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Luboš Motl keeps insisting quantum mechanics invalidates ontology, and has made ontology obsolete, just like phlogiston. What would metaphysics without ontology look like, where words like "existence" and "reality" are banned?

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Are you sure this is a question about physics and not philosophy? –  Joe Z. Feb 14 '13 at 13:45
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Motl wrote about "ontology" within quotation marks: "If the word "ontology" is added with the purpose to ban the plurality of allowed sets of consistent histories, then the whole philosophy of "ontology" is just scientifically invalid." And: "If by "ontology", you mean the assumption that one set of questions and/or consistent histories is objectively "more real" than others, then - as I have explained 500 times already - the discovery of quantum mechanics has proved that "ontology" was a pseudoscience much like phlogiston." Big ifs? –  Gugg Feb 14 '13 at 16:00
    
"Shut up and multiply" interpretation works always. You can't take "existence" and "reality" out of it. –  zaarcis Feb 17 '13 at 11:53
    
@zaarcis You're referring to... biology? :) –  user3164 Feb 17 '13 at 14:03
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@zaarcis No, I was actually referring to the exegesis of Genesis 9:1. The more usual expression in the context of QM is "Shut up and calculate!" :) –  user3164 Feb 17 '13 at 14:45
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3 Answers 3

What would a quantum interpretation without ontology be like?

Short Explanation: It looks like instrumentalism. Instrumentalism avoids the debate between anti-realism and philosophical or scientific realism. It may be better characterized as non-realism. Instrumentalism shifts the basis of evaluation away from whether or not phenomena observed actually exist, and towards an analysis of whether the results and evaluation fit with observed phenomena. By abuse of language, a bare instrumentalist description could be referred to as an interpretation, although this usage is somewhat misleading since instrumentalism explicitly avoids any explanatory role; that is, it does not attempt to answer the question why.


ADDENDUM NOTES

Long Explanation: Ontological realism is the view that physical objects exist independently of our own minds. Epistemological realism is the view that statements are true or false independently of whether we know or believe them to be true. Metaphysical realism is the view that what is real exists just as it is independently of the subjects that experience it.

Realism in a general way is the thesis that science aims at truth and that acceptance of a theory includes believing that it is true. The main line of argument for realism is ‘‘explanationist’. This means, essentially, that the explanatory achievements of theories count favorably in their epistemic evaluation. If there were no truth to theory, one would be at a loss to explain, not just what is observed, but also the success of theory in explaining and predicting what is observed. Understanding why theories work as well as they do is necessary for improving them.

A barrier to supposing that a realist explanation is needed is that the predictive result might also be predicted by rival theories. To generate the strong underdetermination problem for scientific rival theories, we start with a theory H, and generate another theory G, such that H and G have the same empirical consequences, not just for what we have observed so far, but also for any possible observations we could make. Quantum physics gives genuine examples of empirical equivalence. If there are always such strongly empirically equivalent alternatives to any given theory, then this might be a serious problem for scientific realism.

There are non-empirical features (superempirical virtues) of theories such as simplicity, non-ad hocness, novel predictive power, elegance, and explanatory power, that give us a reason to chose one among the empirically equivalent rivals. The underdetermination problem motivate the conclusion that science can never give us knowledge of the unobservable world, and that our best scientific theories are empirically adequate rather than true. Realists argue that we need to explain the overall instrumental success of scientific methods across the history of science. But the realist demand for explanation of every regularity leads to infinite regress. Since there are many ontologically incompatible yet empirically equivalent theories, we have no reason to choose among them and identify one of them as true, thinks the non-realist.

Inference to the best explanation is a rule of inference according to which, where we have a range of competing hypotheses, all of which are empirically adequate to the phenomena in some domain, we should infer the truth of the hypothesis which gives us the best explanation of those phenomena. But the non-realist thinks that some ‘principle of privilege’ is required from realists if we are to think that the collection of hypotheses that we have under consideration will include the true theory. The best explanatory hypothesis we have may just be the best of a bad lot, all of which are false. In other words this argument challenges the proponent of the realist's best explanation rule to show how we can know that none of the other possible explanations we have not considered is as good as the best that we have. Unless we know that we have included the best explanation in our set of rival hypotheses, even if it were the case that the best explanation is true, this would not make an acceptable rule of inference.

