms, sometimes called "dressed atoms." So is a dressed atom an atom, or isn't it? It's certainly not the same thing as an atom, that would simply be incorrect. Or we can go to more extreme environments, like a white dwarf star. The electrons in a white dwarf do not act like individual particles at all, they are so entangled with each other it would be closer to correct to imagine that the whole white dwarf is more like a single atom, than imagining it is comprised of independent particles. So is a white dwarf an atom, or isn't it?

How does this differ from the hurricane analogy? It certainly does not make sense to talk about the wind shear forces in some region of the hurricane as independent variables from other regions. Hence without dressing the atoms such that the hurricane is structurally dependent on the whole distribution of atoms it is simply, in your words incorrect. Thus you have added absolutely nothing to the hurricane analogy with "dressed atoms" or group behavior (as though a single entity). You merely chose a more complex yet equivalent analogy. The hurricane is in fact

Surely if Jaynes is right, and atoms (and independent particles) are real, then we should be able to say if a white dwarf is a kind of atom, or if it is comprised of atoms. But we can't, the simplistic language fails us, because that's all it ever was-- simplistic language. The "atom" and "independent particle" concepts are just that-- epistemological constructs that we can get away with imagining are ontic in some situations, but not in others. I find Jaynes' characterizations of atoms to be surprisingly naive, he is projecting a simplifying concept onto reality in an overly narrow way. He is committing the mind projecton fallacy.

First off to say atoms are real does not entail that they are strictly independent, any more than a real hurricane is independent from the atmosphere, a white dwarf star is not independent of the mass it contains, etc. The hurricane maintains its existence as the result of the entanglement between its parts, and to get this entanglement requires nothing more than the fact that the (independent) parts cannot occupy the same space. Hence saying we should be able to tell if a white dwarf is a kind of atom is like saying if pool balls are real independent entities we should be able to say if pool balls are a type of triangle because they form a triangle in the raked position. The hurricane analogy was intended to make this lack of independence obvious, like your "dressed atoms", even when the molecules themselves are considered as independent entities. Though I relaxed this assumption that atoms are independent entities after the fact, not because of the hurricane superstructure but because they could have interdependent substructures of their own like the hurricane.

Derivative attributes and empirical data are whatever we make them. It's not one-or-the-other, that they either exist or have no value. That they have value is clear, but it does not make them real. In fact, this is just what we should expect.

No, we cannot make derivative attributes or empirical data what we want. They have a certain symmetry and we can represent these symmetries in whatever way we want. But only so long as that symmetry is strictly maintained. Under no circumstances can we describe it as a different symmetry without being invalid, period. That is why symmetries take center stage in modern physics. It's the only thing we can both know and is not subject to choice, such as ontological opinions are. It is also what makes theorems, such as PBR, possible and meaningful in constraining possible models or interpretations of QM.

I don't think that solves the problem, because my issue was not that property was undefined, it was that the properties could determine what happens to the system. I don't think we can assume that what happens to a system is determined at all, at least not "determined" in the standard sense of "determinism." Where does this idea come from that behavior is determined? That's one of the most blatant examples of belief in magic, in my view.

Though you are right that we cannot assume a priori determinism determines what happens in the usual sense, neither can we assume it doesn't in spite of contrary opinions. Doing so is a fallacy: We cannot assume X therefore not X, is a version of if we cannot know X therefore not X, is a version of if we cannot observe X therefore X does not exist. In the most general sense "determines" the properties could entail the determination of properties that are not deterministic, such as common interpretations of QM statistics.

That is exactly the question, yes. My answer is, "easy!" Indeed, I feel this should be our default assumption until otherwise demonstrated-- in the interest of basic skepticism.

I certainly have my own set of default assumptions. However, by designating some assumptions as default in general becomes a limiting factor in how we progress. Many non-realist attempt to characterize their assumptions as the only valid default assumption on the grounds of EPR and less often other no-go theorems. Thus attempting to invalidate research into various forms of contextualized variables. This is no more or less valid than realist making claims about how reality must be. So I do not hold that science or its practitioners should be held to standards of default assumptions, in the interest of exploring the space of possibilities. Just don't grandstand claims of how uniquely valid a particular set of default assumptions is in "reality".

I feel that causal connection is a construct of how we think, just like properties. So I don't think we should imagine that its absence in some true ontology is a problem. Similarly, we should not conclude that some true ontology will include randomness-- we should be suspect of the entire notion of a true ontology.

How we codify causal connections in science almost certainly is a construct of how we think. Yet the symmetries these causal connections entail are not. that is how and why we can formulate perfectly valid no-go theorems like PBR and still argue over the context it applies. Even if you had a perfectly valid model that was so strongly classical it would have made many of Newtons critiques happy, the range of interpretations at the experiential level would not diminish. However, the symmetries would impose constraints such that any valid interpretation of emergent or derivative constructs could in principle be mapped liked a coordinate transform. If one model gives property set A and another equally valid model gives property set B, then set A can be mapped onto set B and visa versa, else the two models would not be equally valid.

