Schrödinger's Cat and Divine Action:
Some Comments on the use of quantum uncertainty to allow for God's action in
the world.
Robert J. Brecha
Abstract. I present results of recent work in the
field of quantum optics and relate this work to discussions about the theory of
quantum mechanics and God's divine action in the world. Experiments involving
atomic decay, relevant to event uncertainty in quantum mechanics, as well as
experiments aimed at elucidating the so-called Schrödinger's-cat
paradox, help clarify apparent ambiguities or paradoxes that I believe are at
the heart of renewed attempts to locate God within our constructed physical
theories and tend to narrow the gaps proposed as an opening for divine action.
Some problems arise because of imprecise use of nonmathematical language to
force quantum mechanics into an intuitive "classical" framework.
Keywords: determinism; divine action; measurement; quantum chaos;
quantum mechanics; realism; Schrödinger's cat.
quoted from: Zygon, vol. 37, no. 4 (December 2002),
pp.909-924
In discussions about the possible
modes of interaction between religion and science, reference is often made to
physical theories of the twentieth century and ways in which these theories may
open new avenues for achieving a closer integration between the two
disciplines. Theologians, as well as some physicists, have begun to explore in
greater detail, and in the spirit of serious dialogue, the extent to which the
"battle" between science and religion may have been the result of
misunderstanding on both sides. It is probably the case that this discussion
has been reawakened only fairly recently because of what would appear to be the
final death of the two great demons of classical physics, those of Pierre Simon
Laplace and James Clerk Maxwell. In the spirit of Enlightenment rationalism,
physicist and mathematician Laplace made the somewhat presumptuous conjecture
that it would be possible in principle for a hypothetical being to apply
mathematical and physical principles to any system in such a way that one would
be able to predict future developments with arbitrary accuracy for arbitrarily
long periods of time. That Laplace himself apparently felt that his omniscient
demon could be none other than God did not prevent his idea from being used
thereafter by both scientists and theologians as a starting point for claiming
a complete separation of their respective fields.
My purpose in this article is to
examine one specific aspect of the revived dialogue between religion and
science. Many scholars have used concepts from the theory of quantum mechanics
to provide an example of how God's divine action in the world might be
formulated so as to be consistent with physical theory. According to this
bottom-up model, the inherent ontological indeterminacy seemingly required by
our best present-day understanding of quantum mechanics can be seen as
equivalent to saying that "God is the hidden variable" (Murphy 1997,
342). Thus, God can make choices about the detailed behavior of quantum
systems, as long as the outcome is consistent with probabilities as calculated
using the mathematical tools of quantum mechanics, and still not be seen as
interventionist. I present what I hope is a concrete contribution to this
discussion by emphasizing results of some relevant recent experiments in the
field of quantum optics.1 These do not prove any one view of quantum
mechanics but rather show that the approach taken by physicists to the open
questions of a physical theory is to do experiments and refine the mathematical
theory. The outcome, as has almost always been the case in the past, is to
close down further the gaps proposed as an opening for divine action. Expressed
in a slightly different way, the general result of the experiments described
here is to clarify what sometimes seem to be ambiguities, or paradoxes. These
perceived ambiguities are what I believe to be at the heart of renewed attempts
to locate God within a constructed physical theory such as quantum mechanics. I
present as well a short discussion of some recent experiments aimed at
understanding quantum chaos, which in some ill-defined way sits on the boundary
between the quantum and nonlinear worlds and therefore has in the past been
taken to be relevant to the divine-action arguments.
A few preliminary comments are in
order. Most authors writing about divine action and quantum mechanics start
from a realist metaphysical perspective. In a recent article in Zygon, Gregory
Peterson raises the important point that the ontological status of physical
laws is a too-often-neglected subject for consideration in discussions between
scientists and theologians (Peterson 2000, 884). It seems to me that there are
at least two possible directions in which we could go if we were to take a step
away from believing in the strict realism of quantum mechanics. Peterson
believes that we can approach the question of divine action very differently if
we consider the laws of physics to be only approximations or to represent only
statistical regularities, since there would be no sense in which God must be
contravening inviolable laws of physics. A second possibility is to give up
realism, critical or otherwise, as a criterion for physical law, because then
we could ask more fundamentally about the necessity of even worrying about
divine action in connection with a specific mathematical construct that we
happen to be using at this point in history to try to understand our physical
world. Peterson mentions the point about realism as an aside in his article,
but I believe that he has touched on an extremely important topic that must be
given further consideration. I find some of the ideas on this topic expressed
by William Stoeger (1993) very stimulating.