The realist and the non-realist disagree about the purpose of the scientific enterprise: the former thinks that it aims at truth with respect to the unobservable processes and entities that explain the observable phenomena; the latter thinks that the aim is merely to tell the truth about what is observable, and rejects the demand for explanation of all regularities in what we observe. The non-realist thinks that empirical adequacy is the internal criterion of success for scientific activity, that acceptance of the best theories in modern science does not require belief in the entities postulated by them, and that success of modern science relative to its aims can be understood without invoking the existence of such entities.

Non-realist-predictivists think that only successful predictions of previously unknown phenomena count as evidence, and realist-explanationists think that explanations of previously known about phenomena count as evidence, that the explanatory achievements of theories count favorably in their epistemic evaluation. There are many cases where the observation of one phenomenon allows us to predict the observation of another phenomenon but where the former does not explain the latter. For example, the fall of the needle on a barometer allows us to predict that there will be a storm but doesn’t explain it. There also seem to be theories that provide adequate explanations but that cannot make precise predictions. For example, evolutionary theory explains why organisms have the morphology that they do, but it cannot make specific predictions because evolutionary change is subject to random variations in environmental conditions and the genotype of organisms. Furthermore, there are cases of probabilistic explanations where the probability conferred by the explanans on the explanandum is low, so we cannot predict that the explanandum is even likely to happen although we can explain why it did if it does. Non-realists-predictivists think that explanatory power is a merely pragmatic virtue of theories and does not give us evidence for their truth, doesn't count favorably in their epistemic evaluation, explanations can be easily ad-hoc. The non-realist thinks that there is no evidence available in principle that can distinguish a theory’s truth from its utility and reliability in prediction. The realist contends that a theory’s predictive and explanatory success are evidence for it.

According to the deflationary theory of truth, to assert that a statement is true is just to assert the statement itself. For example, to say that ‘snow is white’ is true, or that it is true that snow is white, is equivalent to saying simply that snow is white, and this, according to the deflationary theory, is all that can be said significantly about the truth of ‘snow is white’. Philosophers often make suggestions like the following: truth consists in correspondence to the facts; truth consists in coherence with a set of beliefs or propositions; truth is the ideal outcome of rational inquiry. According to the deflationist, however, such suggestions are mistaken, and, moreover, they all share a common mistake. The common mistake is to assume that truth has a nature of the kind that philosophers might find out about and develop theories of. For the deflationist, truth has no nature beyond what is captured in ordinary claims such as that ‘snow is white’ is true just in case snow is white. A central characteristic of truth – one that any adequate theory must explain – is that when a proposition satisfies its “conditions of proof (or verification)” it is regarded as true.

It is often said that what is most obvious about truth is that truth consists in correspondence to the facts — for example, that the truth of the proposition that the earth revolves around the sun consists in its correspondence to the fact that the earth revolves around the sun. The so-called correspondence theory of truth is built around this intuition, and tries to explain the notion of truth by appeal to the notions of correspondence and fact. But it is far from clear that any significant gain in understanding is achieved by reducing “the belief that snow is white is true” to “the fact that snow is white exists”. Deflationists argue that truth is a shallow (sometimes “logical”) notion, a notion that has no serious explanatory role to play: as such it does not require a real theory, that would have to take the form of a genuine generalization.