I think that you appear to be undervaluing the immutability of symmetries on the grounds that these symmetries can be contextualized in a myriad of different ways. In it's simplest form the true reality that some people chase is equivalent to arguing over whether the car was doing 70 mph or the ground was doing 70 mph under it. In more complex circumstances this non-physical coordinate attribute vastly changes the character and even apparent identity of what reality is. Even your "dressed atoms" is simply a regrouping of coordinates such that variable sets are regrouped as fewer sets of different variables. It doesn't invalidate the independent variables, made dependent through their interactions, it simply makes the problem more tractable by throwing away the details (large numbers of variables) not needed to characterize the system.

 

[my_wan]

my_wan, I promised a 'voluminous' reply... but I realized this thread is rapidly going down the derailed track without my 'professional help'... ;) therefore; I rest my case.

I respect your ideas, and your way of debating – it’s sincere. But I’m afraid that your buddy is as far from your position one could come, and the quote above shows this clearly.

Ken G is advocating Idealism (when not beating around the bush), i.e. reality is fundamentally mentally constructed and a skepticism about the possibility of knowing any mind-independent thing, i.e. diametrically your position.

"So that is the sense that I am saying there is a crucial role of consciousness in quantum mechanics-- there simply is no such thing as quantum mechanics without it."​

And sometimes "quantum mechanics" is everything there is, the whole world and the universe. And sometimes it’s "quantum mechanics" in the microscopic world. And sometimes it’s the theory of quantum mechanics. And sometimes he replaces "quantum mechanics" for "physics", and then he picks and chooses as it fits...

= Impossible to debate

jfyi

Yes, I really should let this go since it appears that no matter how I try to keep it with the space of possibilities it still keeps being dragged back down to the personal perspective level.

 

[Ken G]

Ken G is advocating Idealism (when not beating around the bush), i.e. reality is fundamentally mentally constructed and a skepticism about the possibility of knowing any mind-independent thing, i.e. diametrically your position.

No. Once again you have failed to understand my point! Idealism is quite different from what I'm advocating, I'm actually advocating something more along the lines of "scientifically consistent realism." The difference between idealism and realism is simple-- idealism asserts that reality is fundamentally mind-constructed, so there is no reality outside the mind. This would also require I speak of my mind, because if there is no reality outside my mind, then your mind does not exist outside of my mind. I've never said any such thing, just look.

Indeed, scientists often find it useful to adopt realism, and I am no exception. Realism asserts that there is a reality outside our minds, and our minds are trying to figure it out. This is the stance I take. But here we must distinguish two brands of realism, which I would call "naive realism" (the idea that when we conceptualize reality, we hit it spot on, in complete contradiction with both the obvious limitations of our senses and our intelligence, and ignoring the clear evidence to the contrary from the history of our own physics), versus what I would call "scientifically consistent realism" (a realism that does not disregard that evidence).

So what am I actually saying? First of all, it's a bad idea to get my ideas interpreted through DevilsAvocado, because he always needs to replace them with something different so he can find some oversimplified objection to them. What I am actually saying is that given that physics changes all the time, and given that we only have our intelligence, historical experience, technology, and five senses to draw upon, the way we conceptualize reality is always going to be different from actual reality. Scientifically speaking, "reality" is the former, not the latter-- it is what we can say about reality, what our physics reveals about reality, but we have no coherent language for even talking about reality as it truly is. So there are no "true" ontologies in physics, there is just what we choose to regard as true, along with the reasons we choose to do that. These choices are contextual and provisional, and can vary in the same paragraph as we describe some physical phenomenon. This is as it should be-- we never had any other scientific relationship with reality, and we should not pretend we ever did or ever will. We simply confuse our own goals when we don't recognize what scientific realism actually is.

"So that is the sense that I am saying there is a crucial role of consciousness in quantum mechanics-- there simply is no such thing as quantum mechanics without it."​

Yes, that is what I am saying, but note there is nothing in that statement that represents idealism. All there is is the recognition of what quantum mechanics is, and the demonstrable fact that quantum mechanics is our attempt (one of many) to understand reality.

And sometimes "quantum mechanics" is everything there is, the whole world and the universe.

Again, your "interpretations" border on the ridiculous. All may be well assured that every time I say "quantum mechanics", I mean just one thing: the theory of quantum mechanics, like you can find in any textbook. I can't even imagine why anyone else would use the term to mean anything different.

 

[DevilsAvocado]

Again, your "interpretations" border on the ridiculous. All may be well assured that every time I say "quantum mechanics", I mean just one thing: the theory of quantum mechanics, like you can find in any textbook. I can't even imagine why anyone else would use the term to mean anything different.

Well, you tell me. The fact is that this is exactly what you do, from the thread "Quantum Eraser and Its Implications":

I'm pointing out that the fundamental weirdnesses associated with two-slit experiments are fundamentally about the role of the consciousness, for the simple reason that only a conscious being can perceive a nonunitary outcome.

This is not theory, this is an empirical experiment, and as usual "your consciousness" plays a fundamental role in this. I leave it to the reader to decide what’s ridiculous or not.

So what am I actually saying?

That’s what we are all wondering.

It seems like contradictions. Fredrik & my_wan has spent numerous posts on you, trying to sort things out, without success.

I hope you don’t blame me for this failure as well.

