Stephen M. Barr's "Faith and Quantum Theory" (March) gives an accurate portrayal of quantum theory as far as it goes. Barr, however, writes off David Bohm's approach to the subject by arguing that it "brings back Newtonian determinism and mechanism." Such an argument is fallacious, because Bohm's theory gives rise to nonlocal phenomena. By nonlocal, we mean that an event at point A can be correlated with an event at point B with no discernable connection between them.
Even in the classical Newtonian realm, the deterministic system of Laplace is impossible except, perhaps, with a very small number of interacting particles. For systems with very large numbers of interacting atoms and molecules, collective phenomena prevent any kind of prediction or, indeed, retrodiction. Such collective behavior was first studied by Poincare more than a century ago. The research stagnated until the advent of computers, which were needed to study the evolution of instabilities that announce the onset of chaos (in the scientific sense) and self-ordering. The onset of such instabilities is the cause of our inability to predict reliably the weather more than about a week in advance.
Robert C. Whitten
Stephen Barr explains that Peter E. Hodgson posits the Bohmian theory as the "only metaphysically sound alternative" with respect to interpretations of quantum theory. I like the fact that its being "metaphysically sound" is Hodgson's criterion for judging the veracity of the theory. And Barr seems to hold to the same criterion. With respect to the common themes and questions of traditional metaphysics, however, I was wondering if Barr would be able to explain in greater detail why he prefers the traditional Copenhagen interpretation of quantum theory.
Stephen Barr voices his opposition to determinism in favor of the Copenhagen interpretation of Heisenberg's uncertainty principle, finding it sympathetic to biblical faith. Yet other religious scientists reject the Copenhagen interpretation, as Barr notes: "Hodgson insists that Bohmian theory is the only metaphysically sound alternative. He is unfazed that it brings back Newtonian determinism and mechanism."
Inasmuch as Barr holds that Christian orthodoxy requires the affirmation of free will, he stands on solid ground. That same affirmation, however, doesn't bolster any purely scientific argument in favor of the Copenhagen interpretation. Consistent with modern science's limits, Hodgson rightly observes that "physics can take no account of Divine intervention or of acts of free will, so in the course of scientific research the world is assumed to be strictly determined" (Science and Belief in the Nuclear Age). Hodgson goes on to explain that "God causes everything, but He also acts by secondary causality when he creates matter and gives it certain definite properties. Thereafter the matter behaves in accord with these properties. This does not happen by unbreakable necessity, because God has complete power over nature and can suspend or alter the laws of nature.... This means that Laplacian determinism is unacceptable.... [B]oth God and human beings can cause ... effects" that Laplacian determinism cannot explain.
If it were true that physical laws are absolutely inviolable, the natural order would seem to preclude miracles. Yet perfectly reasonable believers such as Hodgson and St. Thomas Aquinas affirm unequivocally the reality of miracles.
Despite Barr's earlier essay "The Miracle of Evolution" (February 2006), it isn't entirely clear whether he would admit without qualification the reality of miracles. If he does, then why wouldn't he accept the idea that physical laws may be broken through the insertion of human acts?
I would encourage believers to take Hodgson's work more seriously than they might otherwise do if they relied exclusively on the passing acknowledgement found in "Faith and Quantum Theory." (One should note that the back cover of Hodgson's Science and Belief contains several glowing recommendations, including one by Barr himself.)
Peter A. Pagan
While Stephen Barr is to be commended for his attempt to deal in a short essay with the complicated subject of the implications of quantum theory for religious belief, his article contains several misstatements that weaken and to some extent deflect his argument.
(1) His claim that Planck proposed that light energy travels in little packets, now called photons, is historically incorrect. Planck proposed only that resonators in the solid body in equilibrium with the light absorbed light energy in discrete units. It was Einstein who proposed that this discreteness resided in light radiation itself, an interpretation that Planck opposed for many years afterward.
(2) Barr's interpretation of a light particle passing through two windows at once is not the presently accepted one. In some sense, a photon passing through one window "knows" the other window is there and acts accordingly. An extensive literature of theory and experiment has been built up by elaborating on this insight. In one example, it has been shown that a photon already heading toward the two windows can anticipate the experimenter pulling down the shade on one of them and act accordingly. These considerations point to a much stronger interaction of observer with observed than Barr posits. An answer to some of the philosophical questions Barr raises will require a deep probing of this interaction, without an a priori dismissal of the question as to what extent "minds create reality."
