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Physics and natural philosophy

1951, Physics Today

For nearly a century we physicists have complacently thought of ourselves as being the philosophers of nature. While the biologists and astronomers expanded their interminable classifications and the chemist did heavens-knows-what with his grubby beakers, we were, in our own estimation at least, constructing rational pictures of the universe aided by artfully chosen experiments. It is true, of course, that at times these self-consistent and rational pictures did not agree with each other; but, when this happened, we became true philosophers in the Greek sense and in a mist of polemics and sophistry demonstrated that nothing could be more rational than the disagreement which was only apparent after all.

Physics and natural philosophy John R. Van Wazer Citation: Physics Today 4, 6, 18 (1951); doi: 10.1063/1.3067250 View online: http://dx.doi.org/10.1063/1.3067250 View Table of Contents: http://physicstoday.scitation.org/toc/pto/4/6 Published by the American Institute of Physics In spite of their many spectacular works, the present article suggests, physicists should not rest too comfortably on their laurels. Physics is not the only field concerned with understanding nature. PHYSICS By John R. Van Wazer Figure 1. B. The Secondary Sciences 1. Theory of gravitation 2. Theory of action of pressure and heat in changing the dimensions and state of a body 3. Theory of radiance 4. Electricity and magnetism For nearly a century we physicists have complacently thought of ourselves as being the philosophers of nature. While the biologists and astronomers expanded their interminable classifications and the chemist did heavens-knows-what with his grubby beakers, we were, in our own estimation at least, constructing rational pictures of the universe aided by artfully chosen experiments. It is true, of course, that at times these self-consistent and rational pictures did not agree with each other; but, when this happened, we became true philosophers in the Greek sense and in a mist of polemics and sophistry demonstrated that nothing could be more rational than the disagreement which was only apparent after all. A good example of the lordly mien of the physicist is found in the Ninth Edition of the Encyclopedia Britannica, which is usually considered to be the most scholarly of all the editions. In an article entitled Physical Sciences, J. Clerk Maxwell set up the following general classification of science —in which all disciplines except physics were completely ignored. In a similar but considerably more jocular vein, N. F. Mott chose to define science as being nothing but "physics and stamp collecting" when he was the after-dinner speaker at the last Chicago meeting of the American Physical Society. Now, at the risk of being considered a heretic, I would like to say that, by its own criteria, physics is far from being the Big Cheese in natural philosophy in spite of its success in pioneering new fields. But what are its own criteria? Well, in the present stage of the development of physics the workability of a given concept is usually thought to be a reasonable measure of its value. That is to say, the closer the quantitative fit between theory and experiment and the greater the number of diverse experiments predicted and fitted, the better the theory is. Let us look at some cases: The mathematical theory of elasticity, which occupies a prominent position in the field of mechanics, has been of little value in precisely describing the elastic behavior of most materials. Its greatest application has been in the field of structural engineering where a "safety factor" of several hundred percent is usually employed. Within such a wide latitude the theory has enjoyed considerable success. A. The Fundamental Science of Dynamics 1. Kinematics 2. Statics 3. Kinetics 4. Energetics John R. Van Wazer is a senior scientist of the Monsanto Chemical Company in Anniston, Alabama. Since receiving his PhD from Harvard in 1942, he has been active in both physics and chemistry. A member of the Society of Rheology, his principal interests have been concerned with rheology and the chemistry of phosphates. 18 PHYSICS TODAY 19 NATURAL PHILOSOPHY Figure 2. But, you may complain, the brief discussion given above is unfair to the theory of elasticity which is not concerned with real materials but describes ideal elastic bodies. And now we come face to face with one of the biggest and best pieces of legerdemain in the history of philosophy—the ideal physical entity. Historically, the first of the presentday "ideals" was probably the ideal gas. When Boyle studied the relationship between the pressure and volume of a confined gas he generalized from his rough data that pv = constant. Later investigators found that this relationship and its more complete form, pv = RT, did not offer a very good fit to experimental data so it was first assumed that one kind of gas, the permanent gases, behaved according to the law and another kind, the vapors, did not. Later more complex equations with several adjustable constants were developed; but the beautiful simplicity of pv = RT was never forgotten and this simple equation is still much more popular than its competitors. The gas it describes is the non-existent ideal gas. And so it goes, the ideal solid, the ideal gas, the ideal thermodynamic system with its concept of ideal reversibility, the ideal liquid, the ideal solution and so on ad infinitum in every branch of physics in which matter must be taken into account. The apparent exception is shown by the field of electricity in which the term ideal is seldom used. Instead the physical operations are carried out with circuit components (resistors, capacitors, etc.) which are carefully designed and manufactured so JUNE 1951 as to fit certain defining equations such as Ohm's law. Thus we do not speak of ideal electrical components but rather single out the non-ideal ones, as is demonstrated by the term non-Ohmic resistors. This business of emphasizing the ideal and excepting the non-ideal can be very misleading. In the case of internal friction in fluids, the ideal or Newtonian liquid had such a hold on men's minds that glaring departures from the ideal were completely overlooked for about SO years of