 

[Ken G]

Certainly in some cases we know we are working with a "useful fantasy", but to say that because we are fundamentally limited in our capacity to "know" entails that all such characterizations are factually "useful fantasies" tacitly oversteps what we can factually know, such a claim is a mind projection fallacy.

How can you tell in which cases we are working with a "useful fantasy" about the reality and which cases we are working with the actual reality? To even make this language internally inconsistent, we must accept that even fantasies have a sliding scale of connection to reality, which is just what I mean by "usefulness", but never cross a line into being something fundamentally different from a fantasy-- all that demonstrably changes is the usefulness of the fantasy. Yes, in standard language, we don't call something a fantasy any more if it has demonstrable usefulness, but this is sheer convenience-- we do not need to lose sight of the fact that the same basic process occurs with a useful fantasy and a pure fantasy, they are both mental pictures we adopt to achieve some purpose. All that changes is the purpose, and the standard of usefulness that is applied. My use of the term "fantasy" is not designed to suggest that science is pure fantasy, it is designed to place scientific thinking into its demonstrably proper place: inside our head, where it quite clearly does indeed occur.

To some realist your opinion as stated does not even constitute realism.

Indeed, and this is the central point. I'm not trying to divert this thread into a discussion of my personal philosophical opinions, this issue is right at the heart of just exactly what it is that PBR has proved about valid interpretations of quantum mechanics. PBR have adopted a very narrow view of what realism is, too narrow to be able to claim that they are using "only mild assumptions." Their version of realism is indeed often adopted by scientists, but I claim that it is internally inconsistent with science.

Now, I will admit that it is typical for scientists to adopt a view of scientific ontology that is perfectly convenient but rather naive, and is not really consistent with either the historical trajectory of science, nor to what scientists actually do. In particular, nothing in the history of physics, nor in the actions of any physicist, actually require any such thing as a concept of a true physical ontology (including the concept of "properties" that drive the logic of the PBR argument). In history, and in practice, all physical ontologies are borrowed from mathematics, and have no formal status within physics itself. They are contextual, provisional, and goal-oriented, a fact that is perfectly demonstrable by considering any standard physics curriculum. Thus, there is no basis for claiming that "realism" involves regarding physics as something that it has never been and likely never will be. None of this has anything to do with my personal philosophical choices, it is all just demonstrable truths about what physics is, not what we might like it to be. So I am arguing that the "realism" that PBR regards as a "mild assumption" in their proof is not only highly unrealistic, it is an example of the mind projection fallacy. Or should I say, the mind projection fantasy!

In other words it makes no sense to define the world in which we directly interact "the physical world" while also denying that the actual constituents from which the world is derived are not physical. Like denying atoms are not real, but hurricanes are. In a sense that is trying to have your cake and eat it to. So I'm not objecting to either an ontic or epistemic foundational characterization. I'm simple saying that if you label it one way at the experiential level then denying those same labels at a different level is incongruent.

And I would say the simple path that avoids any such incongruences is simply recognizing that any ontological statements we choose to make, whether they be about hurricanes or atoms or any physical "properties" of our world, are all going to be effective and useful pictures that we are choosing to borrow from conceptual structures like mathematics or everyday experience, and have no separate "existence" in the real world-- they exist only in the conceptual structures that we borrow them from. Same for properties-- so we can use properties within the context that they serve us, but we cannot prove things from using them, we cannot let a picture drive our logic that tells us what kinds of interpretations of quantum mechanics are possible, unless we allow that our proof only applies to those who would enter into our picture, and make our "mild" assumptions.

For instance, you state the opinion that it is natural that real ontic entities are not the foundational basis of the universe. If I applied you judgement of Jaynes to this statement couldn't I insist that you are not a realist, and that calling yourself so constitutes a mind projection fallacy ostensibly to justify the [real]ity of your own opinion?

The issue here is, which should we regard as the "null hypothesis": that the ontic entities we create in our language about reality really are the foundational basis of the universe, or that they really are only what we can demonstrate them to be (ideas we create in our language and our mathematical theories, which are then transplanted from the conceptual structures in which they demonstrably exist and used in physical contexts where they do not demonstrably exist). All I am saying is this: the true realist must adopt the latter, not the former, as their null hypothesis, because to do otherwise is a basic category error. It is fully realistic to notice category errors, that's not a mind projection fallacy. Ironically, the mind projection fallacy is an identification of a particular type of category error, and I claim that my approach is the one that avoids mind projection fallacies.

How does this differ from the hurricane analogy?

It doesn't, it's just another such analogy taken from physics. The hurricane analogy serves admirably, it is a perfect example of what I mean when I say that scientific ontologies are contextual, provisional, and goal-oriented, and that is also the reason that if we wish to imagine that systems have "properties", we should not use that picture to drive a logical necessity that these properties must determine the behavior of the system. That is actually reverse logic-- the usefulness of properties stems solely from the behaviors of the systems, not the other way around, and the usefulness of the property concept is contextual, provisional, and goal-oriented, but not unique and not logically closed. It should never appear in any proof of anything general, and it should never be viewed as a "mild" assumption, but rather, it is the assumption that colors everything that results from it. Not recognizing the import of what has been assumed is always the source of circular reasoning.

