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Quantum Physics and TheologyAn Unexpected Kinship
By JOHN POLKINGHORNE
Yale University PressCopyright © 2007 Yale University
All right reserved.
Chapter OneThe Search for Truth
PEOPLE sometimes think that it is odd, or even disingenuous, for a person to be both a physicist and a priest. It induces in them the same sort of quizzical surprise that would greet the claim to be a vegetarian butcher. Yet to someone like myself who is both a scientist and a Christian, it seems to be a natural and harmonious combination. The basic reason is simply that science and theology are both concerned with the search for truth. In consequence, they complement each other rather than contrast one another. Of course, the two disciplines focus on different dimensions of truth, but they share a common conviction that there is truth to be sought. Although in both kinds of enquiry this truth will never be grasped totally and exhaustively, it can be approximated to in an intellectually satisfying manner that deserves the adjective 'verisimilitudinous', even if it does not qualify to be described in an absolute sense as 'complete'.
Certain philosophical critiques notwithstanding, the pursuit of truthful knowledge is a widely accepted goal in the scientific community. Scientists believe that they can gain anunderstanding of the physical world that will prove to be reliable and persuasively insightful within the defined limits of a well-winnowed domain. The idea that nuclear matter is composed of quarks and gluons is unlikely to be the very last word in fundamental physics-maybe the speculations of the string theorists will prove to be correct, and the quarks, currently treated as basic constituents, will themselves turn out eventually to be manifestations of the properties of very much smaller loops vibrating in an extended multidimensional spacetime-but quark theory is surely a reliable picture of the behaviour of matter encountered on a certain scale of detailed structure, and it provides us with a verisimilitudinous account at that level.
Theologians entertain similar aspirations. While the infinite reality of God will always elude being totally confined within the finite limits of human reason, the theologians believe that the divine nature has been revealed to us in manners accessible to human understanding, so that these self-manifestations of deity provide a reliable guide to the Creator's relationship with creatures and to God's intentions for ultimate human fulfilment. For the Christian, this divine self-revelation centres on the history of Israel and the life, death and resurrection of Jesus Christ, foundational events that are the basis for continuing reflection and exploration within the Church, an activity that the community of the faithful believes to be undertaken under the guidance of the Holy Spirit. Revelation is not a matter of unchallengeable propositions mysteriously conveyed for the unquestioning acceptance of believers, but it is the record of unique and uniquely significant events of divine disclosure that form an indispensable part of the rational motivation for religious belief.
Both these sets of claims for truth-bearing enquiry are made in conscious conflict with much of the intellectual temper of our time. In many parts of the academy the movement broadly called postmodernism holds sway. It emphasises what it sees as the uncertain basis of human knowledge, a vulnerability to challenge that results from the inescapable particularity of perspective imposed by the need to interpret experience before it can become intelligible and interesting. The necessary cultural context of language is held to imply that there is no universal discourse, but only a babble of local dialects. The grand modernist programme of the Enlightenment, alleged to be based on access to clear and certain ideas that are unquestionably acknowledged to be universally valid, is asserted to have been no more than the imposition of the perspective of white male Western thinkers, treated as if such attitudes were a non-negotiable rule for all. According to postmodernism, casting off these modernist shackles liberates twenty-first-century thinkers into being able to accept a creative plurality of ideas, thereby enabling participation in a conversation in which nobody's opinion has a preferred priority.
