Introducing Bruce Gregory, part two
Theories and Reality
Classical physics demonstrated the power of a language that
separates the observer and the observed, the subject and the
object. Surely there are facts about the way the world is
independent of what we say, and surely we can talk about the
world as it is independent of any observations. Quantum
mechanics, however, did not fit this framework The success of
quantum mechanics showed physicists that when they talk about the
atomic realm, they can no longer talk of a world whose behavior
can be described in the absence of a well-defined scheme of
measurement. In talking about the atomic world, the observed and
the observer cannot be separated the way they can be when we talk
about the world of everyday experience. To go beyond the realm of
classical physics, physicists had to give up the paradigm of a
detached observer and an independent reality.
In the final analysis, physics is only indirectly about the
world of nature. Directly, it is talk about experimental
arrangements and observations. Given a particular experimental
arrangement, physicists can predict the outcome of certain
measurements. There is nothing arbitrary about these outcomes.
Anyone with the requisite ability can replicate them ' they are
perfectly objective in this sense. Nor is there anything
arbitrary about the predictions. What is not given to physicists
by nature, but rather is invented by them, is what they say about
these outcomes, the language they use to talk about nature. If
physicists try to step outside the scheme of experimental
arrangements and observations to envision what sort of
independent mechanism in the world 'really' produces those
observations, in Feynman's words, they 'get 'down the drain',
into a blind alley from which nobody has yet escaped.'
How do we know what the world is like? We think our eyes give
us a representation of the way the external world really is, but
as the prologue points out in the example of the photograph of a
building, this too is a way of speaking ' a way of speaking based
on the notion of 'realistic' representation. In fact, theories
have been developed that do not endow the nervous system with a
representational function. In a recent book describing vision and
illusions of color, the biologists Humberto Maturana and
Francisco Varela say
Because these states of neuronal acidity (as when we see
green) can be triggered by a number of different light
perturbations (like those which make it possible to see
color shadows), we can correlate our naming of colors
with states of neuronal activity but not with
wavelengths. What states of neuronal activity are
triggered by the different perturbations is determined in
each person by his or her individual structure and not by
the features of the perturbing agent.... Doubtless ... we
are experiencing a world. But when we examine more
closely how we get to know this world, we invariably find
that we cannot separate our history of actions '
biological and social ' from how this world appears to
us.
Perhaps we should not be too surprised if we cannot grasp an
absolutely independent world. To paraphrase Charles Darwin, we
are organisms shaped, not by getting the world right, but by
surviving to leave offspring. Before we embrace the idea that
survival is invariably aided by getting the world right, that is
by representing the world 'correctly' in language, perhaps we
should look at the living things that have survived and left
offspring for hundreds and even thousands of times longer than
Homo saps. The frog, for example, sees a very different world
from the one we see. If frogs had language, it would be
illuminating to learn what they would say about how the world is
'really' put together. The perception of a causal world unfolding
in space and time, which serves our survival so well, may be only
a tool that works on the scale on which it evolved.
Some say quantum mechanics shows that experimental arrange-
ments compel electrons to take on certain values such as position
and momentum. But we can equally well say that there are no facts
about the paths of subatomic particles; instead, there are our
interpretations of the measurements we make ' interpretations in
terms of position and motion. Physicists discovered that they
cannot interpret their measurements in a language where position
and momentum are simultaneously precise.
The existence of a world we cannot see makes sense from a
physicist's point of view only if this world has observable
consequences. Physicists cannot 'see' quarks or gluons, but
quarks and gluons are elements of physical theory because they
lead to predictions that physicists can see. Talking as though
there are quarks and gluons helps physicists to make sense of the
world.
Knowledge and Reality
There is a sense in which no one, including philosophers,
doubts the existence of a real objective world. The stubbornly
physical nature of the world we encounter every day is obvious.
The minute we begin to talk about this world, however, it somehow
becomes transformed into another world, an interpreted world, a
world delimited by language ' a world of trees, houses, cars,
quarks, and leptons. In order to deal with the world we have to
talk about it (or measure it, or shape it ' in any case we engage
the world in terms of our symbols, whether we are building a
pyramid or a Superconducting Super Collider).