precise measurement. Even such worthies as Lord Kelvin went through complicated mathematical gymnastics in order to avoid admitting that non-Newtonian flow existed. Now that non-Newtonian flow is a generally accepted fact it is still common practice to report experimental data in terms of equivalent coefficients of viscosities even though these coefficients may vary manyfold with changes in the velocity of flow and other experimental variables. Many of the data reported in this manner are completely unintelligible and do not afford even enough information to allow the corresponding experiment to be reproduced. The divergence between fact and ideality is indeed so great in this field that it has driven a well-known English rheologist, G. W. Scott-Blair, from the realm of physics into a new discipline which he has named psycho-physics. But, you may say, physics may be as bad as all this but yet no other field of natural philosophy has done any better. Inadequate as it seems, physics may still be the most satisfactory example of man's attempts to rationalize nature. 20 This conclusion, however, is far from true. Both in simplicity and elegance of presentation organic chemistry is far in the lead of physics. Moreover it works without the need of any idealizations. In broad outline organic chemistry can be described as follows: Using the concept of a fixed number of covalent bonds for each atom (four for carbon, two for oxygen, one for chlorine, one for hydrogen, and so forth) and employing practically nothing but melting point, boiling point, color and odor for characterizing his creations, the organic chemist has prepared millions of different substances, many of which are believed to have had no previous existence in nature. By treating the atoms as building blocks and building up (synthesizing) and breaking down (degrading) combinations of atoms the organic chemist was able to arrive at a logical picture of his molecular structures. Instead of employing mathematics as his descriptive medium, the organiker draws two dimensional diagrams or maps of the molecules. In Figure 1 several such diagrams are shown. When the molecule becomes extremely complicated, the symbols for the atoms are usually omitted and a simpler diagram, such as is given in Figure 2, is used. The most amazing thing about these molecular diagrams is that as physical methods, such as x-ray diffraction, for determining molecular structure were developed and applied, it was found that the relative arrangements of atoms based on the rationalization of the simple chemical operations agree with the physically determined structures. And not only were the atomic arrangements concordant but even the relative sizes of the atoms were found to have been correctly derived from a chemical effect known as steric hindrance. This effect depends on mechanical interference between the parts of a molecule and thus a large atom which causes more interference than a small one can be singled out. If an organic chemist is given a diagram or systematic name of a molecule he can prepare it or, in exceptional cases, show why it cannot be made. The notation describing organic molecules is direct and explicit and the equivalent substance can be produced. Therefore, in my estimation at least, organic chemistry rather than any of the branches of physics is the outstanding example of the successful rationalization of natural phenomena. Since the introduction of quantum theory, physicists have been proud of their broad-mindedness and are eager to show that a given physical phenomenon may have several equally credible theoretical explanations. It is now felt that a large amount of theoretical work is merely the setting up of models of the real system (if such a word as real is even admissible) or the laying out of a map which enables one to find his way about the real system. Thus we have the concept of the invariance of a system to its model. Presumably a model is well chosen when minor changes in its structure do not affect the precision with which it can be fitted to experiment. Using this criterion for the suitability of a model the claim could be made that psychology and not physics offers the most suitable model in natural philosophy. Although their descriptions of the same occurrence may differ so greatly as to be practically unintelligible to a member of a different school, the various schools of psychiatry have by the application of their diverse theoretical concepts achieved important and singularly uniform experimental results. By the use of any of the psychiatric theories it has been shown possible to remould a number of rather fundamental characteristics of the individual human personality. The one feature that the various theories of psychiatry have in common is a persistent focusing of attention on a single personality characteristic, which can apparently be selected practically at random. For example the Freudian school focuses its attention upon sexual behavior and the Adlerian school upon childhood impressions. This means that all of the observable variables which go together to make up the nebulous and illdefined function called the personality depend on each other in such a manner that the form of the entire function can be altered by manipulation of any one of the variables. Although this generalization in the field of the social sciences is probably a reductio ad absurdum of the argument that a number of different and equally useful models is desirable, it could also suggest that physics has again come out second-best in terms of its own criteria of excellence. In this brief and thus oversimplified essay on the role of physics in the philosophy of nature, I have tried to show that physics is but a small part of the whole. If this conclusion is correct, we should feel humble but not vanquished, for the tools of the physicist are very powerful and can yet open many unexplored realms in the philosophy of nature. Such recent developments as cybernetics and operational research show that physics can contribute much towards some of the hitherto unrelated branches of natural philosophy and, of course, present studies on subnuclear structure demonstrate that exploration within the accepted domains of physics is by no means limited. PHYSICS TODAY








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