First off to say atoms are real does not entail that they are strictly independent, any more than a real hurricane is independent from the atmosphere, a white dwarf star is not independent of the mass it contains, etc.

True, but if atoms are real, and dependent on other things for that reality, then we must also assert what those other things are or else we cannot coherently talk about what an atom is. Again, the escape from this paradox is simple-- there is no need at all to regard atoms, or hurricanes, as real, so we can talk about them the way we should be talking about them: as concepts and pictures that we evoke for some specific and contextual purpose. That's just exactly what they are, why on Earth should we need to pretend they are something different to be able to call ourselves realists? Why do we need to be unrealistic to count ourselves realists? I say the realist is the person who does not fool themself.

Hence saying we should be able to tell if a white dwarf is a kind of atom is like saying if pool balls are real independent entities we should be able to say if pool balls are a type of triangle because they form a triangle in the raked position.

Yes, that's right, that's the problem with true ontologies! They just don't lead to coherent and internally consistent language, that's why it is a fantasy to imagine that a pool ball is a real thing, and not what it quite demonstrably is: a picture we borrow from some conceptual structure (generally geometrical or mathematical in nature) because it serves various purposes for us to so borrow it. But serving some purposes does not require it serve all purposes, whereas if a pool ball was "really real", then it must serve all purposes. How can something be real but break down in some context? For example, if a pool ball is real, does it have a surface, or doesn't it? Is the pool ball real, but its surface is not real? You can see the dilemmas one gets into if one insists on making the mind projection fallacy that objects that have demonstrable existence only in some conceptual structure also have existence in the "real world."

That is why symmetries take center stage in modern physics. It's the only thing we can both know and is not subject to choice, such as ontological opinions are. It is also what makes theorems, such as PBR, possible and meaningful in constraining possible models or interpretations of QM.

Yet the stated assumptions of PBR are not "let us assume the following symmetry." Instead, their assumption was that systems have properties that determine what happens to the system. Nothing in physics requires this to be true, and nothing in realism requires it either, unless a naive version of both is in use.

Though you are right that we cannot assume a priori determinism determines what happens in the usual sense, neither can we assume it doesn't in spite of contrary opinions.

Nothing in my logic requires that determinism is wrong, just like nothing in the mind projection fallacy requires that what the mind is projecting is wrong. It only requires that it is not known to be right, and thinking it must be right is then the fallacy-- the same fallacy applied by the PBR assumptions.

How we codify causal connections in science almost certainly is a construct of how we think. Yet the symmetries these causal connections entail are not.

I would label that as a mind projection fantasy-- the idea that we can tell the difference between when our codifications are a construct of how we think, and when they are not. We just don't have that ability, it's logically impossible. Symmetries also come from our mind, they are concepts that demonstrably exist in a mathematical or geometrical structure only. Applying them in the real world is just as contextual, provisional, and goal-oriented as any other scientific ontology, and thinking they are something "more real" than that is a mind projection fallacy.

If one model gives property set A and another equally valid model gives property set B, then set A can be mapped onto set B and visa versa, else the two models would not be equally valid.

I agree with that but I'm not sure I see the relevance-- models are always going to invoke properties, that's just what they do. But the models never cause reality to do what the model does, so there is never any reason to imagine that the reality involves "hidden variables" that are not in the model. If the properties are not in the model, they are not "hidden", they are simply nonexistent for that model (and reality never has them). We can imagine some other model that does use those properties, but we cannot say those properties caused the system in question to behave the way it did, no model can claim to involve a "complete set of properties" the way the PBR proof invokes (unless "completeness" is defined in the provisional sense of "sufficient to get the predictions of the theory", but all theories do that, the properties are then just the states).

Let me say it like this: if one believes that ontic elements actually underpin a theory that does not refer to them, then one must hold that any statistical interpretation of the states of the theory must be built from ensembles of those ontic elements. But if the theory does not actually construct its states that way, it would be quite a coincidence if it could be interpreted that way. The key point is, wave functions can still be viewed as epistemic (as I do) if one simply asserts the very realist attitude that the epistemic states of any theory are always going to be the same as the ontic states of that theory (because the latter doesn't really exist independently of the former, there is no such thing as ontic states of a theory that could ever be distinguished from the epistemic states of that theory). No properties, no proof.

I think that you appear to be undervaluing the immutability of symmetries on the grounds that these symmetries can be contextualized in a myriad of different ways. In it's simplest form the true reality that some people chase is equivalent to arguing over whether the car was doing 70 mph or the ground was doing 70 mph under it. In more complex circumstances this non-physical coordinate attribute vastly changes the character and even apparent identity of what reality is. Even your "dressed atoms" is simply a regrouping of coordinates such that variable sets are regrouped as fewer sets of different variables.

Absolutely, that's the point-- we must not reify our coordinates, it would be an example of the mind projection fallacy. But that's just the coordinate projection fallacy-- the mind projection fallacy goes much deeper. It must extend to everything the mind is doing, because as soon as we think we can use our mind to tell the difference, we are committing the mind projection fallacy. We cannot have it both ways, which is just what Jaynes appears to do-- if he disagrees with something, it is the mind projection fallacy, but if he agrees with it (like "atoms are real"), then he thinks his mind can tell the difference between when it is projecting and when it isn't. I cannot imagine how he thinks he can navigate that core logical inconsistency.

