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The Conceptual Structure of Physics AFOSR 2577 THE CONCEPTUAL STRUCTURE OF PHYSICS LASZLO TISZA TECHNICAL REPORT 409 FEBRUARY 1, 1963 MASSACHUSETTS INSTITUTE OF TECHNOLOGY RESEARCH LABORATORY OF ELECTRONICS CAMBRIDGE, MASSACHUSETTS ------- --l-rrjrmui^ll-^mPlii'tBoX1IXIII1"· ···'(-· The Research Laboratory of Electronics is an interdepart- mental laboratory in which faculty members and graduate stu- dents from numerous academic departments conduct research. The research reported in this document was made possible in part by support extended the Massachusetts Institute of Tech- nology, Research Laboratory of Electronics, jointly by the U.S. Army (Signal Corps), the U.S. Navy (Office of Naval Research), and the U.S. Air Force (Office of Scientific Research) under Signal Corps Contract DA36-039-sc-78108, Department of the Army Task 3-99-20-001 and Project 3-99-00-000; and in part by Signal Corps Contract DA-SIG-36-039-61-G14; and was performed under U. S. Air Force (Office of Scientific Research) Contract AF49(638)-95. Reproduction in whole or in part is permitted for any purpose of the United States Government. I _ _ _ Printed in U. S. A. REVIEWS OF MODERN PHYSICS VOLUME 35, NUMBER 1 JANUARY 1963 The Conceptual Structure of Physics* LASZLO TISZA Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts pedic character and is far beyond the grasp of an individual. On the other hand, the classical method Introduction . 151 of organization according to logical structure exhibits I. Dynamics of a single deductive system ...... 155 II. Intersystem dynamics . .... .... .. .. 158 the simplifying and unifying power of high-level III. Logical integration . .. .. .. .. 160 abstractions. This feature presumably accounts for IV. Mechanics, thermodynamics, and quantum mechanics .................. 163 the appeal of classical physics, which endures even A. Introduction ..... 163 in the face of breakdowns and limitations. B. Classical mechanics . 164 C. From thermodynamics to quantum mechanics. Of course, the unifying power of the classical logi- Quasistatics ................ 166 cal structure is severely limited. The difficulties stem D. Dynamics of structures . 178 E. Physics of organisms . 182 primarily from the fact that this structure centers V. Philosophical Reflections .... ....... 183 around Newtonian mechanics as the basic discipline. The situation was characterized by Einstein as INTRODUCTION follows: HE systematization of the theories of physics "In spite of the fact that, today, we know posi- can be attempted along two different lines. A tively that classical mechanics fails as a foundation classification is either based on the logical conceptual dominating all physics, it still occupies the center of structure, or else follows the pattern of classification all of our thinking in physics. The reason for this of the objects that are of principal interest in the lies in the fact that, regardless of important progress theory. reached since the time of Newton, we have not yet The most important example of the first procedure arrived at a new foundation of physics concerning " is provided by late 19th century physics which is which we may be certain that the manifold of all divided into mechanics, electrodynamics, and ther- investigated phenomena, and of successful partial modynamics. This logical structure, and particularly theoretical systems, could be deduced logically from the program of ultimate unification by reduction to it." classical mechanics, was shattered by the crisis that During the quarter of a century that elapsed since marked the transition from classical to modern phys- Einstein wrote these lines, the discrepancy between ics. At any rate, the practical needs of contemporary the classical mechanical thinking and the formal research shifted the emphasis to the second of the development of physics has further increased. At the abovementioned methods of systematization, within same time there is no decisive advance in the emer- which one speaks of the physics of elementary parti- gence of a new comprehensive foundation that can cles, nuclei, molecules, fluids, solids, plasma, and be accepted with assurance. stars (to mention only some of the most important The purpose of this paper is to describe a new divisions). Further subdivisions have been considered technique of logical analysis that is to bring about a which depend on the expanding range of knowledge. more harmonious relation between conceptual think- Thus, one has not only the physics of semiconductors ing and formal developments. However, this is to be and masers, but also the physics of elementary parti- achieved within a program the scope of which is cles in various ranges of energy. much more modest and manageable than the one Both