LETTERS TO THE EDITOR

ON THE QUESTION OF THE PHILOSOPHICAL ERRORS IN MY BOOK “FUNDAMENTAL PROBLEMS OF MODERN PHYSICS”

A. F. Ioffe

A number of articles were published in Voprosy filosofii and in Uspekhi fizicheskikh nauk at the end of 1951 and in 1952 criticizing, from a philosophical point of view, the erroneous propositions in my book Fundamental Problems of Modern Physics, which appeared in 1949.

I consider many of the comments entirely correct. Not only for me, but also for readers of my book, it will be useful to clarify what its errors consisted in and how they should be corrected, and also in what, perhaps, my critics are mistaken.

In what follows I shall be guided mainly by the most complete and systematic analysis of the book by I. V. Kuznetsov and N. F. Ovchinnikov in UFN for September 1951.

It is quite true that the theory of relativity is presented in my book unsatisfactorily both from the didactic and from the philosophical standpoint: the systematic introduction of the observer and of the methodology of measurements in a moving medium, as the justification of the theory in all expositions, including my own, obscures its physical and philosophical content as a teaching about the conditionality of space-time properties by a material medium. This, however, applies to the general theory, which I only barely touched upon.

It must be admitted that the exposition of the special theory of relativity is likewise of a formal character. It is shown how one should use the fact that the speed of light is independent of the state of motion of the system, and, for example, the techniques of radiolocation are cited. It is shown how an observer in one system should observe phenomena occurring in another, moving with a certain velocity relative to the first. But it remains unclear to the reader how processes proceed in systems moving with respect to us: whether or not the dimensions of objects contract in the direction of motion, whether the rate of time inside the system slows down, as many think. How should the law of addition of velocities be understood? What is the physical meaning of the increase of mass as the speed of light is approached?

Instead of all this, it is described what an observer can see in a system moving past him, if the same laws act in it as in our inertial system.

Such a mode of exposition is equally possible for an idealist, interested only in sensations and their systematization, and for a materiali-

... seeing in observations the result of the action on our sense organs or instruments of an external world existing objectively outside us.

For a book which sets itself the task of showing, by the example of twentieth-century physics, the correctness of the propositions of dialectical materialism, such a generally accepted method of exposition, not bristling with references to the observer, is not right.

The authors of the review blame me for “exaggerating” the role of the theory of relativity, which they and some other philosophers consider necessary to call the theory of fast processes. I think that I can rather be reproached for insufficient interest in the theory of relativity, for the fact that to the theory of relativity, created in the twentieth century, just as to the conservation laws, is assigned the role of a check making it possible to discover the fallibility of physical theory, and thereby its creative role is diminished.

Such a character of exposition is to some extent justified by the place of this entire chapter. Its task is to recall the generally known laws of physics and briefly to formulate what will be needed later in the exposition of atomic and nuclear physics. This should have been said at least in the preface.

It was hardly necessary, as some critics demand, in this auxiliary chapter to analyze in passing the gnoseological meaning of the general and special theories of relativity, to repeat Engels’ profound analysis of the law of conservation and transformation of energy, of its connection with the principle of the indestructibility of matter, and to add the basic propositions of philosophy to the laws of physics.

The theory of relativity has in the last year again become an arena of philosophical disputes. Tt. Kuznetsov and Ovchinnikov, as well as some other philosophers, consider it inapplicable either to microphysics or to astronomical problems.

What is meant here? Perhaps the inapplicability of the analogy between gravitation and acceleration for any finite volumes? But after all this analogy is not the theory of relativity. Perhaps the equality of rights of the theories of Ptolemy and Copernicus, advanced by Einstein, is troubling? But after all this is only the result of Einstein’s Machist philosophy, and not of his theory. And the very Ptolemaic system, which leads to countless large velocities of stars, is unacceptable in the theory of relativity, as it is in reality. Or, finally, is it the inability of the theory of relativity to explain the reasonably increasing red shift of lines with distance from our galaxy?