 

[Ken G]

Well, you tell me. The fact is that this is exactly what you do, from the thread "Quantum Eraser and Its Implications":

Well, that might be what your incorrect interpretation of my statements is doing, but it is certainly not what I did. I don't understand why you can't get this: when we perceive an outcome to an experiment, to label that as a "nonunitary outcome", we must apply the concept of unitarity. This is an ontological entity borrowed entirely from a conceptual framework (the mathematics of linear maps of the Hilbert space, with whatever mathematical detail one wishes to get into). What I am saying is the thing that borrows ontological elements from mathematical frameworks is called the conscious intelligence of the human mind. I hardly find that controversial, yet somehow you cannot seem to admit this basic fact to yourself. I am left to wonder why you find it so important to block that knowledge, I usually associate that reaction with less scientific circles, but I guess it goes to show that scientists are humans too.

 

[my_wan]

How can you tell in which cases we are working with a "useful fantasy" about the reality and which cases we are working with the actual reality? To even make this language internally inconsistent, we must accept that even fantasies have a sliding scale of connection to reality, which is just what I mean by "usefulness", but never cross a line into being something fundamentally different from a fantasy-- all that demonstrably changes is the usefulness of the fantasy.

We can only clarify the empirical data such that more of our "useful fantasies" are known to be so. So yes, they do have a sliding scale. The scale just doesn't and never will go far enough to prove what reality is. Even a seemingly perfect unification theory or TOE can't do that. I'll get to what your missing wrt immutable facts shortly.

Indeed, and this is the central point. I'm not trying to divert this thread into a discussion of my personal philosophical opinions, this issue is right at the heart of just exactly what it is that PBR has proved about valid interpretations of quantum mechanics. PBR have adopted a very narrow view of what realism is, too narrow to be able to claim that they are using "only mild assumptions." Their version of realism is indeed often adopted by scientists, but I claim that it is internally inconsistent with science.

So what if it did take a narrow view? That just means it was successful in putting constraints on what is and isn't, within that narrow view, valid interpretations and extended modeling attempts of QM. Yet within that narrow view it did succeed in placing those constraints, i.e, established a symmetry that all future models, ontic or epistemic, must deal with. Even if it becomes moot in a deeper theory it must still deal with it in the domain in which it was defined.

And I would say the simple path that avoids any such incongruences is simply recognizing that any ontological statements we choose to make, whether they be about hurricanes or atoms or any physical "properties" of our world, are all going to be effective and useful pictures that we are choosing to borrow from conceptual structures like mathematics or everyday experience, and have no separate "existence" in the real world-- they exist only in the conceptual structures that we borrow them from. Same for properties-- so we can use properties within the context that they serve us, but we cannot prove things from using them, we cannot let a picture drive our logic that tells us what kinds of interpretations of quantum mechanics are possible, unless we allow that our proof only applies to those who would enter into our picture, and make our "mild" assumptions.

What you seem to miss is the fact that once a valid conceptual structure is established then any deeper model that uses an entirely different conceptual structure must still either conform to those symmetries within the domain they were supplied or demonstrate where they are wrong. Yes, same for properties. If theory A uses property set A and a deeper theory B uses property set B then theory B must provide for property set A within the domain of theory A. Exactly because valid symmetries are immutable, unlike to the conceptual structures you seem to think everybody is stuck on.

The issue here is, which should we regard as the "null hypothesis": that the ontic entities we create in our language about reality really are the foundational basis of the universe, or that they really are only what we can demonstrate them to be (ideas we create in our language and our mathematical theories, which are then transplanted from the conceptual structures in which they demonstrably exist and used in physical contexts where they do not demonstrably exist).

All I am saying is this: the true realist must adopt the latter, not the former, as their null hypothesis, because to do otherwise is a basic category error.

So a true realist must adopt the null hypothesis that nothing real exist. Well, I guess you already know what a true Scotsman must adopt don't you.

It is fully realistic to notice category errors, that's not a mind projection fallacy. Ironically, the mind projection fallacy is an identification of a particular type of category error, and I claim that my approach is the one that avoids mind projection fallacies.

So if we adopt this null hypothesis then there is really no point in defining no-go theorems, it is settled. Only then we wouldn't have constraints, that may be mooted but will never go away in any theoretical structure, as theoretical tools for deriving a more "useful fantasy". Whatever category error you think may be involved in fact produced constraints on any model, ontic or epistemic, that is very useful to theorist. The null hypothesis is that we don't know, but we'll push every possibility to see where anyone of them breaks. Taken your form of the null hypothesis involves invalidating possibly extremely valuable theoretical constructs.

It doesn't, it's just another such analogy taken from physics. The hurricane analogy serves admirably, it is a perfect example of what I mean when I say that scientific ontologies are contextual, provisional, and goal-oriented, and that is also the reason that if we wish to imagine that systems have "properties", we should not use that picture to drive a logical necessity that these properties must determine the behavior of the system.