When people first talked about electrons, they thought of
them as perfectly respectable bits of matter ' too small to be
seen directly but otherwise no different from objects on the
scale we are familiar with. Einstein's argument that matter and
energy somehow must be equivalent suggests that all is not so
simple as it might at first seem; Dirac found we can talk of
electrons and positrons as being created out of nothing but
energy and being reduced to nothing but energy. Quantum mechanics
shows it is impossible even to picture these elementary
constituents of matter: They are required to be well behaved
localized entities whenever we detect them, but otherwise
diffuse, 'possibilities of detection' spread widely over space
and time.
Quantum electrodynamics replaces discrete electrons with talk
about excitations of an electron field: a field that, in addition
to harboring the probability of observing "normal' electrons,
teems with virtual electrons and positrons winking into and out
of existence. In superstring theory, electrons are the energy
states of incredibly tiny quantum strings vibrating in
ten-dimensional spacetime. These descriptions are different ways
of talking about the same world. The best way to understand the
role of a theory seems to be as a tool, a way of speaking,
appropriate or inappropriate to the task at hand.
It seems perfectly reasonable to ask whether leptons and
quarks are two kinds of "stuff" out of which the world is made.
Mathematicians, however, talk about numbers in much the same way
that physicists talk about leptons and quarks. A physicist's
world is made up of leptons and quarks because physicists talk
about their experiments in terms of leptons and quarks. In the
same way, the mathematician's world is made up of imaginary
numbers and infinite sets because imaginary numbers and infinite
sets are an essential feature of the discussions of contemporary
mathematics; an economist's world includes markets, supply, and
demand for a similar reason. The word real does not seem to be a
descriptive term. It seems to be an honorific term that we bestow
on our most cherished beliefs ' our most treasured ways of
speaking.
The lesson we can draw from the history of physics is that as
far as we are concerned, what is nail is float we regularly talk
about. For better or for worse, there is little evidence that we
have any idea of what reality looks like from some absolute point
of view. We only know what the world looks like from our point of
view. From a physicist's perspective, the behavior of the
physical world is most effectively talked about in the language
of quantum field theories.
The Conversation of Physics
If the current way of talking about quantum chromodynamics
continues, physicists will never see an individual quark or
measure its fractional electric charge. The effects of the color
force will forever remain invisible. Nature seems to conspire to
keep physicists from ever seeing her ultimate constituents ' or,
more accurately, the most successful ways of talking about nature
that physicists have found turn out to require that they speak in
terms of fundamentally unobservable elements. Yet most physicists
are committed to the reality of quarks. It is hard to imagine
working every day with an idea without being committed to its
reality. As Einstein said, "Without the belief that it is
possible to grasp reality with our theoretical constructions,
without the belief in the inner harmony of the world, there would
be no science.
The role of language is always easier to see when someone
else's language is involved. While physicists talk about quarks
the same way they talk about anything else, those who are not
working physicists have the luxury of stepping back and seeing
that quarks are a way of talking about the world ' a way of
talking that gives physicists power in describing and predicting
nature's behavior.
In Heisenberg's words, "What we observe is not nature in
itself, but nature exposed to our method of questioning. Our
scientific work in physics consists in asking questions about
nature in the language we possess and trying to get an answer
from experiment by the means that are at our disposal.' And
Bohr's, "It is wrong to think that the task of physics is to find
out how nature is. Physics concerns only what we can say about
nature.'
We have always dreamed of being able to talk about the world
in the right way ' to talk about the world in what the American
philosopher Richard Rorty ironically calls "nature's own
language.' The history of physics makes it hard to sustain the
idea that we are getting closer to speaking 'nature's own
language." Talk about quarks arises in the interaction between
physicists and the world; we interact with the world and create
interpretations of what this interaction means.
Truth as Procedure
Just as many mathematicians talk as though every statement
were either true or false, we human beings want to talk about the
physical world in the same way. Either matter is made up of
quarks or it is not. Either there is intelligent life outside the
solar system or there is not. Either 1978 was the snowiest winter
in Boston in this century or it was not. We want to believe there
is some unique way our words hook onto the world and that this
hooking, or accurate representation, makes our statements true or
false. Relativity and quantum mechanics make it hard to maintain
the convention of an absolute word-to-world fit. For example,
relativity, much to the discomfort of some people, shows that the
truth of whose clock is running slower, mine or yours, depends on
the frame of reference from which the statement is made.
Quantum mechanics takes us further from the classical
worldview. We simply cannot say, 'Either the electron goes
through the first slit or it doesn't" if we do not arrange an
experimental apparatus so that we can test this statement.
