The Physicist as Philosopher

One of the minor crosses that Albert Einstein bore through the last thirty years of his life was the way in which people of all kinds and backgrounds turned to him for pronouncements: pronouncements about democracy and liberty, about aesthetics and free love—above all, about philosophy. Just because of the intellectual penetration shown in his analysis of our spatial and temporal concepts, they hoped for a further revelation; and indeed, the term “relativity” became for a while a catch-phrase far beyond the widest-drawn boundaries of mathematical physics. On his own side, Einstein himself was fully aware of the limitations of his experience, and felt keenly embarrassed when his personal opinions were treated with inappropriate deference. Some people may be tempted to comment, “And quite right, too!” Yet there is a little more to the matter than this. Throughout intellectual history there has been a continuous interaction at the theoretical level between the ideas of physics and those of philosophy—between physics (one might say) and the rest of philosophy, since today’s physical theory is the lineal descendant of yesterday’s “natural philosophy.” Certain genuinely philosophical problems—e.g., those at issue between Leibniz and Clarke—lose most of their force and point for twentieth-century readers if divorced from scientific considerations; and over such issues the contributions of a Poincaré or an Einstein may in fact help directly to clear our philosophical minds. The patterns of interaction between physics and philosophy are, however, not fixed timelessly: they change from generation to generation. The specific relevance of new modes of thought in physical theory to (say) epistemology or philosophical theology is something which has continually to be explored afresh. So the philosophical views of physicists of such intellectual distinction as Niels Bohr or Erwin Schrödinger must be of interest both for biographical reasons and more generally.

Since the time of Tycho Brahe, Denmark has surely had no more profound scientific thinker than Niels Bohr. By the time of his death, he was probably the most widely respected, and certainly the most widely loved man in his profession. Like his teacher Ernest Rutherford, he was a natural leader: his home at Copenhagen was the center of a series of concentric intellectual circles, which expanded outwards to embrace the whole world-community of theoretical physicists. In a century of growing scientific nationalism, too, he was the last of the instinctive scientific internationalists: his abortive wartime interview with Churchill (described in Mrs. Gowing’s recent history of the British atomic energy program) had an irony worthy of Berthold Brecht. Scientifically, Bohr made an enduring mark as the Pythagoras of atomic structure—as the man who saw how, from the sharply-defined wavelengths in the line-spectra of electrically-excited gases, one might decipher the internal arrangement of the electrons in the gas-atoms. (This was the discovery which led Einstein to exclaim, echoing Kepler, “Hier ist höchste Musikalität im Raüme des Gedenkens.”)

Philosophically, Bohr’s mind became occupied more and more with the idea of “complementarity,” which he endeavored to expand from its starting-point in physics to resolve intellectual quandaries on a wider scale. The nub of the idea is this. If we study the behavior of light, scrutinizing especially the ways it interacts with material substances, we shall find the results we obtain falling into two contrasted groups. On the one hand, there are effects which display analogies to those already familiar to us from our experience of waves: refraction, diffraction, and so on. On the other, there are properties (e.g., the “photo-electric effect”) which compel interpretation in terms of atomistic analogies: the energy of light apparently travels in minimum bullets or packets—the so-called “photons.” Mathematically, we can build up a single set of concepts and equations capable of matching both groups of effects: intuitively, we can grasp the mechanism of the effects only by employing alternative, “complementary” analogies, and by conceding from the outset that this duality or “complementarity” lies at the base of our theory.

Within physical theory the idea of complementarity had, and has, a clear and specific meaning. Two older images, each of which seemed to nineteenth-century physicists to apply with absolute precision in its own sphere, turn out on a finer level of analysis to be only complementary analogies, reflecting partial aspects of a single, more sophisticated type of process. The definitive description of the realities in question cannot be fully expressed in terms of either picture singly: it demands its own more complex terms. Yet the very fact that two conceptions apparently so antagonistic to one another could be reconciled in a more comprehensive theory filled Bohr with a larger hope. Perhaps other—even all—philosophical antitheses could be resolved in the same way. Perhaps in these other cases, too, the fundamental error consisted in demanding a single unique answer, a single unique image, where the complex reality in question called for a richer type of characterization:

In general philosophical perspective, it is significant that, as regards analysis and synthesis in other fields of knowledge, we are confronted with situations reminding us of the situation in quantum physics. Thus, the integrity of living organisms and the characteristics of conscious individuals and human cultures present features of wholeness, the account of which implies a typical complementary mode of description.

Mechanism and vitalism in biology, objective behavior and subjective feelings in psychology, East and West in politics: the secret of understanding in each case lay in taking a sufficiently comprehensive view, and reinterpreting rival doctrines as complementary ones.

The outcome of this approach was only partly satisfactory. For it led Bohr to adopt a “chairman’s philosophy,” which sketched the forms of possible reconciliations rather than the concrete details of actual settlements. Invited to address an International Congress of Pharmaceutical Sciences, or the opening of an Institute of Genetics, he was too friendly to refuse; but the resulting speech tended to be more eirenetic and oecumenical than constructive. For, in philosophy, the injunction to “reconcile antitheses” does not get one very far. Philosophical perplexity begins seriously only when the arguments leading to two antithetical conclusions make them, on the face of it, equally inescapable yet mutually inconsistent. Perhaps, in an intellectual heaven, the Aristotelian lion will lie down with the Platonist lamb: in the meanwhile, the problem of finding a statement which will satisfy them both calls for something more precise and specific than the idea of complementarity.