The above comments are not to be
taken as a sign that I endorse a naive instrumentalism with respect to quantum
mechanics. One can find much of value in, for example, the works of Pierre
Duhem, although he was writing before the advent of quantum mechanics. Some of
the more modern adherents to variations of the ideas of Duhem include Bas van
Fraassen (1980) and Nancy Cartwright (1983). These philosophers of science do
not address the conversation between theologians and scientists, but their work
is of at least indirect relevance as it addresses the important questions of
realism and, especially in the case of Cartwright, of what physicists actually
do when they use quantum mechanics as a tool. To sum up, because most of the
contributions to the debate about possible room in quantum mechanics for divine
action depend implicitly on some version of realism being attributed to the
theory, the metaphysical foundation should be firm enough to support the whole
edifice.
Although I will be looking at the
arguments as a physicist and from outside the theological tradition, it is of
course possible to view attempts to unify quantum mechanics and divine action
from the point of view of theology as well. In recent issues of Zygon there
are several articles that discuss the theological problems relating to these
attempts. Nicholas Saunders (2000) gives a valuable overview of some of the
most prominent proposals that have been circulated by scholars in this field.
He points out that theologians must implicitly arrive at the orthodox
interpretation of quantum mechanics, involving the collapse of the
wavefunction, to retain the ontological uncertainty necessary to have divine
action without interventionism. Alternative versions of quantum mechanics, such
as David Bohm's pilot waves or Hugh Everett's many-worlds interpretation, are
specifically designed to circumvent the perceived problem of a probabilistic
theory. Given standard quantum mechanics as a starting point, the question
becomes to some extent a matter of degree: Does God act in all quantum events
or only in some critical events that bear macroscopic consequences? In the
first case, it seems difficult to avoid a charge of occasionalism.
If one grants some sort of
realism to fundamental physical theories and in the case of quantum mechanics
accepts uncertainty as a key part of the theory, then a God acting in every
quantum event could be accused as well of only keeping up a facade of
indeterminacy to fool scientists while actually operating by very different
methods. As has often been pointed out, the problem of the existence of evil
looms large with this approach. Further, this seems to be a risky path to
follow for at least one other reason not usually mentioned, namely, that this
line of reasoning begins to sound perilously like that used by creationists who
claim that God created geological structures in six days but in such a way as
to simulate a 4-billion-year history of Earth.
If, on the other hand, one allows
God to act only infrequently, for example during a measurement, it is difficult
to avoid the charge of interventionism. The claim of divine action during the
act of quantum measurement is difficult to even define, because most
measurements in quantum systems are not of the type in which one opens a box to
see if Schrodinger's cat is alive, dead, or a bit of each. As I discuss below, quantum
measurement really means any interaction of a quantum system with its
surroundings. Thus, because quantum mechanical processes such as collisions
between atoms are taking place all the time, separating occasional measurements
from continuous action seems problematic.
Another example of a theological
approach is given by Steven Crain (1997), who has considered the use of
"special divine action" in the work of John Polkinghorne. He
concludes, in essence, that belief in a transcendent God renders highly
suspicious any attempt to require that God must exploit built-in features of
the world as a means for carrying out actions. Thus, the only proper solution
is to separate the two domains of natural science and theology. Theology is then
classed with metaphysics and is thus not part of the world open to scientific
investigation. On the other hand, Crain does recognize that theology "must
address the world as best we understand it" (1997, 50), that is, that
developments in science must be taken into account in any practical theology.
This point is, of course, implicit in nearly all Zygon articles.
I have one final comment before I
present specific examples from current research in quantum optics. It is often
claimed that the "new physics" is much less amenable to an intuitive
understanding than was classical physics. For example, Polkinghorne has written
that "the counterintuitive character of the quantum world . . . results in
its discovery having caused the most radical revision of physical thinking
since the start of modern science" (Polkinghorne 1991, 85). The belief
that a physical theory is nonintuitive or even counterintuitive can lead to
extreme claims about the latitude allowed in interpreting that theory. The
significance of the lack of intuition about systems governed by quantum
mechanics (or chaotic dynamics or special relativity) is extremely
questionable. One of the most difficult tasks pedagogically in a first-semester
physics course is to find ways of convincing students to accept and internalize
ideas that are now three hundred years old. For example, it is still the case
that one can be satisfied at the end of a semester if a significant fraction of
introductory-level physics students can be considered Newtonian thinkers. That
is, the ideas most of us bring into a physics course, and that many students
have even after a course, are much closer to the physics of Aristotle (I
am thinking here of the concept of inertia and the "natural" state of
motion of a body, for example), which seems more intuitive. The non-intuitive
nature of modern physics as compared to Newtonian mechanics is most likely
irrelevant to the current discussion.
