Transcript Slide 1
Experimental Metaphysics Travis Norsen , Marlboro College (Vermont) “This could suggest to some that the question is a philosophical one. But I insist that my concern is strictly professional.” -J.S. Bell Outline: • Terminology (Realism, Idealism, Empiricism) • Idealism in Modern Philosophy and 19th Cent. • Copenhagen QM • Shelly vs (the argument for) Idealism • A classification of quantum theories • Primitive Ontology and Empiricism The central question of metaphysics: What is the relationship between consciousness and the external world? Two possible answers (focusing on perception): • Realism: (perceptual) awareness is awareness of objects in external reality • Idealism: (perceptual) awareness is awareness of something in the mind (ideas, internal representations of external objects, etc.) Idealism and empiricism • Empiricism: valid knowledge is based on observation, on what we experience in sense perception. • But what do we experience in perception? – Realism vs Idealism two very different “empiricisms” – Idealist empiricism has dominated philosophy… Some Idealist Philosophers • • • Locke: “It is evident to anyone who takes a survey of the objects of human knowledge that they are either ideas actually imprinted on the senses, or else such [ideas] as are perceived by attending to the passions and operations of the mind, or lastly, ideas formed by help of memory and imagination.” Hume: “It is a question of fact whether the perceptions of the senses be produced by external objects resembling them: How shall this question be determined? By experience surely; as all other questions of a like nature. But here experience is, and must be entirely silent. The mind has never any thing present to it but the perceptions, and cannot possibly reach any experience of their connexion with objects. The supposition of such a connexion is, therefore, without any foundation in reasoning.” Kant: “We are perfectly justified in maintaining that only what is within ourselves can be immediately and directly perceived... Thus the existence of a real object outside me can never be given immediately and directly in perception, but can only be added in thought to the perception, which is a modification of the internal sense, and thus inferred as its external cause… In the true sense of the word, therefore, I can never perceive external things, but I can only infer their existence from my own internal perception, regarding the perception as an effect of something external that must be the proximate cause … . It must not be supposed, therefore, that an idealist is someone who denies the existence of external objects of the senses; all he does is to deny that they are known by immediate and direct perception … “ The argument for idealism Hume: “…when men follow [the] blind and powerful instinct of nature, they always suppose the very images, presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other. This very table, which we see white, and which we feel hard, is believed to exist, independent of our perception, and to be something external to our mind, which perceives it. Our presence bestows not being on it: Our absence does not annihilate it. It preserves its existence uniform and entire, independent of the situation of intelligent beings, who perceive or contemplate it. “But this universal and primary opinion of all men is soon destroyed by the slightest philosophy, which teaches us that nothing can ever be present to the mind but an image or perception, and that the senses are only the inlets, through which these images are conveyed, without being able to produce any immediate intercourse between the mind and the object. The table, which we see, seems to diminish, as we remove farther from it: But the real table, which exists independent of us, suffers no alteration: It was, therefore, nothing but its image, which was present to the mind. These are the obvious dictates of reason; and no man who reflects ever doubted that the existences which we consider when we say, this house and that tree, are nothing but perceptions in the mind, and fleeting copies or representations of other existences, which remain uniform and independent.” The argument: Genuine awareness must be “immediate and direct” (“immediate intercourse”), must involve no means Our actual relationship to external objects is not immediate and direct; we’re (apparently) aware of external objects in some definite way which can vary even when the object doesn’t ----------------------Therefore our relationship with external objects isn’t one of genuine awareness; we are aware only of something “internal”, some aspect of the means 19th century idealism Henry Krips (SEP): “...during the nineteenth century observation, and specifically vision, were both reconceptualized not as a Kantian universal [mental] faculty but rather as physiological processes. In particular, it was assumed that observable phenomena were conditioned, not by universal forms of sensible intuition, but rather by the sorts of external physical factors that affected bodily and specifically physiological processes more generally.” 