MODERN PHYSICS AND THOMIST PHILOSOPHY
ONE OF THE more disquieting elements in current thought is the widespread belief outside philosophical circles in the natural sciences as the sole reliable source of knowledge, coupled with the fact that the overwhelming bulk of accessible publications on the status and interpretation of natural science is written from a positivist, materialist, or solipsistic point of view.1
These writings seem especially persuasive in connexion with modern physics, with which this article will be concerned.2 Indeed, at first sight there is a remarkable divergence between Thomist views about material nature and the model of it which the physicist builds to reproduce his observations; and a physicist superficially acquainted with Thomist philosophy is not likely to respect the latter when he compares its leading ideas with those of his own science. He cannot find, for instance, in the formulae of mathematical physics, any evidence for the analogical view of being, or the distinction of essence and existence; for his different kinds of atom differ, not in their degree of actual perfection, but merely in dimensions and complexity, and different atoms of the same kind are regarded as identical, and not as diverse manifestations of their common nature. There is no hierarchy of being discernible among the entities of physics; being, as known to physics is univocal, flat, levelled out. Again, the physicist cannot assign any immediate final cause to a physical entity; nor has he room for efficient causality, for in physics neither partner in a change is looked upon as more
1 Examples are: H. Levy, The Universe of Science; Hogben, Science for the Citizen; Dingle, Through Physics to Philosophy.
2 The field of study of modem physics may be defined as "non-living material nature," to exclude from it both living material substances and artificial entities such as chairs and statues. In what follows this defining phrase is shortened to "dead matter."
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in act than the other. (Unfortunately the word "causality" is often retained and given a special meaning.) He does not talk about substance and accident, but a great deal about functional relations; 3 he finds that when he attempts to locate a substance, physical entities have a disconcerting way of proving inadequate. "Space as known to physics is a system of coordinates; "time" is no longer the measure of motion, as in the Aristotelean definition, but is itself measured. A glance at a Thomist manual is not likely to be reassuring; it will probably state (very briefly) that physics has to do with a degree of abstraction in which one abstracts from the individual peculiarities of material things, but this is not a good description of modern mathematical physics (and of course was not intended to be). Further, natural science and Thomist manuals have become so insulated that the latter are liable to frame their natural philosophy in terms which suggest a hopeless incompetence about physics and a belief in the adequacy of notions now abandoned by physicists. The concepts of Thomist philosophy and of physics are so distinct as to be difficult of comprehension to those familiar with only one of these disciplines, and yet the vocabularies are similar enough to cause confusion. Finally, the physicist finds that his science is treated with much more deference among some philosophies outside the schools of philosophia perennis, who offer less resistance to his tendency to argue that only physics can give any solid knowledge about anything.
We have, therefore, the makings of a considerable scandal; for at present anyone who takes an interest in the more accessible literature on the philosophy of science is liable to acquire a contempt for Thomist philosophy, as well as false notions about the scope of natural science. There is a great need here for sound exposition of Thomist philosophy and its relation to the natural sciences. Happily, the latter are now much better established on the Thomist map than they were a few years ago.
M. Maritain in The Degrees of Knowledge has strenuously
3 Cf. Cassirer, Substance and Function.
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worked out the position of physics in a Thomist hierarchy of sciences; Dr. W. R. Thompson in his Science and Common Sense has dealt magisterially with biological sciences; and recently Prof. E. Rideau has written a Philosophie de la physique moderne, which includes a compact account of the actual method and structure of modern physics and the consequences of its restriction to the metrical investigation of dead matter. And on the part of philosophy itself, there is less excuse now for taking slick manuals as representative of Thomist philosophy; it has been made clear, both by Maritain’s great work and in an important study by Prof. M. Adler,4 that the question of our knowledge of the essences of material nature is complex and by no means settled in detail. Thus a great deal of ground has been cleared; but there is still much to do in bringing Thomist philosophy into contact with physics and physicists.
In the present article an attempt is made in the first section to outline the position of physics with respect to Thomist philosophy and the general reasons for their apparent divergence; this can be done after considering simply some general characteristics of physical investigation and interpretation of experimental data. In the second section, certain Thomist doctrines and the divergence of physical science from them are considered more fully. The third section outlines certain leading elements in the actual scheme of physics as at present understood, and traces their relation to the views put forward as to the scope and method of physics.