quantum
mechanics and quantum optics experiments
Using Paul Dirac's classic
quantum mechanics text as a starting point, Carl Helrich gives an excellent
description of some of the basic principles of quantum mechanics in a recent
issue of Zygon (Helrich 2000). He includes definitions of quantum
mechanical versus classical states as well as discussions of the Heisenberg
uncertainty principle in terms of abstract mathematical operators and of the
deterministic nature of the Schrodinger equation. In what follows I repeat for
emphasis a few of these points and amplify others that I feel are sometimes not
appreciated enough. Helrich concludes that there is nothing in the formulation
of quantum mechanics that leaves enough uncertainty for divine action within
the theory. He argues further that imposing the limits of one of our current
theories on God's action is in effect an impoverishment of the concept of an
omnipotent deity (although this tactic has been used often in the
religion-and-science dialogue).
If we begin by assuming some
interaction between God and the world, mediated by physical theory, in what sense
can we postulate that there is room within quantum mechanical nature for divine
action? I describe a few features of the theory that seem relevant, since these
have been previously linked to possible modes for understanding divine action
in the world and illustrate how experimental and theoretical research continues
to make more precise our understanding of these features of quantum mechanics.
Schrodinger's Cat. A first example of the alleged strangeness
that comes with quantum mechanics is provided by the mystery of Schrodinger's
cat. This oft-cited paradox involves one of the fundamental features of quantum
mechanics, called "superposition states." In classical physics, as
well as in everyday experience, we know that a particle, or a person, is either
"here" or "there." If we do not have enough information
about the motion of the particle (or, in the more usual case, if the system
consists of many parts and is thus too complicated to describe exactly), we may
haveto assign probabilities to various locations. According to quantum
mechanics, it is possible for a system to exist in a superposition, the state
"here and there." This phenomenon is deeply ingrained in the
mathematical structure of quantum mechanics and, furthermore, has in many cases
observable consequences. That is, predictions that rely on the existence of
superpositions can be tested.
Schrodinger's cat has been the
guinea pig (to mix metaphors) in the world of quantum mechanics thought
experiments for more than seventy years. The cat is assumed to be in a box with
a demonic device that triggers its death with 50 percent probability in a given
time. The statement of the paradox, as usually presented, is that quantum
mechanics would predict that the cat is in a state of "half-alive + half-dead"
(a superposition) and that the quantum mechanical "collapse" into one
of the definite outcomes is produced only when an observer opens the box to
make a "measurement." This example has been used so often at least in
part because the proposition sounds so absurd. I have the sense that the net
result of many discussions about Schrodinger's cat is to leave an impression
that physicists are in a fog about what to do with their theory. The serious
question to be asked before trying to interpret this thought experiment in
light of arguments for divine action is the following: If quantum mechanics
allows superposition states to exist, why do we never see them in the
macroscopic world?
One feature of the paradox that
seems to me to be irrelevant is that of amplification. Some wish to extend a
metaphor for Schrodinger's cat to other systems by attaching great significance
to the fact that the decay of the single radioactive atom can be amplified to
result in the death of the cat or, more generally, the change in state of a
macroscopic system. The triggering of a large effect by one small push can be
described just as well by classical physics as by quantum mechanics. One need
think only of the tiniest perturbation needed in the mountains to release an
avalanche, for example. In this same spirit, some authors wish to move events
of the quantum regime into the field of biology, by claiming that an individual
quantum event (i.e., one X-ray photon incident on a DNA molecule) can create a
mutation and thus determine the fate of an individual through altered genetic
characteristics (Russell 1998b). Although I certainly do not deny that these
processes occur, it does not appear to me that the events are in this case
different in kind from normal classical accidents that can have large
consequences. A person seriously injured or killed in an automobile accident, a
very classical event from the point of view of physical theory, has a very
different further development than would have otherwise been the case. From the
point of view of quantum physics, a DNA molecule is already an almost
hopelessly large, complicated, and classical object. Although one may speak of
divine action in such a case, it must certainly be of the interventionist type
and not through the framework of quantum theory.