So how we contextualize the description a hurricane changes something about what the hurricanes properties? So let's make them go away, just define them out of existence. More seriously, your null hypothesis does in fact properly define some very serious limits on science. But you are over generalizing the consequence of those limits. So much so that you are effectively ruling out a priori some potentially "useful fantasies" of immense power and usefulness. All the scientist i know are well aware of the limits you null hypothesis entails. But you appear to be taking it to such extremes, while apparently accusing scientist of making claims with their analogies they are not making.

That is actually reverse logic-- the usefulness of properties stems solely from the behaviors of the systems, not the other way around, and the usefulness of the property concept is contextual, provisional, and goal-oriented, but not unique and not logically closed.

Of course it's not unique. Do you think Susskind actually intended to say there was a airplane propellers around black holes? No. It was to illustrate a symmetry, and a valid symmetry is not provisional. It is ONLY provisional if you think he was really talking about airplane propellers around black holes!

It should never appear in any proof of anything general, and it should never be viewed as a "mild" assumption, but rather, it is the assumption that colors everything that results from it.

So airplane propellers around black holes colors our presumptions about what's around black holes? That's how much sense you make when you limit yourself to the particular context under which a symmetry is defined, such as the PBR theorem. Nor does your claim of what the paper said, or how your claim it is interpreted by scientist, have anything to do with how scientist think about the details of what the paper claimed.

True, but if atoms are real, and dependent on other things for that reality, then we must also assert what those other things are or else we cannot coherently talk about what an atom is.

No. Just as the hurricane analogy illustrated you don't even have to know atoms exist to describe it just as well. Simply use classical thermodynamics instead of statistical mechanics. Oh, by the way, the PBR paper title used the term statistical in the sense it was used in the development of classical thermodynamics, not the sense it was used in developing statistical mechanics. At one time they were thought to be indistinguishable theories differing only in ontologies, until Einstein came along with his paper on Brownian motion. Do you want the whole world to adopt your null hypothesis and forget even thinking Brownian motion, or it's modern equivalent?

Again, the escape from this paradox is simple-- there is no need at all to regard atoms, or hurricanes, as real, so we can talk about them the way we should be talking about them: as concepts and pictures that we evoke for some specific and contextual purpose.

We do. That's exactly why QM doesn't make such ontological claims one way or the other, and contains no contextual model at all that is empirically distinguishable. If we had just one then we could contextualize it any way we want because of how symmetries work. But we don't even have one, outside the math. And here you are telling us we shouldn't even look for one. Einstein shouldn't have looked at Brownian motion by such standards!

Since the limiting truth buried in your over-generalizations are is nearly universal among the scientist I know, with varying degrees of leaning towards those generalizations as their guide, I seeing this debate as moot. But the day science is no longer allowed to look for Brownian motion, which is what PBR symbolically did, due to a universal null hypothesis I wouldn't even call it science anymore. Science by definition ask questions in every possible context, not just those deemed worthy by a philosophical null hypothesis. As long as the debate is moot I see no more reason to continue.

 

[bohm2]

Just to add the newest paper on PBM. The authors also cite Leifer's blog:

Completeness of quantum theory implies that wave functions are physical properties

http://arxiv.org/PS_cache/arxiv/pdf/1111/1111.6597v1.pdf

 

[Ken G]

What you seem to miss is the fact that once a valid conceptual structure is established then any deeper model that uses an entirely different conceptual structure must still either conform to those symmetries within the domain they were supplied or demonstrate where they are wrong.

I'm not missing that, I'm well aware of it. Indeed, it's pretty much what I'm saying--we should always expect our new theories to mostly trash the ontological entities of our old theories, yet also explain why the old theories worked in the domain that they worked. So it has always been, so it will likely always be in physics. So what this means is, don't take the ontological elements of any theory too seriously-- they are ultimately all epistemic, yet somehow we need constant reminding of this, and don't seem to really get it until the next theory does come along.

Yes, same for properties. If theory A uses property set A and a deeper theory B uses property set B then theory B must provide for property set A within the domain of theory A. Exactly because valid symmetries are immutable, unlike to the conceptual structures you seem to think everybody is stuck on.

The problem with what your saying is in the word "immutable." I would simply say that an approximate symmetry is just that-- an approximate symmetry. It might even be quite an accurate approximation in most contexts, but the next theory will always show the context where it is not so accurate. I don't see anything "immutable" there, I just see that good theories remain good theories when better ones come along. So it will be with quantum mechanics-- but there will still never be a theory with a "complete set of properties" that determine what happens. Instead, indeterminacy will be our constant companion, because that's just how science works, and always has-- even when we pretended to ourselves that it was not working that way (as in classical mechanics and the concept of an exact position and momentum).

So a true realist must adopt the null hypothesis that nothing real exist.

No, that would certainly not be realism. Realism, is by definition, the idea that something real does exist. I am a realist. But what I am saying is that saying something real exists, and giving it properties, are two completely different things. What is "realistic" is to recognize that giving reality properties is always going to be useful, contextual, and goal-oriented behavior-- but it's never going to be the truth. That's just not what science has ever done-- it has always borrowed its ontologies from mathematical patterns, that it finds useful to include in some theory or other. What I don't get is, when it is perfectly demonstrably clear that this is what science does, why should we feel we need to pretend we are doing something different?