Furthermore, arranging apparatus in this way precludes displaying
other phenomena such as interference.
In Einstein's words, "This universe of ideas is just as
little independent of the nature of our experiences as clothes
are of the form of the human body." What we say about the world,
our theories, are like garments ' they fit the world to a greater
or lesser degree, but none fit perfectly, and none are right for
every occasion. There seems to be no already-made world, waiting
to be discovered. The fabric of nature, like all fabrics, is
woven by human beings for human purposes.
What does this say about truth? If there can be innumerable
theories of the world, how can there be a unique relationship
between the world and our theories, between the world and what we
say about it? In the conversation of physics, truth is largely
procedural. Physicists are united by a procedure that allows them
to determine the value of a theory. At some point this procedure
involves an appeal to observations that others are free to make
as well. The struggle between Galileo and the Church was a
struggle over the procedure to be used in determining the truth
of certain statements. The resolution of that conflict consisted
in distinguishing two domains of inquiry, religion and science,
each with its own procedure for determining truth. In the realm
of most religions the appeal is to authority; in the realm of
science the appeal is to observations and experiments.
Knowledge of the natural world has been advanced by an
international community of scientists engaged in a common
conversation but one carried out under different rules than most
conversations. As Samuel Ting said, "Science is one of the few
areas of human life where the majority does not rule.' What
scientists have in common is not that they agree on the same
theories, or even that they always agree on the same facts, but
that they agree on the procedures to be followed in testing
theories and establishing facts. Physics is primarily procedural.
Its procedure is to uncover the value of a theory by determining
its consequences and then seeing if these predictions are
confirmed by measurements. A physical theory must make predic-
tions that can either agree with or conflict with observations.
Kepler, for example, abandoned the idea of circular orbits
because predictions made on the basis of circular orbits
conflicted with Tycho's observations. If a theory has no
consequences that might possibly clash with observation, the
theory is not a physical theory but some other sort of theory '
aesthetic, religious, or philosophical.
The language of general relativity replaced the language of
Newtonian gravity in some conversations, because someone
developed a procedure, the eclipse photographs, that allowed the
value of the two ways of speaking to be assessed by bringing
their differing predictions into confrontation with measurement.
Once this confrontation occurred the triumph of relativity seemed
assured. No matter that the overwhelming majority of physicists
were quite convinced that Newton was "right'; Eddington's
observations showed them that Einstein's way of talking about
gravity was a better way of predicting the outcome of certain
experiments than Newton's. Once Eddington had published the
results of his measurements, every other physicist could know the
power of Einstein's language as well.
The value of a theory is not that it fits what physicists
already know but that it points to what they do not know. General
relativity was embraced because it predicted an as-yet unobserved
deflection of starlight. The eightfold way was accepted, not
because it provided a rationale for what was already known, but
because it predicted something not already known, the Omega-minus
particle ' and this prediction was supported by experiment.
To say scientific truth is procedural is not to say that
there is a unique procedure. In fact, there are many procedures.
The point is that the same procedure can be used by anyone else
who has the same questions. If we want to know whether a
particular way of talking about the physical world is valuable,
we look for the predictions the theory makes and compare these
with observations. The measurements of physics must be repeatable
by other physicists in other laboratories. This repeatability,
not the agreement of physicists or the accurate picturing of
nature, makes physics both public and "objective.'
The Unreasonable Success of Physics
If physics is a conversation, and the search for truth
procedural, how can we account for its amazing success? Why can't
we simply say a theory works because it accurately corresponds to
nature in some way ' because the language of the theory
represents the way the world 'really' is? Unfortunately, to say
that nature corresponds to our theories is no more informative
than the explanation provided by Molire's fictional physician
who reassured his patients that morphine works because of its
'dormitive powers.' The problem with a dormitive powers theory is
that it does not tell us any more than we already knew ' morphine
induces sleep.
Mathematics, as Wigner says, is unreasonably effective in
describing the physical world; it is unreasonable precisely
because we can give nothing that would count as a reason. When
Newton's approach failed to lead to an accurate description of
the detailed behavior of Mercury's path around the sun, there was
no way to explain its failure in Newtonian language. Such an
explanation had to await the development of a new vocabulary,
Einstein's general relativity, that could accurately describe
Mercury's behavior. As far as physics is concerned, reasons exist
within the framework of a theory, not outside it. For example, it
makes perfect sense to say that a particular model, such as the
description of the roller coaster, works because friction can be
ignored or because gravity is a conservative field. Newtonian
mechanics provides the framework within which these words func-
tion as explanations.