I turn now to current attempts to
understand the problem of Schrodinger's cat. The solution can on the one hand
be stated almost trivially: quantum mechanics, although applicable in principle
to any system, deals best with small systems; whatever "small" means
exactly, a cat does not qualify. Quantum mechanics is formulated to deal with
microscopic systems, and one must be careful when using quantum mechanical
language to describe macroscopic systems if one wishes to avoid apparent
paradoxes. Thus, before becoming too disturbed by the thought of a cat that is
half dead and half alive, we must ask whether we are treating the cat
rigorously according to the rules of quantum mechanics, since we are trying to
talk about a mathematically modeled physical system. The clue that caution is
advisable is that, once we sit down with pencil and paper, we do not have the
slightest idea how to write the Schrodinger wavefunction for a cat.
A more detailed explanation of
the paradox involves the concept of decoherence, which is essentially a
description of how (microscopic) quantum systems interact with their
(macroscopic) surroundings. This is an area of current active research, but not
in the sense of making modifications to quantum mechanics so as to make the
theory more intuitive or "classical." The idea of decoherence adds
nothing new to the mathematical framework of quantum mechanics itself; rather,
it is a more careful consideration of complicated combinations of systems. From
this point of view, the resolution of the paradox of Schrodinger's cat is
simply an example of how scientific theories are developed further with time,
testing and solving their own problems.
In recent issues of Zygon, the
concept of decoherence has been implicitly touched upon more than once. Thomas
Tracy mentions the important point that decoherence essentially implies that
quantum measurements are taking place continuously, and he quotes Robert John
Russell to this effect (Tracy 2000, 897). The point of the reference to decoherence,
as I see it, is that it tends to blur the distinction between occasional acts
of divine action through measurements (which we tend to picture as a very
intentional act) and the continuous divine action present in every quantum
interaction. Decoherence tells us that measurements are nothing more than
interactions of any sort whatsoever. I now briefly summarize the approach used
in some recent experiments to investigate this more quantitatively.
Physicists do not typically work
with cats in the laboratory, and a cat is in any case far too complicated to be
considered useful for an experiment in quantum optics, so it is necessary to
find a reasonable substitute. The requirement is that one have a quantum system
(here a single atom, corresponding to the radioactive atom in the original
proposal) coupled to a classical measuring device (the cat). In beautiful
recent experiments ontwo different model systems (Brune et al. 1996; Myatt et
al. 2000), the principle of creating a model Schrodinger's cat and of demonstrating
decoherence has been tested, and observations have been made illuminating how
the rules of quantum mechanics describe very well the coupling between systems.
In the experiments of M. Brune and his colleagues, the microscopic system is a
single atom of rubidium with only two pertinent energy levels. The two states
of the atom correspond in the original thought experiment to the radioactive
atom's having either decayed or not decayed. The measuring device
("cat") is the electromagnetic field in a nearly perfect box
(superconducting cavity); the size of this field could be varied, as could the
strength of the coupling to the rubidium atoms, in such a way that it was
possible to move from a quantum to a classical measurement interaction.
At first sight this may not sound
like the same problem that has been discussed in most contributions on the
implications of quantum mechanics, but I would contend that this system, or
that of C. J. Myatt and colleagues, is of exactly the type that we should be
considering. These experiments are constructed such that it is possible to
follow how decoherence takes place as the measuring device becomes larger (and
thus more classical) and to shed light on the reason why we do not see
superpositions of macroscopic systems in nature.
To summarize the results of the
experiments, we do not ever see the kind of macroscopic coherences described by
the dead cat/live cat example simply because there are so many quantum
interactions going on that these absurd possibilities get washed out. If, as in
the experiments described here, it is possible to make the classical measuring
device (the "cat") small enough and to then change its size in a
controllable way, one can investigate exactly how quickly the disappearance of
macroscopic superpositions occurs.2 These experiments shed light on
how small quantum systems become classical ones, at least in part because of
interactions with their surroundings. That is, one can explore the boundaries
between classical and quantum physics in a very controllable fashion.