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I assumed in my comment (and could be wrong about that) that the OP referred to this chat session. Perhaps this context is relevant? The chat originated from this question. –  user3164 Feb 14 '13 at 19:14
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@Gugg The question that originated the chat is unintelligible. I expanded my answer. –  Ricardo Feb 15 '13 at 12:20
    
There's one complication, that is specific to QM, that I seem to miss. Say, Motl believes a "bare" QM (in that it can't be improved upon in explanatory power) and, say, claims that, crucially, this bare QM itself implies that it allows for all consistent "ontologies" without privilege, but certainly excluding at least all classical "ontologies" (which are supposedly inconsistent with QM). Although there is no privilege among (many) QM-consistent "ontologies", QM-inconsistent (e.g. classical) "ontologies" don't get the same benefit. Where does that put him? (Does my formulation make sense?) –  user3164 Feb 15 '13 at 20:52
    
Motl's claim might also include that there is no conceivable improvement on the "bare" QM (in terms of explanatory power) - which would have to explain the bare QM working so well in the current experimental domain -, that is (also) classical. –  user3164 Feb 15 '13 at 21:14
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Where does that put Classical Ontology? Classical mechanics is loaded with ontologic hypotheses without any empirical counterpart. As examples the existence of an absolute time, the complete determination of objects, the strict causality law. Since some of these hypotheses are explicitly eliminated in quantum theory, there is no approximation procedure which leads from quantum mechanics to classical mechanics. Classical mechanics describes a empirical fictitious world. –  Ricardo Feb 16 '13 at 4:07
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What would a quantum interpretation without ontology be like?

I take it that an interpretation of quantum mechanics (QM) without "ontology", would (perhaps surprisingly) look like an interpretation that doesn't privilege any (QM-consistent) "ontology", i.e. one that allows all (QM-consistent) "ontologies", e.g. the consistent histories approach.

PS: I assume that it's called the consistent histories approach instead of interpretation (at least sometimes on Wikipedia) precisely for the reason that it doesn't privilege a particular "ontology".

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I do not think it is wise to entirely separate science from interpretation and ontology.

To give an example - when Newton proposed his theory of gravitation an immediate objection viewing it ontologically was what could it mean to have an action at a distance this question was only resolved with Einsteins theory.

Another example from the mathematical sciences is the invention of calculus, the objection this time pointed out by Bishop Berkelely quite forcefully was what were these fluxions that Newton used, they appeared to be the ghosts of departed quantities. To resolve this question took the invention of analysis to put the calculus on a rigorous basis.

A third example is the aether - it was seen to be the medium through which light travelled, and was definitely discarded after the Michaelson-Morley experiments and the discovery of relativity. This is the traditional view, but this is not quite correct. The aether was viewed as a mechanical medium as Newtons theory of mechanics was seen as the paradigm towards which all theories should aim. It was the idea of a medium that was mechanical that was disproved. In fact the ontological idea of a medium lived on, and is generally called a field in modern physics - aka the classical theory of fields & quantum field theory.

Physics without ontology is a kind of scientism. There is some truth to Motls thinking in that there is a great deal of technique within the physical sciences and one must master them. But one mustn't lose sight of the greater goal of obtaining an understanding of the world-out-there.

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A field isn't a medium. It's a strictly more basic idea: a mapping between space and some scalar or vector quantity without anything required to support that quantity. A medium is some stuff which is required to transmit or support some quantity. –  Rex Kerr Feb 15 '13 at 18:35
    
@Kerr: aren't you contradicting yourself? You say that a field requires no support, yet you specify a mapping between spacetime and a field? Is there such a thing as a bare field? A mechanical medium was reuired to transmit light mechanically, as in say a perfect liquid or the like. This is where the theory ether fell down, when it was understood that a field did not have to be understood mechanically. –  Mozibur Ullah Feb 16 '13 at 16:54
    
No, there is no contradiction in making a distinction between input variables and a medium. A medium presupposes that there's something (not necessarily mechanical) there. Variables don't. –  Rex Kerr Feb 16 '13 at 17:49
    
@Kerr: You're missed my point. Although you can at least conceptually have a bare spacetime, which is commonly taken to be a differentiable manifold. And you can take a field to be a manifold in itself, it is actually NOT a field until you attach to spacetime by some morphism. The morphism is part of the data. And this is before getting into what can these operations & manifolds physically mean. You appear to be confusing mathematical formalism with physical intuition. –  Mozibur Ullah Feb 16 '13 at 18:05
    
@Kerr: Variables may not presuppose anything to be there, but this is because this is mathematics and not physics. Its ontology is not clear-cut. –  Mozibur Ullah Feb 16 '13 at 18:10
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