I
In the pursuit of physical and physico-chemical work there may be distinguished two processes, which depend upon and supplement each other. One is the formulation of empirical generalisations on the basis of metrical observation. The other is the construction of a mathematical interpretatory system, such that by deduction from it one can obtain numbers which
4 In The Thomist, No. 1, p. 80, and following issues.
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agree with the experimental measurements as closely as possible. In practice these processes are closely interwoven, but it is permissible to consider an idealised case in order to show that both strands are to be found in the actual structure of physics. Suppose we are investigating the relation between the pressure and the volume of a specimen of air. Both pressure and volume are defined in terms of certain measurable lengths; the experimental investigation could be performed by enclosing the air in a glass tube closed by a column of mercury, altering the length of the latter, and observing the alteration in the position of its surface as the air is compressed. A series of numerical values for one variable, pressure (x), could then be obtained, with the corresponding value for the other variable, volume (y). (Experimental inaccuracies will always prevent the figures from representing exactly the true values of the variables). All other variables, such as temperature, should be kept as constant as possible. Each pair of values of the two variables is found to be related by approximately the same simple relation, namely "x varies inversely as y "; this is shown either by plotting a graph and finding a simple curve which passes near all the points, or by finding a simple equation which is approximately satisfied by all the pairs of values. The experimental data are, then, summarised in the empirical generalisation represented by the equation: xy constant, which is a functional relation, from which the value of x may be deduced when that of y is known. An important point about this empirical generalisation is that it is a construction; none of the observed pairs of values need fit it exactly, yet it is regarded as a legitimate generalisation, with a certain likelihood of being true.5 This is less cavalier than it perhaps appears, because the observed values are themselves liable to be inaccurate. None the less, the fact that we accept such generalisations based on a limited number of inaccurate instances, constitutes a radical divergence from the positivist view, and must later be justified. For the present we accept the position that a correlation of
5 Cf. Ryle, Proc. Arist. Soc., Vol. XVI (1937), on "inductive reliability."
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two variables, each connected with experimentally-observed distances, has been followed by the formulation of an empirical generalisation, in the form of a functional relation. This is the simplest form of the inductive method used in physics.
A vast collection of these functional relations, all founded upon metrical observation, constitutes the raw material for the other process at work in physics: the construction of an interpretatory scheme. By the aid of complicated processes of comparison, analysis, imagination, trial and error, and so on, there are constructed, in thought, models of the experimentally-observed systems, tentative formulations of more fundamental properties, mathematically expressed; and a scheme is evolved such that by mathematical deduction the numerical results obtained by experiment are reproduced as accurately as possible. This scheme includes both quasi-substantive entities (such as ultimate particles, atoms, molecules), and laws (such as that of gravitation) , all mathematically defined. The variables which occur in the mathematical expressions include, besides distance which is directly measurable, some derived variables, such as energy and charge, which determine the values of certain distances and are indirectly measurable.
In summary, we may say that the nature and scope of physics depend upon its use of metrical observation, gencralisation by functional relations, and interpretation by means of constructions mathematically defined. The consequences for the actual structure of physics will be dealt with later. For the present we wish simply to use the fact that both observation and interpretation in physics are alike concerned solely with the measurable aspects of dead matter, in order to relate physics to a Thomist framework.
It is convenient, however, to mention first the view that "inductive method does not need any philosophical basis; it works." The answer to this is that it is possible to use induction without paying attention to its philosophical presuppositions6
6 If I have understood him correctly, one of Whitehead’s major contributions to the philosophy of science has been to show that the physicist as such need not wait
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since these accord with common sense; yet the validity of the presuppositions must be dealt with philosophically. In particular, induction cannot proceed without a conviction based upon philosophy that there is order in the world investigated by physics; and that our minds can come to understand it in some manner if given long enough. Recently the conditions have been worked out for a justification of inductive generalisation (confirmative induction), by means of formal logic working on the empirical data alone, and apart from the metaphysics;7 but the conclusion is that a necessary condition for such a justification would be some proof, based on formal logic alone, or on some empirical facts, that no subject can have an infinite number of attributes; and such proof is manifestly impossible. In fact, confirmative induction derives its legitimacy from a philosophical view, not based upon physical investigation, that there is order in dead matter.8 It is false then, to suppose that induction is self-validating.