So if we adopt this null hypothesis then there is really no point in defining no-go theorems, it is settled.

Not so. No-go theorems are fine, but they are only as good as their assumptions. What better example of that was there but von Neumann's no-go hidden variable theorem? It sure didn't stop Bohm, and now we have a host of members on this very forum who are interested in Bohmian hidden variables. So much for no-go theorems! What a no-go theorem actually does is point to the assumptions you need to relax to avoid the theorem, but in the case of PBR, since they adopt the assumption that a complete set of properties determines all outcomes, it's pretty clear what assumption can be dropped for those seeking epistemic interpretations of quantum mechanics.

The null hypothesis is that we don't know, but we'll push every possibility to see where anyone of them breaks. Taken your form of the null hypothesis involves invalidating possibly extremely valuable theoretical constructs.

No it doesn't, nothing I say invalidates even a single theoretical construct. I'm fine with theoretical constructs, I just call them by their true names-- borrowed ontologies from mathematical patterns. I say the construct exists in one place: the realm of mathematics. Again, I'm amazed it is so common for people to reject that and want the constructs to jump over into absolute truths about the real world (like "atoms are real" and so on).

So how we contextualize the description a hurricane changes something about what the hurricanes properties? So let's make them go away, just define them out of existence.

But that's just it-- we don't need to define them out of existence, they never existed in the first place, anywhere except where they are already defined: as conceptual patterns, often mathematical in nature, sometimes merely descriptive-- but never anything but conceptual patterns, that's what I mean by useful fantasies. A hurricane is a useful fantasy, an atom is a useful fantasy. Langauge is labeling the labors of our minds. To claim anything else is nothing other than the mind projection fallacy, Jaynes is hoisted on his own petard.

So much so that you are effectively ruling out a priori some potentially "useful fantasies" of immense power and usefulness.

How is recognizing that something is a useful fantasy "ruling it out"? It's a useful fantasy, that's why we use it. Nothing ruled out at all, just calling it by its true name to avoid fooling ourselves (given that, as Feynman said, we are the easiest ones to fool).

All the scientist i know are well aware of the limits you null hypothesis entails.

Then why are you objecting to it? The fact is, scientists have a very had time with those limits, they treat it as a bitter pill they would rather not swallow. But it isn't so bitter, it's just the truth. PBR assumed that a complete set of properties determines everything that quantum mechanics is trying to describe and predict. Useful fantasies are fine, but you cannot prove things from them.

It was to illustrate a symmetry, and a valid symmetry is not provisional.

Yes it is, in science a valid symmetry is provisional. Everything is provisional, the concept of "valid" is provisional. Symmetries were made to be used, then broken, then used again. It's all provisional, science is the art of manipulating provisions. It always is, this is just constantly seen.

Nor does your claim of what the paper said, or how your claim it is interpreted by scientist, have anything to do with how scientist think about the details of what the paper claimed.

I'm not sure what you are claiming here, so I just have one question: did PBR, or did they not, assume that there is some "complete set of properties" that determine everything that happens to the systems that quantum mechanics is trying to predict and understand? Did they, or did they not, make this assumption about how the systems could behave, above and beyond how the quantum mechanical state treats their behavior, in order to learn something about how to interpret those states?

Do you want the whole world to adopt your null hypothesis and forget even thinking Brownian motion, or it's modern equivalent?

I don't understand what your asking, nothing in my null hypothesis requires ignoring the useful fantasy of the causes of Brownian motion that are invoked in any particular theory. Is it possible you think I'm advocating that science stop participating in useful fantasies? No, I never said it should do that, that has been the stuff of scientific progress for thousands of years. What I am saying is that we should stop pretending that we have been doing something else. You tend to agree with me, then turn around and say I'm wrong! Perhaps you are simply misinterpreting what I'm saying to make it wrong?

We do. That's exactly why QM doesn't make such ontological claims one way or the other, and contains no contextual model at all that is empirically distinguishable.

This is what I mean-- you are agreeing with me. Then you say my approach doesn't allow Einstein to try to explain Brownian motion? That doesn't make any sense, it is perfectly correct for good science to look for useful fantasies. What is wrong is imagining they are absolute truths instead-- like "atoms are real." Mind projection fallacies.

 

[Ken G]

Just to add the newest paper on PBM. The authors also cite Leifer's blog:

Completeness of quantum theory implies that wave functions are physical properties

http://arxiv.org/PS_cache/arxiv/pdf/1111/1111.6597v1.pdf

Here's a quote from that abstract: "...function represents
incomplete (subjective) knowledge about some underlying physical properties. Recently, Pusey et al. [arXiv:1111.3328, 2011] showed that the latter, subjective interpretation would contradict certain physically plausible assumptions, in particular that it is possible to prepare multiple systems such that their (possibly hidden) physical properties are uncorrelated."

There it is folks, clear as a bell: these authors interpret the PBR result as referring to ramifications of physical properties. Who said that any such thing as a physical property even exists? Note they are not talking about just elements of some theory.