Radioactive Decay and
Spontaneous Emission. Another
tactic for allowing divine action into quantum mechanics involves events such
as the radioactive decay of a nucleus or the spontaneous emission of light from
an atom or molecule.3 In either of these cases there is a randomness
built into the system: it is possible to calculate the probability that a
nucleus or atom will decay within a given time (or, equivalently to predict
that of a collection of such objects a certain number will decay in a given
time), but we are prohibited from knowing, even in principle, exactly when an
event will occur or exactly which atom or nucleus will decay. Again, the laws
of quantum mechanics give us information only about probabilities, not about
specific events.
As one example, Nancey Murphy
offers an argument for God's divine action based in part on the view that the
microscopic quantum world operates without sufficient reason for a specific
event to occur. In her typology she asks if the when for a quantum event
taking place is (1) completely random, (2) internally determined, (3)
externally determined, or (4) determined by God (Murphy 1997, 341). Option 1
she rules out primarily because she likes option 4 better, given a choice.
Options 2 and 3 are ruled out because Murphy thinks that the current status of
quantum mechanics, in which Bell's theorem and the Clauser-Aspect experiments
(both described in the next section) have ruled out local hidden variable
theories, does not allow for either internal or external sufficient causes for
a quantum event.
I believe that this reading of
the situation is somewhat too stringent. The following, although it does not
provide a complete solution, at least opens up the question again. Consider,
for example, an atom that has been excited to a quantum energy level above its
lowest, or ground, state.4 We can think of a fluorescent light in
which mercury atoms are excited by impacts with electrons and then give off the
visible-light photons we see when they decay again to the lowest energy level.
Are these decay processes really random? That is what quantum mechanics seems
to tell us. Are they without a cause? I would claim that quantum mechanics does
not tell us exactly this. The cause of the decay of an excited-state atom is
its interaction with the surroundings, or, to quote Murphy (1997, 341), it is
"externally determined by the entity's relations to something else in the
physical system." In the case described, the surroundings are the quantum
vacuum, which is not at all a vacuum in the Aristotelian sense of a totally
empty void. In quantum field theory the vacuum is an active place; although it
has zero average energy, the fluctuations about zero are all-important.
Polkinghorne has pointed out,
albeit in a different context,5
Classically the vacuum is just
emptiness, nothing there, nothing happening. Heisenberg does not allow a
quantum vacuum to be so inert. Each possible state of matter—photons,
electrons, each different sort of quark, and so on—is described by a quantum
field. The state in which all of these fields have their lowest energy is the
vacuum, rock bottom. There are then no photons, electrons, quarks, etc,
present, but that does not mean that nothing is going on. Quite the contrary,
for the vacuum in quantum theory is a humming hive of activity. . . .
Heisenberg demands that the lowest energy state . . . involves a slight
quivering. . . . This quivering is the zero point motion. Augmented to the
complexity of a quantum field it produces the fluctuating vacuum that I have
described. (Polkinghorne 1986, 67)
Polkinghorne's vivid description
of the quantum vacuum reflects accurately the surroundings of every atom in a
fluorescent bulb. The atom constantly "feels" these fluctuations in energy,
and the resulting interaction is behind the observed fact that the atom
eventually drops from the higher to a lower energy level. Thus, when Murphy
(and others as well) talk about quantum events as "just happening,"
there is a sense of completely acausal randomness that is exaggerated.
To take this example one step
further and perhaps lend a greater plausibility to the idea that the
surroundings of an object, although referred to as the vacuum, can be the cause
of a quantum event, I will describe briefly some experiments in which the
quantum vacuum was altered in a controlled way such that the effects on a
single atom could be observed. To understand the experiments, consider an atom
that has energy levels such that it emits green light of wavelength 500 nm6
when in a fluorescent tube. If we place this atom in a cubical metal box, 200
nm on a side (I skip all details about how this might be done or why it should
be a metal box), we predict from quantum theory and confirm by experiment that
this atom now does not emit light at all but remains in its excited state
indefinitely. The rough reasoning behind this phenomenon is that our box is too
small for a (half) wavelength of the light to "fit" inside, and
therefore the atom is "stuck" in its excited state until we give it
more room ("modes") into which it can emit. That is, the
contributions of the vacuum field at those wavelengths, which would normally be
present in free space, are also not allowed in the box and thus cannot cause
the atom to change states. The experiments performed by various groups to test
this idea (Serge Haroche and Daniel Kleppner [1989] give a good introduction)
demonstrate the principle clearly, although, as usual, some idealizations are
involved in translating the theoretical language into an experimental setup.