In making the statements in the preceding paragraph, I have dismissed alternatives, such as Bohm's pilot-wave theory, as being without experimental justification. Also, I am a bit surprised that Barr did not mention string theory as an alternative school of thought, even though it has become quite controversial lately.
(3) Barr seems to rely too heavily on Heinz Pagels' dismissal of Buddhist philosophy. While either classical mechanics or modern physics can be the basis of the encounter, much of the recent debate between science and Buddhist thought does revolve around quantum theory, as in the dialogue between Matthieu Ricard and Trinh Xuan Thuan in The Quantum and the Lotus. The interconnectedness of all phenomena and the role of the observer in any observation (which includes the question of the relation of matter and consciousness) can be approached from either a classical or a modern perspective, but the questions are seen more acutely from the perspective of quantum theory.
William D. Hobey
Worcester Polytechnic Institute
What is curious about Barr's "Faith and Quantum Theory" is how he completely ignores every philosophy of science except scientific realism. He proceeds as if science had direct access to ontology and gives no thought to any competing philosophy, such as instrumentalism. He simply presents physicists as if they were philosophers or theologians.
So the abstractions of quantum theory somehow attain reality, a reality only physicists can ascertain. Last year, in "The Miracle of Evolution," Barr agreed that science should be "metaphysically modest" (Cardinal Schonborn's phrase), but here he presumes that physicists can determine whether determinism is real.
Scientists need to decide whether they are in the philosophy business. If they are, they should compete with all philosophies. If they are not, they should stop claiming special access to truth about reality.
Stephen Barr attempts to explain for us the Copenhagen and other interpretations of quantum mechanics. Perhaps he should have cited a blunter version of Feynman's comment on quantum mechanics, to the effect that whoever claims to understand it doesn't know what he is talking about. And how could anyone understand it when its great prophet, Werner Heisenberg, frankly stated in his Physics and Philosophy that at the quantum level the law of noncontradiction has to be abandoned. This, of course, means that his view had to be unintelligible nonsense.
Violation of the law of noncontradiction should have been a red flag to Heisenberg and Niels Bohr. Instead, Heisenberg abandoned the long-held concept of science as a description of reality and substituted an instrumental notion of science. The equations work, but they don't describe the underlying reality. The older, realist view that the equations of science represented the underlying physical realities was grievously wounded and has yet to recover.
But in 2000, with the publication of his Collective Electrodynamics: Quantum Foundations of Electromagnetism, California Institute of Technology professor Carver Mead cut the Gordian knot of wave-particle duality with his evidence that purported that such quantum particles as the electron, proton, and neutron are waves simply. In so doing, Mead restored to us a rational physics. I don't think that the philosophical and theological implications of quantum mechanics can be discussed any longer without coming to grips with Mead's work, which I reviewed for Touchstone's September 2003 issue ("Recovering Rational Science").
Barr, of course, is merely pointing out that a quantum mechanics based on wave-particle duality doesn't support philosophical determinism. My point is that any such quantum mechanics undermines both rationality and rational science. Physical determinism we can live with, but irrationality is fatal to both science and revealed religion.
"Faith and Quantum Theory" is excellent on the nature of light. Yet, as the merest amateur of the philosophy of science, may I suggest that when Professor Barr speaks of the different schools of thought in physics today, he would have been clearer if he had used the Aristotelian-Scholastic principles of act and potency. For example, the Schrodinger equations leave all possibilities in play. I interpret this to mean, philosophically, that all possibilities exist, but only in the mind of God, because God is all act and knows all possibilities as actual. This can be true only of God.
Also, it would be possible for both situations of the light collection to be real only in the mind of God; but in the physical-temporal world, only one could be actual, while the other must remain only possible.