We must now pass to the Thomist philosophical setting. Thomist philosophy appears very strange to those who, possibly by attention to physical science, have become interested primarily in dead matter rather than living beings. This is partly because, by contrast, this philosophy pays greatest attention to intellectual beings and the matters most vitally important to them; non-rational living organisms occupy a subordinate position, and dead matter is considered as interesting largely because it is capable of being actualised by some higher form. More specifically, Thomist philosophy places God at its apex, and is permeated with His action; it deals with God’s creation and conservation of the world; it treats of man as an intellectual being, source of his own acts, tending towards objects of knowledge and love, developing towards God; it treats of other living organisms as analogous to man in respect of life, but distinct in respect of the incomparable gift of intellect by which
for a complete solution of such problems; and to show how physics can work in a self-contained sphere, within which it is independent of philosophy.
7 Cf. J. M. Keynes, Treatise on Probability; Eaton, General Logic, Part IV.
8 It is hoped to develop this thesis more fully later.
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man is made capable of elevation to the divine plane (capax Dei). Because of this attention to living and intelligent beings, it perceives the scale of perfection among essences, the analogy of being in what might be called its "vertical" dimension; which is overlooked by those who restrict the object of their philosophising to the dead world, under the mistaken belief that where physics has been most successful there will be the best field for philosophy. Further, not being restricted to the measurable, Thomist philosophy points out the "horizontal" analogy of being, which must hold among dead substances as elsewhere, since it is necessary if substances with the same essence are to be distinct.
This analogical view of being or actual perfection,9 leads to the conclusion that a substance may fulfill the possibilities of its essence to a greater or less degree, and also that the essence itself may fulfil the possibilities of being to a greater or less degree; whence arises the distinction of potency and act. When applied to the process of change, this distinction is the basis of the distinction of four causes in every change; for, given that a substance may be more or less in act, a change consists in a being which is in act in some respect acting on another which is in potence in that respect. Consequently, the change is determined by the efficient cause, i. e. the being originally in act; the matter and form of the other being; and the final cause or term of the change. It is easy to identify these causes in the case of artifacts (though care is necessary not to forget that artifacts are only quasi-substantial~ and not to confuse this accidental change with substantial change). Consider, for example, the making of a statue in wood. The material cause is the unshaped wood; the formal cause is the form which shapes the final product. The efficient cause is multiple: the primary efficient cause is God, who gives being to both sculptor and material; the secondary is the sculptor, whose vitality is responsible for the work; the instrumental efficient cause is his chisel. The final cause also is multiple: it divides into ends of the work
9 On the equivalence of esse and actual perfection, see Fr. Hilary Carpeflter The THOMIST, Vol. I, No. 1, p. 55.
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(fines operationis) and ends of the worker (fines operantis), in each of which there is a hierarchy: thus the immediate finis operationis is the form which shapes the matter, while the ultimate end of all things is to glorify God: the immediate finis operantis is perhaps to earn a living, a further end is to fulfil a human nature, and the ultimate end is to glorify God. And, since potency and act apply to all created beings, in all changes there must be four such elements in the causation (though usually they are much harder to identify).
All these and related Thomist views depend upon the analogical view of being, which is maintained by a refusal to withdraw attention from living substances, or to deal with dead substances only from their measurable aspect.