Although we still cannot predict
when the atom will emit its photon except probabilistically, it seems to me
that the cause of the decay in a general sense has been shown by the experiment
described above. By performing this experimental manipulation it is possible to
vary the rate at which atoms emit light. Thus, some of the mystery of the
spontaneous emission of light (or, by a similar argument, of the radioactive
decay of a nucleus) is removed. Certainly one of the points about quantum
mechanics that sounds so strange as it is often presented in a brief synopsis
is that events "just happen" for no apparent reason. That seems to me
to be an oversimplified view of the quantum world.
Bell's Theorem and the
Einstein-Podolsky-Rosen Paradox. It is sometimes argued that the surprisingly large (from the point
of view of classical physics) correlations between quantum objects that
separate after starting out as parts of a composite system means that there is
a holism in nature, allowed for by quantum mechanics and denied by
reductionist, Newtonian physics. Furthermore, it has been surmised that this
holism could be made consistent with the possibility of divine action (Russell
1998a). An important example is given by the Einstein-Podolsky-Rosen Gedankenexperiment,
as modified by Bohm. When two photons are emitted sequentially by the same
atom, as can be arranged experimentally, and when one sets up a carefully
prescribed set of measurements (Freedman and Clauser 1972; Aspect, Grangier,
and Roger 1982), the correlations7 found in measurements made on the
properties of the two light particles are not what one would expect from a
classical theory but do confirm the predictions of the standard quantum
mechanical theory (Bell 1964). Most important, the results are in direct
conflict with the so-called local-hidden-variables formulation of quantum
mechanics, in which attempts have been made to derive quantum mechanical
results equivalent to the successful Schrodinger equation, but without the
accompanying probabilistic interpretation. Thus, in a situation for which
quantum mechanics explicitly predicts an outcome at variance with our classical
"intuition," the quantum mechanical result has been clearly shown to
give the correct answer.
One mitigating factor to keep in
mind when considering the seemingly mysterious character of the correlations
predicted by quantum mechanics, and an explanation of why such effects do not
seem to appear in everyday life, lies in the extreme difficulty of trying to
prepare an experiment that realizes the concrete predictions of Bell and
standard quantum mechanics as opposed to alternative theories. It is very
challenging to create quantum mechanical systems isolated enough from their
surroundings that such effects may be observed. This relates as well to the
arguments I used above when discussing Schrodinger's cat; it is easy to find
strange predictions if one jumps from the basic principles of quantum mechanics
to systems that effectively cannot be treated rigorously within the theoretical
framework. Further, one should be hesitant to jump from the fact that quantum
mechanically predicted correlations are found in repeated measurements made on
individual pairs of photons, separated by lengths of optical fiber in a laboratory
containing hundreds of thousands of dollars' worth of equipment devoted to the
task, to sweeping generalizations about the holism found in nature based on
that theory. No macroscopic system would display the properties described by
Bell's theorem, for reasons related to decoherence, as described earlier.
Russell (1988a) has discussed at
length some of the implications of Bell's theorem for philosophical and
theological appropriation of quantum mechanics. In the end, however, he relies
on a metaphorical approach to relating quantum mechanics and divine action.
This is certainly one possible tactic, but then I would argue that the goal for
relating divine action to specific scientific theories has been changed
greatly. Metaphors and models are not the basis of a theory such as quantum
mechanics, but rather they serve as a tentative guide as to how one may apply a
theory in a given situation. Comparing models in physics, which typically serve
as guides for setting up mathematical problems, with metaphors and models in
theology would seem to be a very difficult task.
In this context I now consider a
quote from Russell regarding quantum mechanics. He writes, "Another area
to which the gossamer-like quality of quantum correlations might be relevant is
inter-religious unity. . . quantum correlations offer stimulating metaphors for
our unity in Christ and our search for wider ecumenical unity in the global
religious perspective. Moreover the insights from quantum physics can be
extended as well to the constructive theological agenda." (Russell 1988,
358)
I contend that examples such as
these illustrate the danger of using metaphorical language in one area of
intellectual pursuit, based on the very concrete usage of language in another.