19th century thinkers “physiologized the Kantian conception of observation” Mueller, 1838: “That which through the medium of our senses is actually perceived … is … merely a property or change of condition of our nerves…” What we perceive is the means of perception – but understood now as physiological rather than mental. QM’s Founding Fathers • Krips, continuing the previous quote: “Bohr extended this position by proposing that the ‘external procedures’ that affect the forms of sensible intuition include the processes of observation themselves. Thus Bohr stood at the end of a long historical trajectory. Kant conceived the apparatus of observation as an inner mental faculty, analogous to a pair of spectacles that mediated and in particular gave form to and interpreted raw sense impressions. Neo-Kantians projected the interpretative aspect of vision outwards, reconceiving it as a bodily, and specifically physiological process…. Bohr took this further by including observation as [affecting] not merely what we see but also the terms in which we describe it.” QM’s FFs physicalize the “veil” (which had been already physiologized in the 19th cent.) Bohr’s Veil Mueller’s Veil mind Kant’s Veil The Quantum “Veil of Perception” The QM FFs were explicitly motivated by idealist-empiricist philosophy… – Heisenberg: new experiments required “a radical change in the forming of physical concepts.... In this situation I thought of an idea that I had read in Einstein's work, namely the requirement that a physical theory should contain only quantities that can be directly observed.‘” …and analyzed “measurement” metaphysically (i.e., experiment = experience)… – – Heisenberg: “the frequencies and amplitudes associated with the line intensities .... could be observed directly.” Born: “In physics, all `experience‘ consists in … instruments‘ pointer readings.‘” …and regarded the non-trivial interaction between micro-object and macro-measuring-apparatus as a (physicalized) locus of Kantian distortion, which prevents us from genuinely obtaining knowledge of the micro-objects: – – – Heisenberg: “We can no longer speak of the behavior of the particle independently of the process of observation. As a final consequence, the natural laws formulated mathematically in quantum theory no longer deal with the elementary particles themselves but with our knowledge of them. Nor is it any longer possible to ask whether or not these particles exist ... objectively...” Heisenberg: “When we speak of the picture of nature in the exact science of our age, we do not mean a picture of nature so much as a picture of our relationships with nature. The old division of the world into objective processes in space and time and the mind in which these processes are mirrored … is no longer a suitable starting point…. Science no longer confronts nature as an objective observer, but sees itself as an actor in this interplay between man and nature. The scientific method of analysing, explaining and classifying has become conscious of its limitations, which arise out of the fact that by its intervention science alters and refashions the object of investigation. In other words, method and object can no longer be separated.” Bohr: “There is no quantum world. It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we can say about Nature.‘” Summary: Copenhagen as idealist metaphysics, physicalized • Idealist Metaphysics: the non-negligible causal interactions constituting our means of awareness of certain ultimate objects distorts the objects, leaving us aware only of some “phenomenal” appearance • Physicalized: the reality-appearance (or object-subject) boundary is placed at the micro-macro boundary (and then renamed) – “experiment” replaces literal observation as the locus of the distorting interaction (i.e., “experiment” is treated metaphysically) Now let’s turn to assessing the argument for idealism… Another formulation of idealism… Zeilinger, defending Copenhagen against the claim that we need a QT w/o Observers: “I suggest that the very austerity of the Copenhagen interpretation ... speaks very much in its favor. Indeed, its basic attitude toward the fundamental role of observation represents a major intellectual step forward over naive classical realism. In classical physics, observation is often regarded as a secondary concept, with the elements of the real world being primary. Yet, it is obvious that any statement about nature has to be based on observation. What could then be more natural than a theory in which observation plays a more fundamental role than in a classical worldview? What could be more sensible than the theory itself acknowledging that any statement about the world has to make reference to observation? .... Indeed, as in the case of the measurement paradox, the paradoxes constructed by opponents of the Copenhagen interpretation are always based on some realistic pre-quantum notions about how the world ought to be brought into the discussion through the backdoor. In fact, there is never a paradox if we realize that quantum mechanics is about information.” Note the transition from empiricism (“any statement about nature has to be based on observation”) to idealism: because they are based on observation, statements about nature are not after all about nature, but are about observation. …and Shelly’s response ”...does Zeilinger truly believe that `quantum mechanics is about information'? Information is always information about something. Therefore, shouldn't quantum mechanics then be regarded as being about that something? Quantum mechanics tells us about atoms and chemical bonding and high-temperature superconductivity. Of course, it also provides us with information about