Thomist philosophy is a synthesis, a balanced account of our certitudes (insofar as they are independent of Revelation); and dead matter, however tractable to physics, is not regarded as the type of being. This constitutes a difference from certain post-Renaissance philosophies which have dropped the attempt to form a commentary covering all the objects of experience, and have concentrated on that minimal aspect which is dealt with by physics. It would be impossible to treat this theme adequately in a short space, and an unsympathetic treatment would be worse than useless; but with suitable reservations, it may be said that Descartes’ system, formulated as a mere prologomenon to his physics, explicitly neglects final causes and attempts to reduce all being to the type dealt with in mathematics; and that Kant in the Analytic attempts to find an apodictic proof, not based upon ontology, that there must be physical laws, while in the Dialectic he condemns metaphysics. In consequence, such modern philosophy as derives from these thinkers is liable to be unduly preoccupied with physics, to its own stultification (because the philosophical basis of induction is neglected), and to the neglect of what is enormously more important. It is also incapable of providing the proper setting for natural science.
We can now deal more specifically with physical science. Physics (in its modern, not its Aristotelean sense; cf. p. 217),
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is concerned with non-living material nature, which we agreed (note 1) to refer to as "dead matter." Dead matter is near the bottom of the Thomist scale, the first stages above the unknowable prime matter; it can be given accidental forms by man for use or for the sake of beauty, and it can be informed with life and with a rational soul by God. It is therefore in potency to these forms, which, as intellectual beings, we recognise as higher. But physics deals with matter in isolation from these higher forms, abstracting from all characteristics specific to life or intellect. It is not, however, this restriction to dead matter which leads physics to neglect the analogy of being and the doctrines deducible from it. These doctrines apply equally to dead matter, in which, for example, change is still subject to the four types of cause. The roles of these four types may seem more difficult to define in natural changes of dead matter than in the working of artifacts; but when it is remembered that Thomist philosophy has demonstrated that God exists, and creates and conserves the world, the difficulty subsides. God being pure Act, communicates being to dead matter creating it, therefore He is its efficient cause, and the final cause of all His creation must be God’s glory. And the formal and material causes of dead matter are respectively the form, or principle of order, and the materia which is informed. To say that, as such, dead matter is ordered, is, of course, to assert something like what vast quantities of post-Cartesian philosophy has laboured unsuccessfully to prove; but this failure would seem to result from reliance on the dead world to produce its own credentials, and moreover from a confusion of two very different questions, namely, "Are changes subject to causation?" and "Must changes occur in ways describable by physical laws?"10 Whereas the Thomist conviction of an order, an intelligible order, depends upon a philosophy which rises to systematic treatment of intellectual beings and their causality, and in particular demonstrates the existence of God, whose work of creation cannot possibly be without order. When it is realised
10 Cf. E. Meyerson, identity and Reality, Chap. I.
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that the applicability of the full doctrine of causation to dead matter may be deduced from the fact of creation, the difficulties in our knowledge of its application, which compel us to be agnostic on many points,11 no longer cast doubt on the fact of the application itself. It is evident, then, that a definition of modern physics must take account of some restriction besides the restriction to the study of dead matter. This we shall show to be the restriction to what is measurable.
In ordinary Thomist terms, the kingdoms of "physics," mathematics and metaphysics are distinguished according to three degrees of abstraction,12 according to their freedom from matter. It would be pardonable if the unwary were to gain the impression that Thomism separates physics and mathematics. However, the first degree of abstraction covers not only modern physics but all natural sciences and also philosophy of nature; and the applicability of mathematics to empirical data is not denied. We have seen how the standard method of physics is metrical observation. For this reason, the use of functional relations and mathematical deduction is integral to modern physics. In the phrase of Maritain, modern physics is " formally mathematical and materially physical "; it is an intermediate science of the type conceived by S. Thomas.13 It is tied to matter because its empirical data are derived from material observation; it is dependent upon mathematics for the formulation and testing of its interpretatory scheme. It is the use of mathematical deduction which alone makes possible any attempt at the unifying of empirical generalisations, and frees physics from being a mere catalogue of experimental data. And it is this mathematical element, integral to modern physics, which gives rise to the apparent divergence of physical concepts from
11 Cf. Section II.
12 Abstractio formalis, that is—which is an important point, because abstractio totalis is the only kind of abstraction familiar to students outside the Thomist schools. Cf. Maritain, Degrees of Knowledge, p. 47. Moreover, the objects of all these degrees of abstraction are used in senses unfamiliar to many non-Thomist philosophers.