Stephen M. Barr replies:
Robert C. Whitten confuses determinism with predictability. Physical determinism, as formulated by Laplace, asserts that an infinite mind having complete knowledge of the present state of the physical world could calculate its future development. The fact that, in practice, human beings cannot do this is beside the point. The prevalence of chaos (in the scientific sense) does make the world less predictable but does not in itself afford an escape from determinism. (In fact, chaotic behavior was first studied and is best understood in classical deterministic systems.) As for Bohmian theory, the "nonlocal" aspects of it make it no less deterministic. Peter Hodgson, a distinguished advocate of Bohmian theory, acknowledges that it is deterministic, as one can see from Peter Pagan's letter.
As noted by Pagan, the way Hodgson reconciles the putative determinism of the laws of physics with free will is by appealing to the fact that God can suspend those laws to allow humans to act freely. Since God has that power, Pagan is right to say that the reality of free will does not compel one to accept the Copenhagen interpretation of quantum theory or any other nondeterministic theory of physics. Pagan senses that I am somewhat skeptical of the idea that God suspends the laws of physics whenever human beings act freely. He therefore wonders whether I deny God's power over nature or the reality of supernatural miracles. Of course, I affirm both. My hesitation in embracing Hodgson's solution to the problem of free will comes from the fact that miracles seem to be extraordinary events and dramatic manifestations of divine power, whereas most free human acts are not. Because human free will, being a spiritual power, is beyond the laws of physics, it needn't involve a suspension of them. Yet it might, and I regard Hodgson's suggestion as perfectly reasonable. I enthusiastically second Pagan's endorsement of Hodgson's writings on science and religion, which are of unexcelled lucidity and soundness.
Adam DeMuro asks me to explain more fully why I presently prefer standard quantum theory and its traditional (Copenhagen) interpretation to Bohmian theory. The reasons are not primarily metaphysical but scientific. In my article, I claimed that Bohm's modification of quantum theory sacrificed much of its beauty. The beauty I had in mind lies in its theoretical unification of matter and forces, which are now understood to be two manifestations of "quantum fields." This is one of the greatest triumphs in the history of science. Quantum theory unites in a profound way particles with waves, and therefore with fields and forces. In fact, forces can be understood in two mathematically equivalent ways: as arising from "field lines" stretching between objects, as Faraday imagined them, or as due to the exchange of "virtual particles" between the objects, as pictured by Feynman. This wonderful synthesis emerges when quantum principles are applied in a thoroughly consistent manner to produce what is called quantum field theory. Our present, extremely successful theory of all known, nongravitational physics (called the standard model of particle physics) is a quantum field theory. Since Bohmian theory severs the wave-particle duality, it unravels the particle-wave-field-force connection. This makes it quite doubtful that a full quantum field theory can be constructed within the Bohmian framework. Certainly, that has not been accomplished to date (though a few people have been working on it recently). For this reason, I think Bohmianism will ultimately prove inadequate as a scientific theory. As far as metaphysics is concerned, Bohmian physics, being essentially Newtonian, readily lends itself to materialist monism, whereas the traditional interpretation of quantum theory seems necessarily to refer to rational mind as something distinct from inanimate matter.
William D. Hobey's point about Planck's and Einstein's roles in developing the quantum idea is correct. I did not see the need, however, to go into that level of historical and technical detail. Hobey's second point is not correct. The idea that each photon goes through just one window is emphatically not the "presently accepted" view. Indeed, the idea that particles follow many paths at once is the basis of the most modern and powerful mathematical formulation of quantum theory, called the Feynman Path Integral Formalism. Only in the "classical limit" is it a good approximation to say that particles follow a single path or trajectory. Baseballs do, but photons and electrons do not. (Ironically, it is in Bohmian theory, which Hobey says he "dismisses," that one can say that each photon goes through just one window while sensing the openness of the other window. The "sensing" happens by the "nonlocal" forces to which Whitten's letter refers. In Bohmianism, particles are like confetti in the wind. The wind pattern reflects the openness of both windows, but each piece of confetti goes through just one.) Hobey is also wrong in supposing that string theory is an "alternative" to quantum theory. String theory is based on standard postulates of quantum theory.
The "interconnectedness of all phenomena" in quantum physics referred to by Hobey is one of the main reasons that some people see an affinity with Eastern mysticism. My point was not so much to "dismiss" Buddhist ideas as to note that on a very central issue, namely the radical distinction between knower and known, the traditional interpretation of quantum theory is closer to Western than to Eastern thought.