If we read this passage and then think about how extremely difficult it is to
maintain quantum correlations and how easily they can be destroyed, not to
mention the fact that almost any experiment designed to observe quantum
mechanical effects requires highly artificial conditions in elaborate
laboratory surroundings, the positive metaphor can be turned around to make the
quest seem like a hopeless pursuit. Theological metaphors based on the
precisely defined formalism of a physical theory appear to me to be far removed
from the point where the intricacies of the theory are relevant.
quantum
chaos
Some hope has been expressed in
the conversation between scientists and theologians that a theory of quantum
chaos might help to clear up some of the interpretational difficulties encountered
in discussions of divine action as possibly allowed by nonlinear dynamics or
quantum mechanics. As the name implies, quantum chaos could be considered to
provide a bridge between the world of quantum mechanics and the world of
chaotic behavior in nonlinear dynamical systems.8 It should be
noted, however, that it is difficult even to define precisely what we mean by
quantum chaos.
I will look at one possible
approach, namely, that a given classically described system sometimes has an
analogous quantum mechanical system for which an experiment can be envisioned.
Although there are problems with making this analogy, it seems to be the best
we can attempt at this time. Unfortunately, investigations on such systems
carried out thus far seem to rule out any such quantum chaos. In a recent issue
of Zygon, Jeffrey Koperski (2000) presents an overview of the problems
encountered when using the idea of chaotic quantum determinism as an avenue for
allowing divine action. His conclusion is that the link between quantum
mechanics and chaotic dynamics is simply too unclear, and perhaps even too
contradictory, for us to appropriate these concepts theologically as the causal
joint for divine action.
In the spirit of the experimental
results I presented above, I show here how physicists have made progress in the
past few years in performing experiments aimed at finding signs of what might
be considered quantum chaos (Ammann et al. 1998; Moore et al. 1995; Klappauf et
al. 1998). These results temper somewhat Koperski's statement that a retreat
has been made from the search for a correspondence between the quantum
andchaotic realms. The classical system being modeled is a "kicked
rotor," which is essentially a swinging pendulum that is periodically
given a sharp push. It can be shown experimentally and theoretically that this
kicked rotor can exhibit chaotic behavior. In the recent experiments, the
starting point is a "quantum" system consisting of a sample of atoms
confined to a small area by laser light, which can be arranged such that the
atoms slosh back and forth slightly. Interactions are arranged to be analogous
to a classical system, that is, the group of atoms is periodically given a
"kick" in the form of a pulse of laser light. Monitoring the
experimental quantities that show the signature of chaos in the classical
system, the experimenters find no sign of chaotic behavior in the quantum
system. They take this experiment one step further, however, in that they use
the concept of decoherence, as described above, and make the system
progressively more classical by coupling it to its surroundings. As they
increase the amount of classicalizing interaction, they find that the
experimental signature of chaotic behavior gradually begins to appear.
The experiments described here do
not demonstrate in a definitive way that there is no quantum chaos, nor that
the physicists involved have disproved any particular hypothesis, either about
quantum chaos or about divine action, but simply that the ideas of both quantum
mechanics and nonlinear dynamics, being physical and mathematical theories, are
testable. It is only through such testing, and through the usual interaction
between experiment and theory that is the strength of scientific research, that
we can make any sense of the sciences. On the other hand, we must say as well
that the results of the experiments described above leave an important question
for further investigation. If quantum mechanics is to be considered the prime
theory for the description of matter, and if it is supposed to lead to
classical Newtonian mechanics in some limit to be defined carefully, then where
is the bridge located if not in a system such as the kicked rotor that can be
approximated physically in both its quantum mechanical and classical versions?
conclusions
I have presented a summary of
some of the most recent experimental results that to my mind have some bearing
on the questions raised in the discussion of divine action in the world as it
relates to interpretations based on a specific physical theory. I believe that
progress in experimental testing and understanding of these theories is such
that attempts on the part of theologians to appropriate these theoretical
frameworks to provide an avenue for divine action run the risk of the fate of
earlier God-of-the-gaps arguments. Many of the apparent paradoxes that arise in
interpretations of quantum mechanics result from imprecise use of
nonmathematical language to try to force quantum mechanics into an
"intuitive" classical framework. This points to the danger in using
classical analogies when discussingsystems that can be described only with the
more fundamental theory of quantum mechanics; conversely, when discussing
macroscopic systems (such as cats), we must be certain that we account fully
for all parts of the system if we wish to avoid paradoxical results. Some of
these points have been fully realized by physicists and formulated carefully
only within the last several years (Omnes 1994). Finally, it seems to me to be
an even riskier strategy to use analogies and metaphors based on precise
mathematical theories as justification for a theological construction of divine
action.
