The revolution in physics at the end of the nineteenth and the beginning of the twentieth centuries was a significant event in both the history of science and the history of philosophy. Various schools of philosophy have interpreted this event differently. Naturally, this is of concern to Marxist philosophy. Based on relatively rich original sources, this article analyzes the historical role, philosophical origin, and end result of two schools in this revolution, the Mechanical School and Critical School. The author offers an interpretation which differs from the traditional one, especially with the respect to the Critical School. This paper is intended to promote academic discussion, to further explore the philosophic significance of this scientific revolution, and to enrich teaching and research in natural dialectics.
From the beginning of the eighteenth century, physicists came to regard Newtonian mechanics as the research program for all fields of physics, to the extent that it became the supreme authority and ultimate standard of scientific interpretation. Until the end of the nineteenth century, physicists almost universally believed that all physical phenomena could be explained from the perspective of mechanics.
However, the end of the nineteenth century witnessed a continuous stream of new experiments and discoveries which severely shook the foundations of physics, leading to a crisis. Under such circumstances, some physicists came to doubt the universal application and absolute reliability of the classical theory. One after another, they began to criticize the basic concepts and principles within classical mechanics and to challenge the dominant mechanistic viewpoint. Thus, diversity replaced unity, and physicists formed schools which differed from each other even in their basic guiding ideologies. Some scholars have divided them into the Energetic School, the Mechanical School, and, intermediate between these, the Critical School. Others have identified them as the Realist and Symbolic Schools. I would like to classify them into the Mechanical School and the Critical School, based on the different attitudes toward classical mechanics.
Some previous publications in the Soviet Union, Eastern Europe, Japan and China have tended to overemphasize the Mechanical School and belittle the Critical School, even entirely denying its role in the development of physics. I think this is not entirely accurate. This article undertakes a preliminary examination and discussion of this issue, based on the historical context and relevant original sources.
I. Two Historical Roles
What role did each of these two schools play at the turn of the century during the crisis in physics and the beginning of the revolution? First, it must be noted that the Mechanical School, which possessed an absolute superiority in numbers, made indelible contributions to the development of classical physics. An early representative of this school, G.R. Kirchhoff, did extensive work in electricity and spectral analysis. In 1859 he proposed the law of cavity radiation, which was an important milestone in research on heat radiation. H. von Helmholtz made outstanding contributions to thermodynamics and electricity. In 1847 he published an important book, Uber die Erhaltung der kraft, about energy conservation and conversion. J.C. Maxwell contributed to thermodynamics, optics, molecular physics, the theory of the characteristics of fluids, etc. In particular, he proposed the distribution law of molecular motion and the law of equipartition of energy in 1859, and the electromagnetic field equations in 1864, which formed the theoretical foundations for statistical mechanics and electromagneticsm. L. Boltzmann, who was still active in physics at the turn of the century, also greatly contributed to the development of kinetic theory, thermodynamics, and statistical mechanics. His probabilistic explanation of the second law of thermodynamics is well known. Lord Rayleigh made achievements in acoustics and vibration, optical theory, heat radiation, etc. Lord Kelvin, a veteran in physics, contributed tremendously to theoretical and experimental investigations of heat and electricity. Lorentz devoted himself to research on electronic theory from 1875. Electron Theory, which he published in 1909, was the last great edifice of classical theory. Obviously, the contributions of the Critical School to classical physics cannot be compared to those of the Mechanical School. The latter developed classical theory to perfection, inadvertently providing the necessary conditions for the coming revolution in physics.
However, the Mechanical School also inherited “the fanaticism that reduces everything to mechanical motion.”1 In 1847 Helmholtz asserted, “We eventually find that all questions related to physics can be reduced to gravitation and repulsion…The mission of physics ends with the simplification of all natural phenomena into force. ”2 On the one hand, Maxwell shook the belief that mechanics is the ultimate foundation of all physics with the theory of electromagnetism. On the other hand, they tried every means to stuff their theory into the framework of mechanics.
By the end of the nineteenth century, experimental evidence, such as Michelson’s experiment, the specific heat of polyatomic gases and solids, the photoelectric effect, black body radiation, atomic spectra, and particularly the discovery and research on radiation after 1895, had profoundly shaken the whole foundation of physics. Nevertheless, the Mechanical School still cherished the basic concepts and principles of classical theory within the “treasure box” of “absolutes,” claiming that they are an unalterable “sacred heritage.”3
The celebrated Kelvin was keenly interested in the construction of mechanical models of the ether. In 1884 he proclaimed, “I never satisfy myself until I can make a mechanical model of a thing.”4 In 1890, he suggested that electrical effects are caused by the translational movement of ether, that magnetic phenomena can be explained by the rotation of ether, and that light is the result of wavy vibrations within the ether. In 1907, in the last public appearance before his death, he still supported the view that every cubic millimeter in space contains a thousand tons of ether mass. Kelvin was often suspicious of new discoveries and theories in physics and was particularly opposed to the theory of the transmutation of elements. In August of 1906, at the age of 82, he stubbornly insisted that radium originally contains helium and therefore the production of helium from radium cannot justify the theory of the transmutation of elements, a theory cleverly fabricated solely for the purpose of explaining the properties of radium. He also attributed the energy of the sun to gravity, opposing explanations which referred to transmutation.