Everyone acquainted with modern physics also knows that precisely in atomic and nuclear physics, i.e. in microphysics, and in problems of astronomy, the theory of relativity has proved to be the most fruitful and best verified by experience.

Physics faces the task of combining the theory of relativity with quantum theory, of further developing relativistic quantum dynamics. But physics has not established limits of applicability of the theory of relativity either in the large or in the small. This is an error of the reviewers.

The main place in the discussion of the theory of relativity, in particular also in the reproaches addressed to me, is occupied by the question, posed by the theory of relativity, of the relation between mass and energy.

Twenty years ago I expressed the undoubtedly erroneous supposition that, since matter and energy are equally indestructible, and since mass determines the entire store of energy of a given system, could it not also measure the quantity of matter? Such a rapprochement of matter and energy, far from Engels’ way of posing the question, recalls the ideas of the energetists. Since then I have repeatedly spoken of this error. It is also reflected, among other things, in my objections, far removed from Ostwald’s energetism, which I have always considered a false and harmful delusion. Now I have been reminded of my error. I acknowledge it and regret it.

But in the 1949 book there is no such identification of matter and the state of its motion. It is a question of the relation not of matter, but of the mass of any system, the mass that determines its inertia and weight, to the totality of all kinds of energy of that same system.

This is what the authors of the review, I. V. Kuznetsov and N. F. Ovchinnikov, charge me with. They point out that some, especially foreign, authors speak of the transformation of mass into energy and that they support these statements by reference to equivalence, and further: “if A. F. Ioffe himself in his book nowhere speaks of such a transformation of mass or even of substance into energy, then in his exposition the law … is transformed into an arithmetical rule that makes it possible to measure energy in ergs and in grams.” “It should be noted, however, that in giving a concrete characterization of the energetic aspect of nuclear processes A. F. Ioffe … quite correctly says that a definite amount of mass corresponds to a definite amount of energy.”

However, in some of the statements made by me they join even those physicists who speak of the transformation of substance into energy.

The authors of the review, like other philosophers, consider incorrect the assertion of the “equivalence” of mass and energy, which they immediately substitute by identity and set against it their interrelation as the correct expression of the relation between them.

Despite the extreme reluctance to understand the meaning of the dispute over equivalence or interrelation, I do not see its significance either for physics or for philosophy. However, since both in my book and in the critical remarks concerning it the question of mass and energy constantly figures, I consider it my duty to define before the reader my attitude to this problem.

With respect to that kind of matter which we call electromagnetic waves or photons, which do not possess rest mass and move with the speed of light, it is undoubtedly established that the total reserve of energy of any such system determines its gravitational and inertial mass.

With respect to matter which it is customary to call substance and which differs in its ability to move relative to the surrounding medium with a speed different from the speed of light and, in particular, with zero speed, such a universal connection of all mass with all energy is still only an assumption. Until experiment has established the conditions for the formation of an antiproton, there is as yet no direct proof that the energy of the proton as a whole corresponds to its mass.

However, it is difficult to think that this is not so. There are, on the contrary, grounds for asserting that not only a change in energy is connected with a change in mass, but that the entire reserve of energy is connected by the same relation with the entire mass of the system. This proposition I expressed in the book, as it seems to me, correctly by the statement that the mass of a body is the measure of all the kinds of energy contained in it. (This does not at all mean that mass is only a measure of the reserve of the body’s energy.)

If the mass of a body has changed, then its energy has also changed correspondingly, and the change in the body’s energy is equivalent to the change in its mass.

A proton, flying into a lithium nucleus with a comparatively small kinetic energy, transforms it into two rapidly separating helium nuclei. The “rest mass” of the new nuclei is less than the “rest mass” of the original ones by an amount corresponding to the increase in kinetic energy. But the total mass of all particles, measured with allowance for their speed, has, of course, not changed, because the total reserve of energy has not changed.