 

[Fredrik]

There it is folks, clear as a bell: these authors interpret the PBR result as referring to ramifications of physical properties. Who said that any such thing as a physical property even exists? Note they are not talking about just elements of some theory.

Yes, it's clear that they think of the term "physical property" as a primitive. (The term means the same thing to them as it does to a person who doesn't know mathematics or physics. That's not necessarily a bad thing, but it's something we need to keep in mind when we read the rest of their comments). The end of the article makes this even clearer.

These conclusions were reached under two assumptions, which we argue are necessary. The first is that quantum theory is correct (if this would not hold, the question of whether the quantum state is a physical property does not make sense)​

A similar interpretation of the mathematical part of the PBR article would say that if QM is correct, and the probabilities of measurement results are determined by physical properties (i.e. the ontic state in the ontological model represents physical properties), then state vectors are physical properties. (I would still say that this is an interpretation of the PBR result, not the actual result).

I haven't studied the details of Colbeck & Renner's arguments, but I looked at the article they keep referencing all the time (link) because they're using the result they found there. Maybe it's just me failing to understand what they're doing, but the claim in that article looks extremely trivial to me. They assume that the probability assignments of QM are correct, and then argue that there can't exist any additional information (in addition to the quantum state) "that is useful to predict the outcome". I don't really see how the assumption is different from what they're trying to prove.

I find it really weird to assume that QM is correct. There are infinitely many quantum theories, but we seem to be talking about just one of them. So now we're assuming that there's an ontological model for that theory, and that the ontic states in that ontological model represent physical properties. These are some really huge assumptions. Not entirely implausible, but still huge.

 

[Len M]

No, that would certainly not be realism. Realism, is by definition, the idea that something real does exist. I am a realist. But what I am saying is that saying something real exists, and giving it properties, are two completely different things. What is "realistic" is to recognize that giving reality properties is always going to be useful, contextual, and goal-oriented behavior-- but it's never going to be the truth. That's just not what science has ever done-- it has always borrowed its ontologies from mathematical patterns, that it finds useful to include in some theory or other. What I don't get is, when it is perfectly demonstrably clear that this is what science does, why should we feel we need to pretend we are doing something different?

I’m not wishing to detract from the theme of the thread, or invoke a side discussion into the philosophical definition of realism, so strictly just for my interest only, a clarification of the kind realism that you invoke would be of interest to me.

I think of the strict definition of realism in a philosophical sense as consisting of two parts:

1. A notion of “reality” conceived of as totally independent of our possible means of knowing it, along with the hypothesis that we do have access to the said reality, at least in the sense that we can say something “true” about it.

We can not prove the hypothesis in the way that we empirically verify scientific models, so the “true” element of that statement is a philosophical statement, in the sense that it may be correct or it may not be – we will never know, all we can do is to believe in it, in the sense of having a "faith" that we can say something "true" without ever knowing that to be the case.

2. A representation of mind independent reality worked out from the phenomena, i.e. from human experience. This representation, in science, is constructed without any need to include mind independent realty as a necessary ingredient in this process of representation.

The representation is used to impart the something “true” about mind independent reality, but the “true” element is a philosophical statement, again in the sense that it may be correct or it may not be – we will never know.

So a realist (of any of the usual flavours) to my mind would, firstly admit that the notion is a philosophical one, but secondly “believe” that the notion is correct, though it can’t be proven.

Now you seem to be saying that one can be a realist without adopting a “belief” that the said realist can say something "true" about mind independent reality.

I’m just, how shall I say, uneasy over your definition. I’m not saying its wrong; it just seems different to how I understand realism. As best as I can infer, you would say that the properties of physics are a useful means in which to do physics rather than implying that those properties are a “true” (“true” in the sense in which I would expect a philosophically aware realist to use the term) representation of mind independent reality. I would say that you make no reference at all to mind independent reality in terms of these properties – you don’t see it as any issue.

Now actually I agree with that, but I would never think of myself as a realist, I would say I am much closer to idealism. I do believe (strongly) that there “exists” a mind independent reality, but equally strongly, I can’t see how we are ever going to penetrate this reality through science. So whilst I consider that I adopt a stance of idealism, it is not radical idealism, I do actually consider that our reality “emerges” (and I use the word "emerge" here in no way to impart any kind of familiar usage, I just can't think of any other way to say it) in some manner from mind independent reality and that that "emergence" gives rise (in an undefined manner) to the consistencies inherent within our reality, but I have no realist “belief” that we can say something “true” about that mind independent reality (or the "emergence" to our reality) using science. I don’t think there is any justification to believe that what exists outside of our reality is of a form that we would recognise in any manner, thus I can't take on board the "belief" that the realist has in thinking that we can say something true about mind independent reality in terms of science.

So I have to say, that I can’t help thinking that actually you are much closer to idealism than realism - you seem to have no "belief" that science can say anything "true" ("true" in the sense of how I would expect a philosophically aware realist to use that word) about mind independent reality. I understand (I think) what you mean when you assert you are a realist, I’m just not sure that label conforms with my understanding of what it means to be a philosophically aware realist. I know this is just abouit definitions and not substance - but I am interested how and why you may differ over my understanding of realism as it is defined in terms of philosophy.