Although Lorentz actively participated in frontier research in several areas of physics at the turn of the century, he tried very hard to revise old theories and to mediate between mechanics and electrodynamics without violating the framework of classical theories. However, Michelson’s 1887 experiment rejected Fresnel’s stationary ether theory, a prerequisite of electromagnetic theory, thus attacking its mechanical foundation. Lorentz was upset and gloomy, writing in a letter to Rayleigh in 1892, “I simply don’t know how to get rid of this contradiction, but I still believe that if we have to discard Fresnel’s theory,…we will never have an appropriate theory.”5 In the same year, he proposed the contraction hypothesis to resolve the dilemma. In 1904, following Poincare’s suggestion, he obtained the law of corresponding states applicable to effects at all orders and introduced the mathematical transformations which are named after him. Lorentz’s theory was very similar in mathematical form to the special theory of relativity, but it differed fundamentally in physical explanation, lacking a thorough redefinition of traditional concepts of space and time. Even in his later years, Lorentz continued to believe that the ether concept possesses certain advantages. M. Born recalled, “when I visited Lorentz several years before he died, his suspicion of relativity remained unchanged.”6 According to S.Sakata’s recollection, Lorentz, facing the new concept of waveparticle duality, despairingly lamented,
People nowadays suggest ideas which are just the opposite of yesterday’s. Thus, there’s no criterion for truth. No one knows what science is. I really regret that I didn’t die five years ago, before these contradictions appeared.7
other representatives of the Mechanical School behaved similarly. Even in 1902, Boltzmann still publicly asserted, “Mechanics is the foundation on which the whole edifice of theoretical physics is built, the root from which all other branches of science spring.”8 Rayleigh carefully analyzed the contradictions between gaseous specific heat experiments and the classical energy equipartition theory. He pointed out that experiments destroy the theory’s “simplicity of calculation.” At the same time, he admitted,”it seems that the hope is to avoid destroying the simplicity of this widely accepted conclusion, energy equipartition.”9 Unwilling to break the bonds of the old framework, he also tired hard apply the energy equipartition theory to the ether model in order to explain black body radiation. Even at the 1911 Solvay conference, he maintained a negative attitude toward the eleven-year-old quantum theory.
The representatives of the Critical School are E. Mach, H. Poincare, P. Duhem, W. Ostwald, and Karl Pearson. Their attitudes differed completely from those of the Mechanical School, and the appeared very early as reformists.
In 1883 Mach published his historic work The Science of Mechanics: a Critical and Historical Account of its Development. This book shows that even before a large number of the new experiments and new discoveries which shook the foundations of classical physics appeared, Mach had already realized the limitations of the theoretical framework of classical mechanics. (In fact, as early as 1871, in his speech ‘The History and Origin of the Law of Energy Conservation,’ he had already presented the basic ideas which later appeared in the book.) Adopting a skeptical empiricist approach, he criticized classical mechanics from the point of view of philosophy and logic. As Einstein later noted, Mach “excellently expressed ideas which at that time had not become public knowledge among physicists.”10
The best known section of Mach’s book is a criticism of Newton’s concept of absolute time and space. Mach wrote, “Time is an abstraction. We rely on changes of matter to reach such an abstraction.” So-called absolute time, which is irrelevant to changes in matter, cannot be related to empirical observation. Therefore, “it has neither practical nor scientific value.” It is only “an absolutely useless metaphysical concept.”11 For the same reason, absolute space and absolute motion which are irrelevant to anything else are also “purely the products of thinking and rational constructs. They cannot be derived from experience.”12 Mach explicitly stated, “If we stand on the facts, we find that we know only relative space and relative motion.”13 “It’s absolutely unnecessary to return to absolute space because the frame of reference, in any situation, is always determined relatively.”14
In the chapter ‘The Relation of Mechanics to other Departments of Knowledge,’ Mach concentrated on criticizing the mechanical viewpoint, asserting that people have learned from their predecessors a bias, mistakenly regarding the real world as a mechanical machine. As a matter of fact, mechanical knowledge is not necessarily the basis for knowledge obtained gradually later on. When more and more facts are discovered and classified, a totally new concept applicable to universal fields will be developed.”15 Mach argued that mechanics does not have the privilege to place itself above other disciplines. “It is a prejudice to regard mechanics as the basis of other branches of physics or to claim that all physical phenomena should be explained from the perspective of mechanics.”16 At that time, only Mach explicitly challenged the mechanistic worldview. On the eve of the revolution in physics, he proved to be an instigator.