How should such phenomena be set forth? Using the quantity of mass as expressed by the theory of relativity, one should assert that in this process the mass of the whole system before and after the process was conserved, just as the total reserve of energy was conserved in the whole closed system.

But if we were always to use such a device, we would complicate the concept of kinetic energy. It is based on separating those forms of energy which are embraced by “rest mass” from the additional form of energy which we call kinetic. The singling out of kinetic energy leads to the assertion that a change in rest mass is “equivalent” to a change in kinetic energy.

By weighing we measure the mass of a body independently of its chemical nature and individual properties. Mass says nothing about particular forms of energy, but only about its total amount. Mass, determining the inertial and gravitational properties of a body, is qualitatively different from the energy of this body, which measures a definite kind of motion inherent in the body.

The term “equivalence” has become attached to the relation of two different forms of energy, for example thermal and kinetic. One may doubt its suitability for relating a quantity characterizing the total store of energy to one of its separate forms. However, the term “interrelation” seems still more unfortunate and even more ambiguous. Interrelation, for example, correctly characterizes the relation of the electric and magnetic fields. The mutual transition of the electric field into the magnetic and, conversely, of the magnetic into the electric in periodic processes creates an interrelation between them. But it is precisely against such an “interrelation” that the authors of the review are fighting.

In the question of the connection between mass and energy, as it is set forth in my book, and in the word “equivalence,” I see no philosophical errors. Of course, the unfortunate phrase “energy possesses mass” is unsuccessful. It is true that I do not always make clear in my exposition what mass is meant, even when I have in mind “rest mass.” It would have been quite pointless and, perhaps, naive to prove that the framework of the conservation laws does not limit our technical possibilities, despite the fact that they can be expressed as the impossibility of perpetual motion of the first and second kinds, the attainment of absolute zero, and so on. It is precisely mastery of the laws of nature that opens the way to their use and frees us from fruitless attempts to realize perpetual motion and other similar chimeras.

“People can discover laws, know them, master them, learn to apply them with full knowledge of the matter, use them in the interests of society, and thus subjugate them,” says Comrade Stalin.

From time to time there is still recalled the accusation of my incorrect attitude toward the law of conservation of energy. The history of this accusation is connected with the work of the Alikhanov brothers, who experimentally and convincingly refuted Shankland’s experiments and the Bohr and Slater theory underlying them concerning the inapplicability of the laws of conservation of energy to quantum processes, or that the law is valid only statistically. A number of authors considered the law of conservation of energy, for example, inapplicable to nuclear processes in stars and even went so far as to create the energy of stars out of nothing.

Both then and now I hold that the laws of nature, reflecting its objective properties, are known as a generalization of experience, and that the concrete content of the law of conservation of energy is also given by experience. From the apparent violation of the law of conservation of energy in beta decay there emerged the neutrino. It was impossible in advance to exclude the possibility of new, as yet unstudied forms of energy in quantum processes, however improbable this seemed.

The experiments of the Alikhanovs proved the absence of such unknown forms of energy in the formation of two photons and rejected any revision of the law of conservation of energy. It is good that we were able to oppose to the theory of Bohr and Slater the assertion: “this is not so, it contradicts the facts,” instead of “this cannot be, proceeding from the indestructibility of motion; it is not worth proving,” as some philosophers suggested I should do. The question would

ON THE QUESTION OF THE PHILOSOPHICAL ERRORS OF MY BOOK

...hung for a long time in the air, whereas the Alikhanovs’ experiment eliminated it once and for all.

I understand the significance and universal validity of the proposition on the conservation and transformation of energy in the same way as my critics. In this there were, and are, no disagreements. But the experiment nevertheless ought to have been carried out. In this I am now convinced.

I have more serious shortcomings in my exposition of quantum theory.

Besides the unfortunate classical analogies to the quantum process of penetration of particles through an energy barrier, my book contains no consistent exposition of the distinctive character of a microparticle by means of its wave function, and the meaning of the wave function is not disclosed.