If one wishes to relate quantum
mechanics to another subject area, it is not a good strategy to do so by
starting with an example (a live cat) that no physicist would ever consider
trying to treat using the formalism of quantum mechanics. On the other hand, to
start with a system that is well understood, such as a single rubidium atom,
and to couple it in an experiment to another very simple, well-characterized
system (an electromagnetic field of one single frequency, with a well-defined
amplitude), and to then monitor what happens to this system and compare the
results to those predicted by quantum mechanics (which in this case gives
relatively simple, analytically computable answers) shows that the theory is
perhaps not quite as mysterious as it might seem. In addition to the
experiments I have described here, there are other recent investigations into
the nature of the wave-particle duality as well as active research into the
properties of quantum statistical systems consisting of bosons or fermions or
mixtures of both. These latter themes have also been the subject of discussions
between scientists and theologians but could have been included with the cases
presented above, with similar arguments being made.
Finally, another point discussed
only briefly above but one that deserves more careful attention is that the
critical realist view upon which any such project must be based can also be
persuasively criticized, thus undermining the goals of making a close linkage
between divine action and specific physical theories.9 It is
encouraging that the dialogue between scientists and theologians has begun
again, and seemingly on a different level of mutual respect. However, it does
justice to neither side to overlook the limitations and strengths of the other
by trying to inappropriately borrow ideas meant to serve in a bounded sphere of
inquiry.
NOTES
1.
Quantum optics is a specialized branch of physics that can be characterized as
dealing with the interaction of light and matter on a scale at which effects
predicted by quantum mechanics become important. It is probably one
of the most active arenas for testing basic quantum mechanical theory.
2. Omnes
provides several calculated examples (Omnes 1994, 323). For example, a
particle the size of a large molecule (10 nm) interacting with the few atoms in
a good laboratory vacuum (106 molecules/cm3) experiences
decoherence due to collisional interactions in a time on the order of 10-17
seconds, far too short to be measured in any conceivable experiment.
3. We
are all at least vaguely familiar with the concept of radioactive decay;
spontaneous emission is probably seen much more often, however.
Every time we switch on a fluorescentlight, electrical current transfers energy
to atoms in the fluorescent tube. After a very short time, these same atoms
give off that energy in the form of light.
4. In
spite of the fact that the Bohr model of the atom has been replaced by the
quantum mechanical description, it is useful to think of atoms as little
planetlike systems in which the radius of an electron "orbit"
corresponds to the total energy (kinetic plus potential) of the electron as
described here. When farther away from the nucleus, the electron has more
energy; when closer, less energy. A change in total energy,
corresponding to a jump between one orbit and another, occurs together with the
absorption (going to a larger orbit) or emission (dropping to a smaller orbit)
of a quantum of energy. Each state of the atom corresponds to one
electron orbit.
5. In
this case, that a quantum mechanical version of the creation of the universe
resulting from a fluctuation of energy in the quantum vacuum could not be
considered creation from nothing (creatio ex nihilo} because this
quantum vacuum is a real entity.
6. The
unit nm is a nanometer, or billionth of a meter. Considering light as a wave,
blue light corresponds to a wavelength of 400 nm, and red light has a
wavelength of about 650 nm.
7. The
correlations are measurements made on one particle and compared to those made
on the second light particle. We see that in a series of measurements,
half the time particle 1 has a clockwise spin and half the time a
counterclockwise spin, and likewise for particle 2. It is only when
correlating the individual measurements according to the formula presented by
Bell that we can make the comparison required to distinguish classical and
quantum predictions.
8. For a
nice introduction to this topic, especially as it relates to the
religion-and-science dialogue, see Wildman and Russell 1997.
9. I
would like to thank the members of the Religion and Science faculty seminar at
the University of Dayton for stimulating discussions; Mike Barnes, Dan Fouke,
Therese Lysaught, and Jim Heft merit special thanks. In addition, I
have had many valuable conversations with John Inglis, Leno Pedrotti, and Bruce
Craver and thank them for their patience and willingness to engage in these
discussions.
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Robert J. Brecha is Associate
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45469-2314. Work on this article was supported in part through the Religion and
Science Faculty Seminar at the University of Dayton, Spring 2000.