13 Degrees of Knowledge, pp. 52, 53, 79; cf. 56, 168, etc.; Rideau, op. cit., pp. 12, 13, 24.
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Thomist principles; and harmony is restored very simply when it is recognised that the use of mathematics results from the fact that physics examines dead matter only through measurement, and is limited thereby.
II
This description of physics vis-à-vis Thomist philosophy is perhaps best developed with reference to a few selected Thomist doctrines; for instance, causation, the analogy of being, and our knowledge of essences.
It is held on philosophical grounds that the order in dead matter is subjected to four kinds of cause. In the physical scheme, however, these are not mentioned, and are not in fact distinguishable; an interaction between two physical entities is described by combination of certain equations representing the entities and any general laws involved; and this mathematical process does not discriminate between the material cause, the formal cause, the immediate final cause, and the instrumental efficient cause. The mathematical type of ground-consequent relation is in fact made to symbolise the real cause-effect relations; deducibility to symbolise causality. Since for physical interpretation there is only this one type of relation available, we cannot expect to find the several types of cause dealt with separately, nor to be able to identify them in a change considered physically. Again, with regard to analogy, we cannot expect (since physical entities, such as atoms, have to be representeed in algebraical terms) that atoms of the same kind shall be represented as members of a hierarchy of perfections; from the physical point of view they are identical except in the numerical values of certain variables. (Entities of different kinds are represented physically as differing only in the number and arrangement of their constituent parts, or in the case of "ultimate particles" by the magnitude of charge and mass.)
In regard to our knowledge of essences in physics, the position is clear up to a point: physics does not give us adequate definitions of the essences of dead matter. We cannot have a knowl-
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edge of the nature or natures of dead matter similar to that which we have of the specific nature of man, nor yet similar to that lesser understanding which we have of the specific nature of an animal or vegetable substance.14 Certainly we reach our physical scheme by a route similar to that which may lead to adequate knowledge of our essence. A physical entity is accessible through its interactions with others,15 from which a picture of more fundamental characteristics is built up, and finally (if possible), there is constructed a thing of reason with an objective foundation (ens rationis cum fundamento in re). This looks similar to our approach towards adequate knowledge of an essence: by means of observation of contingent accidents (events, interactions), we reach a knowledge of the necessary accidents or properties, and thence of the essence which is their raison d’être. For instance, we recognize from man’s accidents the properties of the specific nature of man (liberty, morality, sociability, religion, etc.), and hence the specific difference, namely rationality, which determines these properties and from which they may be deduced. In the case of physics, however, every step away from the actual experimental data renders our constructions less immediately intelligible; 16 we can use vague analogies like muscular force and mental energy, but they are misleading, and the variables in terms of which the constructions of the physical scheme are ultimately defined (such as energy, charge, mass) are certainly not intelligible to us in the same degree as rationality in man, or immanent activity in plants. What seems uncertain is whether the entia rationis of physics are inadequate definitions of real essences, or definitions (adequate or inadequate) of accidental concretions.17 The nature of their relation to their fundamentum in re is not altogether clear. But in either case it seems clear that physics "cannot provide the natural prolongation of the ontological explications supplied by philosophy." 18 There is no escape from the relative non-intelligibility of dead matter; when we
14 Cf. Adler, loc. cit., pp. 114, 115.
15 Cf. Rideau, op. cit., pp. 41, 42.
16 Cf. Rideau, op. cit., pp. 25, 29.
17 Cf. Adler, loc. cit. (III).
18 Cf. Maritain, op. cit., p. 81; cf. Chaps. I and III, passim, esp. pp. 196-7.
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try to penetrate its specific natures by the only possible method open to physics, namely by an organised survey of their properties via the quantitative ground of accidents, we find that our interpretations have only the status of entia rationis, which are not directly intelligible because they involve variables remote from observation, and whose relation to their real ground (fundamentum in re) is not well understood. And with regard to substance (even supposing for simplicity that we held that there was only one essence informing dead matter), we should still have the greatest difficulty in deciding which of our physical entities represent dead substances, and which accidental concretions. Individuality in physics is remote from the philosophical conception of substance.19 Any physical entity is part of a larger physical system from which it is separated only in thought, for all the entities of the universe interact to some degree, and it seems to be a matter of indifference, fundamentally, whether the interaction of two atoms is occurring while they are at a great distance apart or when they are so close as to form a molecule; physically speaking, certain variables will have altered and certain new accidents will have appeared in consequence. But it should be evident from the foregoing that none of this presents any philosophical difficulty.
