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Buddhist-Christian Studies 22 (2002) 149-162

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Buddhist-Christian Complementarity in the Perspective of Quantum Physics

Lai Pan-chiu
Chinese University of Hong Kong


The idea of Buddhist-Christian complementarity is by no means new. 1 But what is meant by "complementarity"? In quantum physics, the concept of "complementarity" has been extensively discussed due to the principle of complementarity introduced by Niels Bohr (1885-1962). This principle is also one of the hotly debated issues in the areas of religion and natural science. Many scholars attempt to show that there are cases in Christian theology comparable to the complementarity in quantum physics. The most discussed case is perhaps the Christological doctrine of two natures in Jesus Christ. 2 Some scholars even attempt to interpret the relationship between theology and science in terms of complementarity. 3 This kind of discussion is not merely fanciful imagination originated by Christian theologians, since even Niels Bohr himself did advise Christian theologians to apply the complementary way of thinking in theology. 4 An interesting question may then be whether the principle of complementarity in quantum physics may cast light on the problem concerning Buddhist-Christian complementarity. This is the issue this essay attempts to address.

Complementarity in Quantum Physics

Modern physics, especially the theory of relativity and quantum physics, as Werner Heisenberg pointed out, brings forth to us an important philosophical issue—the relationship between language and reality. Some modern physicists find that they have to make use of ordinary language to establish a visual understanding or presentation of some events, which can hitherto only be expressed by a bundle of mathematical formulae. However, the ordinary language, together with its derived concepts, used in classical physics cannot adequately interpret some of the discoveries of modern physics. For example, conventional concepts of time and space can no longer apply directly in the general theory of relativity. The inadequacy of the classical concepts of "wave" and "particle" in quantum physics is another illustrative case. According to Bohr's theory, physicists can make use of these classical concepts in a [End Page 149] loose way, even though these concepts may seem to contradict each other when applied together. 5

The principle of complementarity proposed by Niels Bohr refers specifically to the use of the two seemingly contradictory concepts in classical physics—"particle" and "wave"—to explain the behavior of a particular entity, light. Wave and particle are mutually exclusive concepts in classical physics. According to the classical understanding, wave possesses some characteristics that particle does not have, such as reflection, refraction, diffusion and interference. In reverse, particle also possesses some characteristics that wave does not have, such as occupying certain space. However, quantum physicists have discovered that in some experiments, light "behaves" as wave, whereas in others it behaves as particle. The results of experiments seem to suggest that neither "wave" nor "particle" can adequately explain the quantum phenomena. For this reason, some physicists, including Albert Einstein, suggest abandoning the use of the concepts of wave and particle in the subatomic realm. Contrary to this view, Bohr insists that the concepts of "wave" and "particle" remain usable and useful in quantum physics because "however far the phenomena transcend the scope of classical physical explanation, the account of all evidence must be expressed in classical terms." 6 As Bohr puts it, "the fundamental postulate of the indivisibility of the quantum of action is itself, from the classical point of view, an irrational element which inevitably requires us to forego a causal mode of description and which, because of the coupling between phenomena and their observation, forces us to adopt a new mode of description designated as complementary in the sense that any given application of classical concepts precludes the simultaneous use of other classical concepts which in a different connection are equally necessary for the elucidation of the phenomena." 7

The principle of complementarity can thus be understood as a method or "mode of description" using two or more mutually exclusive concepts of a specific realm (classical physics) to explain a phenomenon of another realm (quantum physics) that...