A.B.

Einstein

From New International, Vol.4 No.4, May 1938, pp.157-158.
Transcribed & marked up by Einde O’Callaghan for ETOL.

The Evolution of Physics
by Albert Einstein and Leopold Infeld
Illus. 313 pp. New York. Simon and Schuster. $2.50.

We live in one of the great ages of physics. Our age has been called great in other respects too, but in physics we can be sure. Physical theories developed in the present century have already shown themselves direct agents in the solution of problems of extraordinary difficulty and scope. The power to predict, to control, and to understand have been strikingly extended in the past thirty years. The work of physicists of the preceding three centuries has of course resulted in a much wider range of applications, most of them unforeseen by the theoreticians, but we know that theoretical advances in this field are always followed by developments in engineering and technology and the present age cannot be an exception in this respect. The book under review takes no explicit notice of the material value of physical theories; it is concerned almost entirely with the effect of new experimental results upon the theories of the past. It is thus a history of “pure” physics. Because of this restriction in the scope of the book, the confused philosophical considerations on “reality” are less of a blemish than they would be in a book that was actually concerned with the evolution of physics.

The few broad facts that are clear concerning the nature of physical theory do not suffice to determine a philosophy of physics. Physical theories change with the discovery of new facts and laws, with the developments of new materials and technics, with the ideas of the men who are physicists. The striking changes in general viewpoint that are sometimes called revolutions in physics (there have been at least two since 1904) never negate the observed facts of earlier epochs, but generally describe all the facts formerly known more simply and effectively, at the same time that they make place for newly-discovered facts and relations. Thus physical theories always show essential connectedness with their predecessors and in this sense too, there may be said to be evolution in physical theory.

It has always been the aim of physicists to frame their theories so that a maximum number of true (observable) relationships can be deduced logically from a minimum number of premises or assumptions. It is in this sense that physics has always been and continues to be a logical science. This does not contradict the empirical aspects of the science, which appear always in the deducible consequences and sometimes in the stated assumptions.

Physics has always been a social activity, although this book takes no pains to indicate the important implications of this fact. Like all science it requires the most intense cooperation between contemporaries, and between living physicists and their predecessors. It is a social activity too in that it requires planned support beyond the hope of immediate material return, and in that it is limited and expanded by the state of material culture in which it finds itself. In a smaller sense it is a social activity in that physicists have always written explanations of their work for laymen. Lastly, it is clear to the most casual student of the history of science, that the physics of today is not the result of the work of a string of geniuses, unsupported by anything except their own thinking. It is the result of the steady accumulation of data, laws, techniques, by thousands of workers, of whom a small but important fraction are able to advance general theories for which the layman tends to give them the “credit”.

But these few general facts about the growth of physics (change and evolution, connectedness, logicality, sociality), do not suffice to give us a clear view of the nature or of the importance of physical theory. Einstein and Infeld cannot help us much with this problem, since they refrain from indicating even in the barest outline either what its social uses are, what its applications may be, or what its aesthetic virtues are (e.g., its extraordinary compactness due to its mathematical form).

The book describes, in remarkably clear terms, the rise of the “mechanical” view in pure physics, culminating in the work of Newton. The general program of the mechanists, to describe all the phenomena of physics in terms of force acting as attractions and repulsions between bodies or particles, met with great success in most areas until the beginning of the nineteenth century. The increasing difficulty of explaining the wave-nature of light, and later the facts of electro magnetism, on mechanical bases stimulated physicists to develop the so-called field theories, which are non-mechanical in that the space between bodies becomes as important as the bodies themselves. This development is also explained with exceptional clarity, but purely on the level of physical ideas, out of all reference to use, and to the increasing facilities for research made possible by application of earlier physical theories.

Why is it that a book of such purely intellectual content, requiring from the layman many hours of sustained concentration, is highly praised by all the reviewers, and already is being widely read? Many readers will hope to find the answers to the questions raised above, and most of the reviews do not indicate these lacks. Many have been hearing for twenty years that the theory of relativity could be understood by only twelve men and they now see before them the possibility of joining that select company. The opportunity of listening to one of our indubitable giants of the intellect seems here to be opened to us. This opportunity actually exists, but much of the power of the ideas of the relativity theories is lost in this presentation. The great ideas in physics are great because they summarize compactly and precisely great masses of information. It is not possible to skim the cream off this mass and present it as the theory of relativity without disappointing those who thought, rightly, that “there was more to it than that”. In short, we have here a presentation – well written and carefully worked out – of some ideas which derive their power from their contexts (inside physics and in the engineering world), carefully removed from those contexts so as to make them manageable in a single volume.

This book has then, from a layman’s point of view, three major lacks. It does not show how physics gets applied, or how powerful the older theories were in helping engineers solve their problems, and make their machines. It does not put forth an intelligible philosophy justifying the existence of pure physics. It does not have a bibliography that would help interested persons to read further in the various fields discussed.

It is, however the best book known to the reviewer, for the general reader who simply wants to know what the theory of relativity is like.

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