III
Several other characteristic notes of modern physics may be treated as direct consequences of the use of mathematical entia rationis; for instance, its "space," "time," and "determinism."20
"Space" as known to us in ordinary experience 21 is replaced by systems of coordinates. "Time "in physics is not the measure of motion as in the Aristotelean definition, and has not the characteristics of la durée; only a comparison of motions more and less regular remains, a variable which is itself measured.22
19 Cf. Rideau, op. cit., pp. 40-4i.
20 Cf. Rideau, op. cit., pp. 33-60.
21 On real space see Degrees of Knowledge , pp. 201-202.
22 On real and physical time see Maritain, Theonas, pp. 61-101
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"Determinism" in physics simply denotes the view that dead matter is "mathematically intelligible "; that is, that the order which informs dead matter is symbolisable by mathematical relations and gives rise to experimentally~accessible functional relations; and this also is remote from philosophical determinism.
And several major advances of this century are of interest as being consequences of certain limitations imposed upon observation by the nature of things (and not by mere experimental difficulties). These are the theory of relativity, the "principle of indeterminacy," and Dirac’s principle of superposition of states.
The theory of relativity completes the scheme of classical mechanics, which applies with great accuracy to phenomena on the ordinary scale. Because of the finite velocity of light, which nevertheless provides the quickest signal of a physical event, we cannot detect an event at exactly the moment it happens. Moreover, observers with different positions, velocities and accelerations relative to the system in which the event occurs, will observe the event after different lapses of time. The contribution of the relativity theory is to make this clear, and to formulate relations between the times and distances involved, such that the description of the event is independent of the particular frame of reference of each observer. The connection of the "spatial" and "temporal" measurements turn out to be such that certain equations which formerly contained the square of the distance coordinates (x2, y2, and z2) must now contain also — t2, where t is the time coordinate. The use of these equations in four variables is an algebraical device, whose purpose is simply to insure that the description of an event shall be independent of particular conditions of observation. The statement that it represents a new concept, "four-dimensional space-time," although intelligible in physics, has proved a grave danger to sound thinking. Again, it is possible to obtain a four-variable expression analogous to that for the curvature of a three-dimensional solid, and this expression is important because it determines the energy of a particle at a given point in space and instant in time; in physics it may safely be called
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the "curvature of space-time," but such terminology is misleading in the extreme when it is used in ordinary speech without translation. The looseness of such language, when used outside the technical vocabulary of physics, is quite extraordinary; it has contributed largely to the unnecessary mystery about relativity, and must surely be partly responsible for the astonishing looseness of thought exhibited by those who have come to believe that space and time are not " really " distinct and that efforts to form a mental or even pictorial image of a world of four dimensions (all on equal footing!) can serve a useful purpose. No philosophical conclusions can in fact be drawn from the success of the relativity theory, except possibly some confirmation of the views on physics given above.
The "principle of indeterminacy" is one of the non-classical principles necessitated by the success of the quantum theory and of the greatest importance in phenomena on the atomic scale. The historical starting-point for a number of new principles was the fact that numerous experiments gave results incompatible with the older view that energy is a continuous variable, but easily interpreted on the view that energy is only transferred in discrete amounts; or more accurately, that we cannot, as in the classical view, regard the disturbance of the any transfer of energy except in these discrete amounts (quanta). From this it results that in order to observe a physical system, which can only be done by an interaction with another system such as a measuring instrument, we must disturb the system to at least a certain irreducible extent. We cannot, as in the classical view, regard the disturbance of the system as (in principle) capable of being reduced indefinitely. This limitation on our observation has important consequences. We cannot, in principle, observe with complete accuracy both the position and the velocity of any particle; this is an obvious consequence of the disturbance due to observation. If we observe the position more accurately, the velocity is correspondingly less accurately observable, and vice versa. With regard to physical law in general, this means simply that the data by which physicists formerly believed that they could forecast the
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future of a physical system are unattainable; we could not, in principle, forecast the result of an experiment with complete accuracy, because our observations can never tell us exactly the conditions of experiment;23 we have to express predictions in the form of statistical laws, stating the probability of such and such a result. What possible influence can this have upon the theory of causality? Yet extravagant pseudo-deductions about a "failure of causality" have been made. We can only say that the belief that this "principle of indeterminacy" (a better name would be "principle of inexact observation ") has any metaphysical implications seems to arise merely from a facile attempt to draw philosophical views on causation and order from physical science. And the attempt to deal with human freedom on this basis 24 seems to commit most of the errors possible in the philosophy of science.