In Bohr’s own published addresses, this detailed and concrete spelling-out of the notion of complementarity in fields other than his own professional field of atomic physics is continually hinted at, but nowhere actually forthcoming. This is true of much of the latest slim collection of essays and speeches, dating from the final year of his life, as it was of its predecessors. There are suggestions in places (such as in the passage quoted above) that he would have supported some kind of “holist” doctrine, and indeed there is a flavor of Goethe in many of his philosophical attitudes. At crucial points, however, the idea of complementarity dissolves into an analogy:

Words like thoughts and sentiments refer to mutually exclusive experiences and have therefore since the origin of human language been used in a typically complementary manner. Of course, in objective physical description no reference is made to the observing subject, while in speaking of conscious experience we say “I think” or “I feel.” The analogy to the demand of taking all essential features of the experimental arrangement into account in quantum physics is, however, reflected by the different verbs we attach to the pronoun.

As a historical record, by contrast, these essays have a real value. They include the Rutherford Memorial Lecture (1958) as well as two other, briefer discussions of the historical development of quantum theory, which between them preserve for us many of Bohr’s first-hand recollections of the physicists of the first “sub-atomic” generation. Philosophically speaking, one should not examine the arguments of these essays too closely, but one accepts the collection nonetheless—like garden roses in December—with affection and gratitude for a rich intellectual harvest.

If, in his excursions beyond the intellectual boundaries of physics, Niels Bohr was (to put it unkindly) something of an Eisenhower, Erwin Schrödinger was by comparison a T. E. Lawrence—a deeply reflective, idiosyncratic man, with the urge to embark on solitary long-range penetrations into the intellectual desert. Schrödinger never gathered a great circle of physicists around him, as Bohr did; yet for some of us the originality of his contributions to contemporary physical thought is unequalled. For it was he who took Louis de Broglie’s speculation that matter (as much as light) might have a wave-aspect as well as a particle-aspect, and made it the basis of a complete mathematical analysis of atomic structure. The stable states of the atom, which Bohr had recognized in his theory of spectra, Schrödinger explained as so many “harmonics” in a system of matter-waves. If electrons were “wave-bundles” rather than “point-masses,” then the excitation of an atom by a photon need not (as in Bohr’s theory) involve the sudden removal of an individual point-electron from one planetary orbit to another. Rather, it might be like a switch in the wave-pattern within a resonant chamber (a flute, say) from one tone to its octave or twelfth. Nor was this just a façon de parler; it could be worked out as a consistent—and successful—mathematical theory. The resulting system of “wave-mechanics” was as much a break with the atomistic ideas which had been the dominant tradition in physics ever since Newton as the ideas of the Stoic philosophers (to which Sambursky has compared Schrödinger’s theory) were a break with the atomism of Democritus and Epicurus.

Despite the depth of his theoretical insights, however, Schrödinger never made any serious attempt to generalize them, or to use them as foundations for a philosophical structure. When he turned from physics or bio-physics (on which he threw some valuable sidelights) to wider branches of philosophy, he set aside all scientific analogies, and faced the new range of experiences directly. So the two essays in his little book My View of the World, originally written thirty-five years apart and now published for the first time in English translation, make no attempt to extend into a wider sphere the physical ideas with which his name has been associated. Instead, they present a case which many readers will find surprising: following a lead from the Indian Vedanta, Schrödinger argues for what he calls “the doctrine of identity”—the doctrine that all our individual selves are linked in a single all-embracing reality. Though, at a certain level, what solipsism means is un- deniable (“the absolute hermetic separation of my sphere of consciousness from all others”), there are features of our experience which point beyond this fragmentation of the world into separate individuals. The “far-reaching structural similarity in our experiences” reflected in our development of a common language, and the “extensive agreement or paralielisms in what is called the external part of our spheres of perception,” give him hope that we may break out of the prison-house of our “selves,” since they appear fully intelligible to him only if all our personal experiences are regarded as so many aspects of a single shared reality—this reality itself being neither specifically “material” nor specifically “mental.”

From outside, we can appreciate how natural this deliberate rejection of materialism in general philosophy must have seemed to a man who, in physics also, was helping to blur the hard conceptual boundaries of nineteenth-century matter-theory, and reinterpreting the properties of material objects (even for the purposes of physical science) in terms of a wave-theory of matter. Yet Schrödinger himself carefully avoided claiming any scientific warrant for his point of view. He rested his Weltanshauung solely on philosophical and experiential arguments, and he presented these arguments with a genuine and appealing modesty. All that could be proved, he declared, was that the dualism of mind and matter was a metaphysical dogma and not (as was often supposed) a self-evident fact. The further, Vedantic conclusion “that we living beings are all simply sides or aspects of one single Being” was unprovable; but it was something in which Schrödinger personally found intellectual support for a Schweitzer-like ethics of “reverence for life.”