I wrote my book, however, in 1947, when the understanding of the wave function which Soviet physicists Fok, Blokhintsev, and Aleksandrov have advanced in recent years did not yet exist. At that time Soviet physicists cited the same examples of the distinctive character of quantum laws as foreign authors, though, of course, drawing from them different, materialist conclusions.

That is what I did as well: in expounding the uncertainty relation as a limit of measurability (and not of applicability, as should have been done) of the classical characteristics of an object (coordinates, momentum), I nevertheless emphasized that this limit characterizes new properties of the micro-object, properties essentially different from those of a classical little ball, and that the uncertainty relation does not in any degree limit the knowability of the external world. The book explains in detail that the wave nature of microparticles renders meaningless the very question of the exact coordinate of a wave moving with a given velocity in space. It is impossible to say at what point a wave is located, not because we cannot know this, but because a wave cannot be located at a point, because there can be no answer to a meaningless question; and as an illustration I give the absurd question about the mechanism of the flight of a snake which, as Gorky observed, cannot fly.

The objective content of the uncertainty relation is also illustrated in the book, for example, by the width of spectral lines, independent of our experimental skill or of the observer’s influence, which according to the uncertainty relation is connected with the lifetime of the quantum states of the electron in the atom. The meaning of the uncertainty relation can be explained better than this was done in the book. But I consider the accusation that I expounded the “principle of uncertainty” in the spirit of agnosticism to be unfounded. Moreover, my whole book is devoted to a vivid demonstration of the boundless knowability of the world in its continuously unfolding diversity.

I strove to show—and, I think, convincingly showed in my book—that the combination in a micro-object of corpuscular and wave properties follows with iron necessity from the experimental facts presented, that it expresses the objective distinctive character of the microworld. If one proceeds from these facts, then the quantum laws of the microworld are just as indubitable and natural as the laws of classical physics of the nineteenth century, which are the limiting form of twentieth-century physics.

All my fifty years’ experience, my reflections on the problems that arose during this time, my personal attempts to resolve them, and the conclusions obtained as a result of research—all this invariably convinced me of the absolute correctness of the propositions of dialectical materialism, as Engels and Lenin formulated them and as Comrade Stalin creatively developed them.

I saw that physics proceeds along the paths foreseen by V. I. Lenin, that every new discovery fundamentally refutes, rather than confirms, the idealist conceptions of agnosticism, of the denial of causality, of phenomena outside time and space.

Comparing such idealistic conclusions with the actual content of physical laws, I clearly saw the falsity of these conclusions; I saw that the spread of idealism is facilitated by the unusual character and the lack of clarity in the new physics.

It was this obstacle that I wanted to remove with my book, by showing broad circles of readers that behind the unusual concepts there is not the slightest ground for idealism. I think I succeeded in proving this. But the authors of the review showed that there are phrases which, if desired, may be understood “in the spirit of agnosticism.” Thus, apparently, ambiguous expressions should not be present in a popular book.

Having set forth the paths of development of physics over the last 50 years, I tried to illustrate, on this material, how comprehensively the propositions of dialectical materialism are confirmed. In the last chapter, in the form of a summary, the data from the history of twentieth-century physics are compared with the corresponding propositions of dialectical materialism.

In the opinion of Comrades Kuznetsov and Ovchinnikov, this was done unsuccessfully. It is true, in any case, that the task of correctly philosophically interpreting quantum phenomena is not solved in my book.

I myself see now the shortcomings in the exposition of quantum mechanics in my book, which I did not notice then. Such a shift can also be observed along the whole physical front. In this I see the result of our Party’s persistent struggle for the ideological growth of scientific cadres, for their mastery and development of the philosophy of dialectical materialism.

The progress achieved over the last five years can be assessed if one compares the exposition of quantum phenomena in my book (quite typical for 1947–1948) with the later formulations of Fok, Blokhintsev, and Aleksandrov.