At the turn of the century, Mach’s skeptical attitude, his independent, empiricist position, his powerful criticism of apriorism and the mechanistic viewpoint, and his profound insight into the foundations of classical mechanics produced a strong reaction from Einstein. Einstein frankly admitted many times that Mach “paved the way” for the development of relativity. “I was greatly inspired, directly or indirectly, by Hume and Mach in particular.”17 Einstein also stated,
Mach has greatly influenced natural scientists of our generation with his historical, critical work…I believe that even the self-proclaimed critics of Mach do not know how many ways of thinking they have absorbed from him as unconsciously as they consumed their mothers’ milk.18
Poincare was also engaged in critical research of a similar nature, but his work was based on the considerable experimental data by then available. Moreover, as early as 1895 he proposed the universal necessity of principles such as relativity. In 1898 he was the first physicist to point out the speed of light must be assumed to be a constant to all observers and to study the problem of determining the simultaneity of events at two locations by means of exchanging light signals. In Science and Hypothesis, published in 1902, he once again definitely stated, “Not only have we no direct intuition of the equality of two durations, but we have not even a direct intuition of the simultaneity of two events occurring in different places.”19 At the International Congress of Arts and Science in St. Louis in 1904, Poincare asserted,
According to the relativity principle, the laws of physical phenomena should be the same to fixed observers or to observers moving at a uniform speed. Thus, we do not and will not have any way to identify whether we ourselves are moving uniformly.
Surprisingly, he even predicted,
Maybe we’ll build a brand new mechanics. We’ve succeeded in catching a glimpse of it. Within this new mechanics, inertia increases with speed and the speed of light becomes the insurpassable limit. The original, relatively simple mechanics will still remain as a first degree approximation old mechanics can still be discovered in the new mechanics.20
Poincare was also acutely aware of the crisis in physics. In The Value of Science, published in 1905, he wrote, “I believe that there are indications of a serious crisis” pointing to an “approaching transformation”21 in physics. Poincare thought that the crisis in physics marks “the eve of revolution,” and the forewarning that physics is entering “an even more important stage.”22 Therefore, “be not too anxious. We are sure the patient will not ” die of it, and we may even hope that this crisis will be salutary.23 poincare was optimistic about the future of science. He noted that we already have “the cathode rays, the x-rays, those of uranium and of radium. Herein is a whole world which no one suspected. How many unexpected guests must be stowed away!”24 He firmly concluded, “if the past has given us much, we may rest assured that the future will give us still more.”25
Although the physicists of the Critical School criticized classical mechanics and classical physics, they did not completely reject them. In Mechanics, Mach highly praised Newton’s Principia Mathematica. He argued that, from a historical point of view, mechanical principles are easily understood and their faults are excusable. They are both effective and valuable within a limited period of time and in certain areas. In The Grammar of Science Pearson remarked, “All that modern science will do to the dynamics of Newton and Lagrange will be to define precisely within what limits their application is exact, or with what approximation they may be applied if exactness is not to be admitted.”26
Poincare also emphasized many times that the basic principles of classical physics are of “high value; they were obtained in seeking what there was in common in the enunciation of numerous physical laws; they represent therefore, as it were, the quintessence of innumerable observations.”27 Of course, “it would be necessary to keep a place for them. To determine to exclude them altogether would be to deprive oneself of a precious weapon.”28 Speaking of classical physics, he particularly emphasized,
I do not mean it corresponds to no objective reality, nor that it reduces itself to a mere tautology, since, in each particular case, and provided one does not try to push to the absolute, it has perfectly clear meaning…It will disappear only to lose itself in a higher harmony.29
It is particularly worth nothing that Poincare directly criticized the erroneous claim that the crisis in physics is an indication of “the bankruptcy of science.” He wrote,
The laity are struck to see how ephemeral scientific theories are. After some years of prosperity, they see them successively abandoned; they see ruins accumulate upon ruins. They foresee that the theories fashionable today will shortly succumb in their turn and hence they conclude that these are absolutely idle. This is what they call the bankruptcy of science.