In so condensed a statement—the two essays together run out at less than thirty thousand words—it is not easy to disentangle the strictly philosophical arguments from the purely personal affirmations. Leaving aside Schrödinger’s reliance on the community of language (which proves only that all attempts to communicate have not been wholly unsuccessful), his epistemological arguments led him to few positive conclusions: all he was anxious to do was to clear out of the way “the ‘traditional’ legend that in our sensibly perceived environment…we can easily and conveniently distinguish between two kinds of qualities, primary and secondary.” It was this “bizarre legend” that enshrined (as he saw it) the obnoxious dichotomy between material bodies, on the one hand, and the individual minds locked within them, on the other.

The step onwards from this, essentially negative, philosophical position—and there can be few philosophers today who would regard the old empiricist distinctions as “easy” or “convenient” to draw—to Schrödinger’s Vedantic world-view is a long one; and it is a step based less on arguments than on sympathies. Still, Schrödinger himself does not pretend to be giving us any more than a provisional aperçu, in a region of experience where scientific enquiry has up to now scarcely gained a foothold. And, at a time when in the Western world Vedanta and Zen have been made a fad by the most inexact of non-scientists, it is good to have an Oriental viewpoint restated, with style and restraint, by a mathematical physicist who was also a profound humanist.

Both Schrödinger and Bohr here leave the bearing of contemporary physics on general philosophy unexplained: Bohr because the analogies he draws between them are too tenuous to be helpful, Schrödinger because he declines to draw any such analogies. (“I do not think,” he says in his preface, “that acausality, wave mechanics, Indeterminacy relations, complementarity, an expanding universe, continuous creation etc. have as much connection as is currently supposed with a philosophical view of the world.”) It is left to Professor von Weizsäcker to examine The Relevance of Science explicitly, in the first of his two series of Gifford Lectures, originally delivered at Glasgow University in the academic year 1959-60. Weizsäcker would not pretend to be a scientist of the originality or penetration of a Schrödinger or a Bohr—such men do not come in large numbers—but his competence as a physicist is past question, and his wider understanding of the Western tradition of humanities is impressive. He differs from Bohr and Schrödinger also in one further respect: he is a professing and articulate Christian—a man who (in his own words) has “been hit by the word of Christ.” In his two series of Gifford Lectures, he attacks the intellectual problems which inevitably arise for a scientist who also is devout, first from a historical point of view, then from that of a philosopher.

To a religious agnostic like myself, the manner in which he faces this task is refreshing. After the flabby rhetoric of much recent apologetics—e.g., the writings of Teilhard—this crisp, clear and readable book is a pleasure. Throughout the modern scientific period, Christian theologians (particularly in the Protestant world) have been tempted to resist the encroachments of science by trying to dull its cutting-edge. They have done so in two ways: by fencing off a special area of spiritual matters which are to be kept immune from scientific investigation, or else by reinterpreting all the new discoveries of science, as they are made, in an edifying sense. Weizsäcker will have nothing to do with either of these devices. In his opinion, the different varieties of natural theology have been so many intellectual Vietnams—rearguard actions entered into out of desperation, whose only real justification would be to cover a disengaging movement. By now, however, it should be clear that the complete secularization of our world-picture is something both inescapable and to be welcomed. There is no need for the Christian to resist this secularization: on the contrary, any last attempts to blunt the intellectual impact of science will only distract attention from the true message of Jesus—which is not a theoretical system of cosmology, but a practical way of life having radical political implications. And the last thing we can afford in the mid-twentieth century (Weizsäcker insists) is to lose sight of that social message. The forces of conservatism and inhumanity are already too strong, without that.

There are times, as the gale that Weizsäcker looses on natural theology reaches hurricane force, when one wonders what will be left of traditional Christian doctrine after it has passed. Very little, I suspect; though probably Weizsäcker himself would not really mind. For, like Tillich and Bonnhofer and the “demythologizing” school of theologians generally, he is interested in a Christianity which will be basically non-theological and non-doctrinal. What matters most is a “correct diagnosis” of “the crisis of the life of our epoch”; and our “therapeutic exertions” must not become too dependent on “dogmatically maintained theories.” The habit of identifying one’s own standpoint with “absolute truth” he dismisses as a “historical naivety”: rather, we must come to view both the ideas of science and the moral prescriptions of Christianity in their own distinct historical perspectives.

What distinguishes Christianity, so interpreted, from a non-theistic humanism is very hard to say. Perhaps, to Weizsäcker, even the attempt to say this would be a needless concession to out-dated forms of theology. The Christian has a standpoint from which he views the development of man’s intellectual and moral life in his own way; and how the resulting spectacle differs from a humanist view (he would reply) is more easily seen than stated. This conclusion is too elusive to be wholly satisfying: attempting to grasp it, I feel like the man who, after a period of fervent atheism, read philosophy at Oxford and found that he no longer understood that which he had formerly disbelieved. Weizsäcker certainly presents the historical evolution of scientific ideas in a historical proportion which is illuminating, quite apart from all theological issues. But is there, then, nothing in Christianity for us to doubt?