these things. But it does so precisely because it is about the things themselves.... Moreover, it would not be at all sensible for a theory to acknowledge that `any statement about the world has to make reference to observation,' since [this] is plainly false. Statements about history are not statements about history books, and statements about dinosaurs are not statements about fossilized dinosaur bones. And even statements concerned with the present, though they are typically based rather directly on observations – if not our own, then somebody else's – are usually not about those observations. Although it is presumably true that the justification of any statement about the world must be based, at least in part, on experience or observation, there is nothing in Zeilinger's assertion that `any statement about nature has to be based on observation' to suggest, or even make plausible the idea, that observation has a fundamental role to play in the formulation, as opposed to the justification, of physical theory. “What Zeilinger terms `the austerity of the Copenhagen interpretation’ is very much like the austerity of solipsism, and it suffers from similar defects. What results from this austerity is not merely implausible, but also deficient in the theoretical simplicity afforded by an appeal to something outside ourselves.” My interpretation: We must distinguish (for conceptual conclusions) the justification from the content. Or, more generally, we must distinguish the means of awareness (the way we are aware) from the object of awareness (what we are aware of by that means). We must refuse to make the means into a new object (which displaces the original one). Analogy: cutting a cake with a knife • • • • In one sense, the cutting is indirect because we use a knife. We only cut the cake by means of the knife. But does that mean we’re not really cutting the cake after all, but only cutting the knife? Must cutting involve “immediate intercourse” between you and the cake? No! Whoever says it should just doesn’t understand cutting … or uses that word to mean something other than what we mean. Awareness is like cutting – it has both an object and a means, and the existence of the means does not prevent (but rather makes possible) its “reaching” the object: – just because we know about dinosaurs by means of fossils, doesn’t mean we really only know about the fossils – just because we know about chemical bonding by means of the information contained in QM, doesn’t mean we really only know about information – just because we perceive an apple by means of a retinal image (nerve impulses, sensory qualia, etc.), doesn’t mean we really only perceive the retinal image (impulses, qualia, etc.) Idealism Deconstructed • • • The fundamental argument for idealism seems to be that a means of (perceptual) awareness cuts us off from external objects. Idealists say that, wherever we are aware of X by means of Y, we are really only aware of Y. But that makes no more sense for awareness than for cutting. Once you see this, the argument for idealism just disappears. The basic premise is that awareness should be “immediate and direct”. Then: since it isn’t, we’re not actually aware. Thus: our means of awareness prevents us from being aware of external objects. Rand’s reductio summary: “man is limited to a consciousness of a specific nature, which perceives by specific means and no others; therefore, his consciousness is not valid; man is blind, because he has eyes…” …and now finally back to QM… Two aspects of Bell’s critique of QM • The positing of a “split” physical world is the fundamental problem (“shiftiness” being merely a symptom): ``What worried me then was how to get rid of that division. I was looking for some reformulation of the theory that would permit its elimination. It was clear to me then that the hidden-variable approach would be one such formulation. If you gave definite properties – `hidden variables' – to the elementary quantum particles, you don't have to be concerned that the classical apparatus has definite properties. Everything has definite properties. It is just that they are more under our control for big things than for little things.” (vs. any metaphysical treatment of “measurement”) • What we observe is physically real: “The beables must include the settings of switches and knobs on experimental equipment … and the readings of instruments. `Observables’ must be made, somehow, out of beables.” (vs. idealism) A classification of quantum theories Realism “Experiment” as metaphysical •Contextual HVTs ? •Modal Theories ? “Experiment” as physical •Bohmian Mechanics •GRWm •GRWf Naïve Realism Idealism •Non-contextual HVTs (“Naïve Realism about Observables”) •Copenhagen •Information •MWI •RQM Conclusion: Primitive Ontology and Empirical Adequacy • If we say theories should agree with what we observe (empiricism) … … and if what we observe is real, external, physical objects (realism) … … then theories need POs in order to be empirically adequate. • Bell: serious theories as “mathematically consistent continuations of the visible world into the invisible” • Shelly (et al.): “it is the entities of the PO that make direct contact with the world of our experience.” • The goal of “empirical adequacy” is to account for the fact – not the subjective experience, but the experienced fact – that material objects (tables, pointers, etc.) move in certain ways.