We certainly need to acknowledge that rational discourse is a more subtle matter than Enlightenment thinkers were able to recognise. Yet in the eyes of its practitioners, science does not at all look like a free market in ideas of an eclectic kind. We shall attempt to specify its character in more detail shortly, but one must begin by considering how it actually progresses. The more extreme postmodernists would challenge the use of that last verb, but can one really suppose that the concepts of the helical structure of DNA and the quark structure of matter do not represent clear advances in understanding, intellectual gains that have become a persisting part of our understanding of the world? These ideas evolved under the irresistible nudge of nature, and not as fanciful notions whimsically adopted by the invisible colleges of molecular biologists and particle physicists respectively. Once the famous X-ray photographs taken by Rosalind Franklin had been seen and understood, there could be no doubt that DNA was a double helix. Once the data on hadronic structure (the patterns found in the properties of particles that make up nuclear matter), and the results of deep inelastic scattering (a particularly penetrating experimental probe), had been collected and assessed, there could be no doubt that fractionally charged constituents lay within protons and neutrons. Of course, interpretation was necessary-raw data such as marks on photographic plates are too dumb to speak of structure directly-but the naturalness of the interpretation, and its confirmation through a continuing ability to yield more understanding in the course of further lengthy investigations, is sufficient to convince scientists of the verisimilitudinous character of their theories. It is difficult for those not involved in scientific research to appreciate how difficult it is to discover theories that yield persistently fruitful and elegantly economic understanding of extensive swathes of experimental data, and therefore how persuasive such understandings are when they are attained. For those of us who were privileged to be members of the particle physics community during its twenty-five-year struggle to understand nuclear matter-an activity that eventually led to the Standard Model of quark theory-the enterprise had precisely this convincing character. The experimentally driven investigation, often proceeding in directions quite different from the prior expectations of the theorists, was no indulgence in the construction of pleasing patterns, but it was the hard-won recognition of an order in nature that is actually there.
A just account of science lies, in fact, somewhere between the two extremes of a modernist belief in a direct and unproblematic access to clear and certain physical ideas, and a postmodernist indulgence in the notion of an à la carte physics. The intertwining of theory and experiment, inextricably linked by the need to interpret experimental data, does indeed imply that there is an unavoidable degree of circularity involved in scientific reasoning. This means that the nature of science is something more subtle and rationally delicate than simply ineluctable deduction from unquestionable fact. A degree of intellectual daring is required, which means that ultimately the aspiration to write about the logic of scientific discovery proves to be a misplaced ambition. Yet the historical fact of the cumulative advance of scientific understanding implies that the circularity involved is benign and not vicious. In assessing the character of science and its achievements, we need to be sufficiently tinged with postmodernism to be able to recognise that there is a measure of rational precariousness involved in its interweaving of theory and experiment, but also sufficiently tinged with a modernist expectation of intellectual attainment to be able to do justice to science's actual success. The philosophical position that mediates between modernism and postmodernism is commonly called critical realism, the adjective acknowledging the need to recognise that something is involved that is more subtle than encounter with unproblematic objectivity, while the noun signifies the nature of the understanding that it actually proves possible to attain.
I believe that the philosopher of science who has most helpfully struck this balance has been Michael Polanyi. He knew science from the inside, since he was a distinguished physical chemist before he turned to philosophy. In the preface to his seminal book Personal Knowledge, Polanyi wrote,
Comprehension is neither an arbitrary act nor a passive experience, but a responsible act claiming universal validity. Such knowing is indeed objective in the sense of establishing contact with a hidden reality ... Personal knowledge is an intellectual commitment, and as such inherently hazardous. Only affirmations that could be false can be said to convey objective knowledge of this kind ... Throughout the book I have tried to make this situation apparent. I have shown that into every act of knowing there enters a passionate contribution of the person knowing what is known, and this coefficient is no imperfection but a vital component in his knowledge.
These convictions are worked out in great detail in the book, drawing on Polanyi's scientific experience in a way that other scientists can readily recognise as being authentic. He stresses not only commitment but also the tacit skills involved (for example, in evaluating the adequacy of theories and in assessing the validity of experiments in actually measuring what they are claimed to measure and not some spurious side-effects) that call for acts of judgement that cannot be reduced to following the rules of a specifiable protocol. The method of science has to be learnt through apprenticeship to the practice of a truth-seeking community, rather than by reading a manual of technique, for, in a phrase that Polanyi often repeated, 'we know more than we can tell'. This role for skilful judgement gives scientific research a degree of kinship with other human skilful activities, such as riding a bicycle or judging wine, that require the exercise of similarly tacit abilities. Though the subject of science is an impersonal view of the physical world, its pursuit is an activity of persons that could never be delegated simply to the working of a well-programmed computer. These personal acts of discovery are then offered for assessment and sifting within a competent community, whose judgements are made with the universal intent of gaining reliable knowledge of the physical world. The actual character of our encounter with that world remains the controlling factor. These last points save the personal knowledge of science from fragmenting into a loose collection of individual opinions.