Although many errors have now been revealed and removed from physics textbooks, we still do not have, as it seems to me, an impeccable formulation of quantum laws. I am satisfied neither by Blokhintsev’s ensemble nor by Fok’s understanding of the wave function as a complete description of the properties of a micro-object. After all, there do exist real phenomena of the motion of individual electrons or photons, which do not fit into any of the formulas. Still worse, the theory of the quantum field proposed by Blokhintsev and Frenkel—it degenerates into Shredinger’s idealistic idea about the absence of long-existing objects of observation. I do not consider hopeless the attempts by Bohm, Weizel, and others to develop a theory with unambiguous causality.

But all this in no way justifies a number of shortcomings in the exposition of quantum phenomena and the uncertainty principle noted by Comrades Kuznetsov and Ovchinnikov. Of course, in 1954 one can and should demand a more consistent description of the distinctive character of microphysics, and, of course, neither then nor now can one speak of a synthesis of concepts (this is one of my real philosophical errors; I obviously did not imagine the conclusions that could be drawn from this phrase).

In some places I am ascribed views that I did not express; for example, that “in quantum mechanics the conception of classical trajectory motion along definite orbits is preserved.” It is enough to open pp. 200–201, where this question is discussed, to see: “the conception of the motion of an electron along a definite closed orbit inside the atom is incompatible with the uncertainty principle and with the wave properties of motion,” and further, an illustration of this proposition by the example of the hydrogen atom and a statistical interpretation of the wave function.

The statement that there are no electromagnetic waves in my book is quite correct and, I would add, there is no physics of oscillations and waves in general. I have never dealt with these branches of physics and could hardly have said anything about them—

ON THE QUESTION OF THE PHILOSOPHICAL ERRORS OF MY BOOK

something of their own, which is not in other books. In the preface, noting the narrow selection of topics considered in the book, I appealed to specialists in optics with a proposal that they set forth the basic ideas in their field. Unfortunately, this appeal was not heard, and there are still no analogous books in other areas of physics, although the authors of the review acknowledge their usefulness. Evidently, a one-sided criticism of my book by philosophers has not evoked a desire to continue the work that had been begun.

But the relation between the electromagnetic wave and the photon has long and deeply interested me. In 1907 I indicated how the photoelectric effect with alkali metals could test the idea of photons. Over the course of four years I conducted these experiments, but in the publication they were passed over in silence by Millikan. In 1911 I constructed a theory of radiant energy as a statistics of photons and, in particular, came to the conclusion that, in order to obtain the correct form of the formula for black radiation, it was necessary to change the statistics in the direction proposed by Bose 12 years later.

Yu. A. Krutkov developed and proved this idea of mine somewhat later. In 1913 my article on the theory of radiant energy appeared in Khvolson’s physics course.

In 1912–1913 I carried out experiments on the elementary photoelectric effect with the aim of clarifying the possibility of the accumulation of the energy of a photon from the electromagnetic field. In 1924 there appeared the experiments with single X-ray photons conducted by me jointly with N. I. Dobronravov.

In my book I repeatedly dwell on these experiments, which, however, did not provide me with a solution to the question of how the energy of a spherical electromagnetic wave is wholly absorbed in the small volume where the photon was absorbed.

It cannot be said, therefore, that in my scientific life and in my book, which reflects it, I passed by the electromagnetic field. Trying to construct a photon theory of light by analogy with the kinetic theory of gases, I came to the conclusion that, along with the analogies, there is an essential difference between particles of matter and photons, a difference that does not allow me, as the authors of the article propose, to classify the photon (and together with it the phonon and the exciton) among the elementary particles along with the electron and the proton.

Here I differ from the authors of the article, but I think that my point of view is better substantiated.

The authors of the review ask: what, then, is wrong with the idea of the wave nature of matter? This idea, in the form against which I objected, A. A. Zhdanov called devilry. And I have had occasion to encounter it, and still do.

Nor do I think that the reader can derive from my book the impression of the “completeness” of physical science, since the book sets out its dynamics.