Poincare penetrated to the heart of the matter when he noted, “That kind of skepticism is superficial. They absolutely fall to consider the purposes and functions of scientific theories. Otherwise, they would understand that these ruins may be useful.”30 Thus, the accusation that the Critical School entirely denied the old principles of physics and proclaimed the total collapse of scientific truth is not in accordance with the facts.
It is true that the Critical School denied the reality of atoms and molecules. Needless to say, that’s where they went astray. However, concrete historical analysis of this issue is required. There was no fully reliable experimental evidence regarding the existence of atoms before the 1908 Perrin experiment. Relying on his empiricist philosophy, Mach rejected atomic theory because “atoms…can never be made the object of sensuous contemplation.”31 Poincare merely reserved judgement on this question. He argued that, since the atomic assumption has not been experimentally demonstrated, it cannot be considered either true or false. Moreover, its usefulness as a supplementary assumption is not yet determined. In fact, atomic theory encountered some difficulties in explaining problems concerning the second law of thermodynamics, heat of vaporization, osmotic pressure, chemical equilibria, etc. Ostwald proposed a theory of energetics based on his search for a common foundation which would integrate physics and chemistry. Thus it’s obvious that the major proponents of the Critical School disagreed on this issue. Moreover, to varying degrees, they later recognized their errors. In 1913 Mach admitted that he would have to accept the atomic assumption if it could be shown to be capable of logically connecting observable phenomena which cannot otherwise be connected. After the Perrin experiment, Ostwald immediately publicly admitted his mistake and wrote in the new edition (1909) of Outline of General Chemistry,
I am now convinced…that we have recently become possessed of experimental evidence of the discrete or grained nature of matter for which the atomic hypothesis sought in vain for hundreds and thousands of years… [New discoveries] justify the most cautious scientist in now speaking of the experimental proof of the atomic theory of matter.32
In 1912 Poincare also solemnly stated, “the long existing mechanical hypothesis is now considered to be fully reliable…atomic theory has achieved an absolute victory…the atom…is now a reality.”33
The Critical School also behaved conservatively in some respects in the revolution in physics. Now matter how many mistakes they made, however, during the period of crisis in physics at the turn of the century and the early period of revolution, the Critical School was essentially reformist and promoted the development of physics.
II. Two Philosophical Roots
The quite different reactions of the Mechanical and Critical Schools can be partially explained by their philosophical origins.
The Mechanical School adhered to the cognitive line of mechanistic materialism which, on the one hand, tremendously promoted the development of classical mechanics and classical physics. On the other hand, to a certain degree it became an obstacle to the development of physics because “it did not understand the relativity of all scientific theories, failed to comprehend dialectics, and exaggerated the role of mechanism,”34 thus basically losing its positive value under the particular historical conditions which existed at the turn of the century.
By insisting on the mechanistic viewpoint, the Mechanical School in fact could not follow materialism to its logical conclusion. When a series of new experiments ant the turn of the century sharply contradicted the old theories, the Mechanical School opposed the new discoveries and tried to patch up the old theories rather than rigorously adhering to experimental facts and positively attempting to reform physics. Thus they consciously or unconsciously diverged from the materialist empiricism which is the heritage of natural scientists.
The Mechanical School forgot the everyday worldly origin of the basic concepts and principles within the framework of classical theory. Excluding them from the domain of experience, they placed them on a visionary, a priori peak and claimed them to be sacred and inviolable treasures. In essence, they slipped into a priorism. Under the domination of such an ideology, of course the Mechanical School could not adjust to the development of physics and become reformist.
Strangely enough, it was the Critical School which truly applied the philosophy of empiricism. Although they philosophically gave an opaque and sometimes idealistic explanation of the term ‘experience,’ in scientific practice they insisted on adhering to experimental facts. In The Science of Mechanics, Mach repeatedly emphasized that the essence of nature must not be fabricated by relying on self-evident assumptions. Rather, it should be derived from experience. He pointed out,
Mechanical laws are in fact very complicated, even though they seem very simple on the surface. These laws stop at a stage of incomplete experience and, indeed, can never be completed. They should never be regarded as mathematically determined truths but rather as formulae which not only can be permanently dominated by experience but also need to be so dominated.35
Mechanical principles “cannot be and have never been accepted without being pre-tested by practice. No one can be sure that these principles can be applied to domains which lie outside our experience. In fact, such expansion is useless.”36 Based on his empirical philosophy, Mach examined the basic concepts of Newtonian mechanics one by one. As Einstein later noted, he “pulled them down from their a priori Olympus,” exposed “their worldly origin,” and liberated them “from enforced taboos.”37 Mach’s critical opinions on mechanics led to a heated debate concerning the scientific, historical, and philosophical foundations of classical mechanics and classical physics which exerted a lasting and profound influence.
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