Download 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.