Dirac’s "principle of superposition of states"25 is an interesting outcome of a special restriction upon observations. A series of discoveries has established very peculiar analogies between "radiation" and" matter." It is established that each of these may affect observing instruments either in ways interpreted as characteristic of corpuscles (which may be defined as manifestations of energy localised in a small volume and capable of local motion with finite velocity), or in ways interpreted as characteristic of waves.26 According to the type of experiment performed on it, the same physical system appears to manifest itself either as a corpuscle or as a wave, as continuous or discontinuous; and it seemed that two distinct entia rationis were needed to symbolise the same fundamentum. In view of the status of the interpretatory entia rationis there would seem to have been nothing anomalous in this situation from a philosophical point of view. The two conceptions have been related by the wave-mechanics, which interprets the wave-function as defining the probability of finding the energy localised corpuscle-
23 Cf. Dingle, Nature (1935), Vol. 135, p. 677.
24 Eddington, Nature of the Physical World, Chap. XIV.
25 Dirac, Wave-mechanics, Chap. I.
26 Cf. Rideau, op. cit., pp. 29-32.
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fashion at any given point; none the less, the necessity of superposing the wave and particle models in order to describe all the phenomena remains as a further example of the restrictions placed upon physics by its method of metrical observation.27
Indeed, it may be said generally that the leading principles of modern physics accord admirably with the way in which the empirical data are obtained (namely, by metrical observation). This was not the case when physics still used such concepts as solidity, quantity of matter, absolute motion, and "forces" pictured as similar to muscular effort; it is in fact a happy result of the advances of the last thirty years in physics, and one for which philosophers may legitimately be grateful.
* * *
The conclusions of this article may now be summarised. Modern physics uses experimental methods, which are confined to metrical observation, and accordingly its subject-matter is the measurable aspects of non-living material nature. The inductive method cannot provide its own credentials, and the validity of physical conclusions rests upon a philosophy which can show that order is to be expected in dead nature; in Thomism this may be deduced from the doctrine of creation. Modern physics goes beyond the formulation of laws, and constructs a unified interpretatory scheme, to which the use of mathematics is integral; consequently it uses mathematically defined entia rationis (the nature of whose relation to their fundamentum in re is not altogether clear) . The restriction of physics to the quantitative aspects of dead matter causes it to seem at variance with Thomist philosophy in important respects. Some modern philosophers would seem to have been influenced by the rise of physical science in such a way that they have tended to restrict their philosophy too much to the same subject-matter as physics, with lamentable results. Consequently, it is of importance that competent Thomists should consider in de-
27 Cf. Maritain, Degrees of Knowledge, p. 109; Dingle, Nature (1935), Vol. 135, p. 515.
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tail the nature of modern physics, the way in which it depends upon philosophy for its validity, the general reason for its apparent conflict with Thomist philosophy, and the way in which harmony is effected, by consideration of the effects on physics of its self-restriction (and the results for Thomism of its own efforts at synthesis). The purpose of this article has been to bring before Thomists the situation, that the study of physics is for many a stumbling-block to Thomist philosophy; the reasons for that situation; and a tentative set of solutions to the various problems. It is to be hoped that those more competent than the author will apply the spirit of the Summa contra Gentiles, and exhibit Thomism as the solution of the many current perplexities arising from the widespread attention to physical science and neglect of philosophia perennis.
E. F. CALDIN
The Queen’s College,
Oxford, England