Explanations that appeal to principles outside a theory tend
to be uninformative. It does not help much for me to say that the
roller-coaster model works because of the additive properties of
the real number system, and it helps not at all to say the model
works because it corresponds to nature. A way of talking about
the world either works in some particular situation or it does
not, but we add nothing to our stock of knowledge by saying its
success or failure is because of correspondence or lack of
correspondence to the world.
How then can we account for the power of Newton's laws,
Maxwell's equations, relativity and quantum mechanics? How can it
be that a few equations are capable of describing the behavior of
systems ranging in size from the atom to the observable universe?
Perhaps, as Weinberg tells us, 'The standard model works so well
simply because all the terms which could make it look different
are . . . extremely small.'.
Einstein addressed the question more broadly. He said, 'The
eternal mystery of the world is its comprehensibility.' This
comprehensibility, our ability to talk about the world in the
language of mathematics, is the blessing that Wigner points out
we neither understand nor deserve. To try to understand, to try
to solve Einstein's mystery and uncover the source of Wigner's
blessing, is to leave the realm of physics and to enter the realm
of metaphysics. A fascinating trip, no doubt, but a journey on
which physics has little to offer by way of illumination. As the
philosopher Ludwig Wittgenstein said, 'What we cannot speak
about, we must pass over in silence.' Einstein described the
nature of physics in the following way:
Physical concepts are free creations of the human mind,
and are not, however it may seem, uniquely determined
by the external world. In our endeavor to understand
reality we are somewhat like a man trying to understand
the mechanism of a closed watch. He sees the face and
the moving hands, even hears it ticking, but he has no
way of opening the case. If he is ingenious he may form
some picture of the mechanism which could be
responsible for all the things he observes, but he may
never be quite sure his picture is the only one which
could explain his observations. He will never be able
to compare his picture with the real mechanism and he
cannot even imagine the possibility of the meaning of
such a comparison [my italics].
Einstein said we cannot compare our theories with the real
world. We can compare predictions from our theory with
observations of the world, but we 'cannot even imagine . . . the
meaning of" comparing our theories with reality.
The Archimedean Perspective
Archimedes was perhaps the greatest of ancient Greek
scientists. Flushed with having developed the mathematical
principle of the lever, Archimedes is said to have exclaimed,
'Give me a place to stand, and I will move the earth.' The idea
of a place outside the world on which to stand has become a
fundamental myth of our culture. This myth has most often taken
the form of a spectator view of knowledge ' the notion we can
stand aside from the action and comment on it from a detached
viewpoint. The epitome of the spectator view of knowledge was
expressed by the eighteenth-century French astronomer
Pierre-Simon Laplace:
We may regard the present state of the universe as the
effect of its past and the cause of its future. An
intellect which at any given moment knew all of the
forces that animate nature and the mutual positions of
the beings that compose it, if this intellect were vast
enough to submit the data to analysis, could condense
into a single formula the movement of the greatest
bodies of the universe and that of the lightest atom:
for such an intellect nothing could be uncertain; and
the future just like the past would be present before
its eyes.
What could be more detached than the spectator who views the
entire universe, past, present, and future, as an object of
contemplation? (Needless to say, for Laplace the scientist has
the perspective of the vast intellect he describes, if only to a
limited extent.) The spectator perspective is an integral part of
the deterministic world portrayed by classical physics.
The idea that we can step outside our systems of
interpretation, our language, and somehow talk sensibly about the
world as it really is seems to be one of the most deep-seated
beliefs we have. The concept reached its scientific zenith in the
triumphs of classical physics. The English physicist and cleric
J. C. Polkinghorne said, 'Classical physics is played out before
an all-seeing eye.' The "all-seeing eye' is a metaphor, so much
so that it never appears to us to be an assumption, but seems
simply to be 'the way things are.' It is this metaphor, acting as
an undisclosed assumption that allows us to talk about how our
theories reflect the way the world really is. That is, it allows
us to
talk about comparing theories with the world. The metaphor of
an all-seeing eye entrances us. As Wittgenstein said, 'A picture
held us captive. And we could not get outside of it, for it lay
in our language, and language seemed to repeat it to us
inexorably.'
End of part two