Both Ralph Gillmann and David Haddon raise the thorny question of instrumentalism and the relation of quantum theory to reality. Many people have said that the traditional interpretation of quantum physics necessarily entails an instrumentalist view of science. That depends on what one means by instrumentalism. I believe that science, including quantum physics, makes objectively true statements about the real world and helps us to understand that world as it really is in itself. I reject views that say that modern science is merely useful or successful in manipulating (as opposed to understanding) the world, or that it merely "saves the appearances," or that it deals only with sensible phenomena rather than with the reality underlying them, or that it studies just the accidental quantitative aspects of things rather than their essences. All such views, whether they stem from nominalism, Humeanism, Kantianism, instrumentalism, or positivism, involve a gross underestimation of the explanatory successes of modern science and the power of human reason.
Gillmann is right that science has no special "direct access to ontology." What science, philosophy, and other branches of knowledge do have is the access to reality afforded by the use of reason, which may be fairly direct or extremely indirect. Gillmann is also right that the abstractions of science do not "attain reality" in the sense of becoming concrete objects, but they do refer to real aspects of the world and are necessary for correctly understanding it, at least for finite minds such as ours, which must use discursive reason.
Science is not philosophy (if we use the terms in the modern sense). A scientific theory is one thing and its philosophical interpretation or significance another. That is why quantum theory, on whose mathematical rules everyone agrees, is given wildly divergent philosophical interpretations by intelligent and informed people. It can be interpreted in ways that are materialist or nonmaterialist, deterministic or nondeterministic, realist or instrumentalist. It is the same with evolution and the Darwinian mechanism of natural selection, which can be interpreted in atheistic ways or in religious ways. Scientists become arrogant (rather than "metaphysically modest") when they pretend such divergent interpretations do not exist or claim all but one are "unscientific."
Scientists as scientists are not "in the philosophy business," as Gillmann puts it. That should not debar them, however, from holding philosophical views. Moreover, it happens that philosophizing usefully about physics requires knowing something about it; so physicists, while not in the business of philosophy, can certainly be helpful to those who are.
David Haddon notes that Heisenberg once wrote that the law of noncontradiction is violated in quantum theory. This raises the question of what is meant by the "Copenhagen interpretation." Does it include every comment ever made by Bohr or Heisenberg? If so, then it is, just as Haddon says, "unintelligible nonsense." That is why some prefer the less loaded terms "traditional interpretation" or "standard interpretation." In quantum physics, one faces a crucial question: When an observer judges an outcome to have happened, is that the only outcome that really happened, or did all the other possible outcomes also really happen in other slices of the universe (seen by the observer's alter egos)? If one says the former, one has adopted some version of the traditional interpretation. If one says the latter, one has adopted some version of the many-worlds interpretation. The traditional interpretation, so defined, can be further interpreted in a variety of directions. It can lead to solipsism, extreme instrumentalism, subjectivism, or nutty ideas about logic. I don't think it has to lead to any of those disasters, however, or I wouldn't take it seriously. I heartily agree with Haddon that irrationality is inimical to true religion, but so, I would say, is the tendency to equate the mysterious or paradoxical with the irrational. As for the Carver Mead book that Haddon refers to, it proposes some interesting speculations but only sketchily develops them. They are only the germs of ideas, and it seems to me that little will grow from them. The fact that his book has been almost completely ignored by theoretical physicists shows that I am not alone in this judgment.
Paula Haigh's suggestion that the Aristotelian concepts of act and potency may be of relevance to the issues raised by quantum physics is interesting. Others have had the same thought, including Heisenberg himself, and more recently the physicist Wolf gang Smith.
I find it strange that few of the many letters FIRST THINGS received about my article dwelt on what I took to be its most significant point, namely that a powerful antimaterialist argument can be developed from quantum physics. Even many materialist physicists would agree with the following proposition: If quantum theory as we have known it for more than eighty years is correct, and if one also takes the materialist view that human beings are merely complicated physical systems, then some version of the many-worlds interpretation is probably unavoidable. This means that materialism must now carry some very heavy baggage.…