methods of organization satisfy specific and hinted at by Einstein. important needs. On the one hand, the classification We propose to sort out and improve the logical by objects of interest is indispensable for making structure of the existing, empirically verified theories. specialized knowledge possible. However, the totality The establishment of a new foundation is the ex- of physics presented in this fashion has an encyclo- pected outcome rather than the prerequisite of this * Supported in part by the U. S. Army Signal Corps, the procedure Air Force Office of Scientific Research, and the Office of Naval Research; and in part by the U.S. Air Force (Office of Scien- 1 A. Einstein, J. Franklin Inst. 221, 349 (1936). Reprinted tific Research, Air Research and Development Command) in A. Einstein, Ideas and Opinions (Crown Publishers, Inc., under Contract AF49(638)-95. New York, 1954), p. 300. 151 ----------_ - - -_ _I___Illl -"--·--l--"-·Lsr·-i· 1-_ ^1 _ 152 LASZLO TISZA The problem is to take advantage of the use of in the existing experimentally supported theories. high-level abstractions while minimizing the risks We abandon the traditionally static, not to say inherent in their use. Successful abstractions have a dogmatic, relation between postulational basis and predictive value of unexpected scope that greatly system. In the present approach the basis is tentative exceeds the range of their original empirical founda- and subject to change if this leads to an improvement tion. This situation often produces an unjustified of the system in accounting for experimental facts. confidence in the absolute validity of the theory. Yet This feedback from system to basis leads to the dy-, not even the most perfect agreement between theory namic, evolutionary adjustment of the system to a and experiment, extending over a wide range, pro- widening range of experience. Instead of assuming vides a guarantee against the appearance of an essen- that deductive systems have to be perfect in order' tial disagreement as the range of experience is ex- not to collapse, the present method of analysis deals tended even further. The resolution of such disagree- with imperfect systems. In fact, one of the tasks of ments may require the reconceptualization even of the method is to locate and eliminate imperfections. those theories that have been confirmed by experi- In view of this situation, we shall refer to this method ment. as dynamic logical analysis, or the dynamics of de- As a protection against the ossification of success- ductive systems. ful theories, we propose to make the connection Section I of this paper contains a survey of the between basic assumptions and experimental pre- dynamic principles for the construction of deductive dictions sufficiently manifest, in order to facilitate a systems. These principles are not new, they have continued readjustment of the basic assumptions to been developed in great detail in mathematical logic, the expanding range of experience. The use of de- and the empirical aspects of deductive systems have ductive systems is an important device for achieving been investigated within logical positivism. The this goal. novelty of our presentation is therefore only a matter The basic disciplines of classical physics are indeed of selection and emphasis, and, last but not least, the organized as deductive systems. However, during the contention, and, we hope, the demonstration that 19th century when the three major classical disci- these principles are of practical use. plines assumed their definitive form, the nature of The actual construction of physically relevant de- deductive systems was still very incompletely under- ductive systems along these lines is, of course, a stood. rather tedious enterprise. However, two instances The modern conception of deductive systems to be have been actually produced thus far. First, the used in this paper is in some of its main aspects macroscopic thermodynamics of equilibrium,2 briefly diametrically opposed to the classical one. Tradition- MTE, and the statistical thermodynamics of equi- ally, deductive systems are used to organize knowl- librium,3 briefly STE. edge that is already well substantiated. It is deemed The axiomatizations of these well-known theories essential to start from a basis that is safe from any demonstrates the fact that the application of modern emergency that might call for its revision. Of course, logical principles leads to a considerable restructur- the origin of this reliable basis was an ever unsolved ing-even of classical disciplines that seemed to have mystery. For existing systems that have been ac- assumed a fairly rigid pattern. cepted as entirely dependable, the problem seems to It is an important insight
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