I want to add a further note of a theological kind to the discussion, with the intent of making more intelligible this remarkable ability of scientists to gain such reliable knowledge of the universe, despite the degree of unavoidable epistemic precariousness involved in the endeavour. It is a fact of experience that this repeatedly proves possible, even for phenomena occurring in regimes that are remote from direct human encounter and whose understanding calls for ways of thought quite different from those of everyday life (quantum theory; cosmology)-a fact, incidentally, that undermines the invocation of Darwinian evolutionary process as an all-sufficient explanation. The widespread success of science is too significant an issue to be treated as if it were a happy accident that we are free to enjoy without enquiring more deeply into why this is the case. Critical realist achievements of this kind cannot be a matter of logical generality, something that one would expect to be attainable in all possible worlds. Rather, they are an experientially confirmed aspect of the particularity of the world in which we live and of the kind of beings that we are. Achieving scientific success is a specific ability possessed by humankind, exercised in the kind of universe that we inhabit. I believe that a full understanding of this remarkable human capacity for scientific discovery ultimately requires the insight that our power in this respect is the gift of the universe's Creator who, in that ancient and powerful phrase, has made humanity in the image of God (Genesis 1:26-27). Through the exercise of this gift, those working in fundamental physics are able to discern a world of deep and beautiful order-a universe shot through with signs of mind. I believe that it is indeed the Mind of that world's Creator that is perceived in this way. Science is possible because the universe is a divine creation.
In its turn, theology is not unacquainted with the necessity of circularity. Augustine and Anselm both emphasised the pattern of 'believing in order to understand' as well as 'understanding in order to believe'. No quest for truth can escape from the necessity of this hermeneutic circle, linking the encounter with reality to an interpretative point of view, so that they are joined in a relationship of mutual illumination and correction. Religious insight is not derived from the unhesitating acceptance of fideistic assertion (as if belief were simply imposed by some unchallengeable external authority, conveying to us indubitable propositions), but neither can it be based simply on argument controlled by the conventions of secular thought (such as, for example, the assumption of a purely naturalistic historicism that what usually happens is what always happens). Theology, as much as science, must appeal to motivated belief arising from interpreted experience. Of course, in the case of theology the kind of experience, and the kinds of motivated beliefs that arise from its interpretation, are very different from those appropriate to the natural sciences. The latter enjoy possession of the secret weapon of experiment, the ability to put matters to the test, if necessary through repeated investigation of essentially the same set of impersonal circumstances. This enables science thoroughly to investigate a physical regime defined by a definite scale (such as a given energy range) and to make an accurate map of it. From this ability arises much of the cumulative character of scientific understanding, a linear process in which knowledge increases monotonically. Even in sciences such as palaeontology, where scale is not a controlling factor and significant past events are not repeatable, evidence accumulates in forms that remain permanently accessible, to which direct recourse can be made for further assessment if required.
By way of contrast, in all forms of subjective experience -whether aesthetic enjoyment, acts of moral decision, loving human relationships, or the transpersonal encounter with the sacred reality of God-events are unique and unrepeatable, and their valid interpretation depends ultimately upon a trusting acceptance rather than a testing analysis. The pattern of understanding that results is, so to speak, multidimensional rather than linear, with no necessary implication of a simple temporally ordered increase, as if the insights of the present were inevitably superior in all respects to the insights of the past. Four distinctive features of religious experience express the contrast between science and theology in these respects.
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