In the knowledge of nature there are generalizations which, within the limits of all accumulated experience, remain firm achievements of science. I constantly emphasize the relative character of the knowledge of the laws of nature and the limits of the validity of our present-day knowledge, but, evidently, the point is that I draw the boundaries not where the authors of the article see them.

They believe that the boundary of applicability of the theory of relativity is the macroworld, but not too large; I do not think so. The authors, apparently, want to see the boundaries of quantum theory not at its transition to the relativistic one, but within the limits of atomic phenomena. For this, in my opinion, there is no basis.

On the other hand, the authors see no enigma in the electromagnetic field of a single impulse, and do not see an essential difference between the electron or the proton, on the one hand, and the photon and the phonon, on the other, despite the similarity of many properties.

Probably also in our understanding of the role of charge in the structure of matter, of the relations between the electron and mesons, of the spontaneous decay of the neutron—we shall go on diverging.

But this, too, shows that there can be no talk of physics being complete, even with respect to already known phenomena of nature. And what can be said about nuclear forces, about the neutrino, the neutretto, and other still little-known objects?

A large section of the critical article is devoted to the statistical method. I agree with the reviewers that one ought not to have substantiated the inevitability of statistical methods in physics, but to have shown their adequacy to the problems under study.

But the fact that they object to the statistical interpretation of the second law of thermodynamics, as it is set forth in the book, shows that they have not understood the difference between the statistical method and classical thermodynamics. This is how they, for example, present it: “Thus, in nature there exists a certain most probable state of equilibrium, toward which it inevitably tends. In this state all processes cease.” This is an exposition of the second law of formal thermodynamics, and an incorrect one at that. With respect to the statistical understanding of the second law, everything here is wrong: first, it concerns a closed system, not nature in general; second, the system does not remain in the most probable state, but in constant fluctuations differing from it; third, in this state processes do not cease, but continue uninterruptedly, and in complex systems from time to time develop into arbitrarily large fluctuations, which are again followed by a long period of approach to more probable states. Such is the content of Boltzmann’s doctrine, which I tried to explain in my book without vulgarization. It deserves a more serious analysis than that made by my critics. Then, I think, they would understand why I call the propositions of thermodynamics formal. Then they would notice that the statistical understanding of the second law excludes the idea of the heat death of the world and fundamentally undermines religious notions of the intervention of otherworldly forces in the destinies of the world.

A statistical analysis of molecular processes gives a clear understanding of the laws of thermodynamics in this domain. Whether there are grounds, in the field of biology or in world processes, for posing the question differently will be shown by the future.

Comrades Kuznetsov and Ovchinnikov reject my assertion that the agnosticism of Du Bois-Reymond and the energetics of Ostwald, his denial of the reality of atoms, were accepted at the end of the nineteenth century by the majority of physicists not connected with the kinetic theory of gases or with chemistry. That is how the situation was described to me by contemporaries of that epoch: Langevin, Röntgen, and Lorentz. Few physicists of that time came forward in print with an exposition of their philosophical views. And in the oral conversations, apparently, skeptical views were expressed by physicists then young. My information was borrowed only from the words of the physicists named above and of some others. It is possible that they, and along with them I, were mistaken in estimating how widespread such attitudes were.

In refutation of my opinion, the authors of the review cite, however, representatives of chemistry, whose attitude is not disputed among us, and in particular the leading Russian chemists: Butlerov, Markovnikov, Mendeleev. I could add, among foreign scientists, representatives of the kinetic theory of gases—Boltzmann, Knudsen, and a number of others. But is not the fact—the suicide of Boltzmann, whom Ostwald’s philosophy tried to isolate from the main paths of the development of physics—the very beginning of the triumph of his ideas and the beginning of the collapse of all Ostwald’s predictions?

The absurdity of Ostwald’s energetics was exposed by physicists and philosophers already in the first decade of our century, especially convincingly by V. I. Lenin. Now, apparently, someone is trying to galvanize ener-

ON THE QUESTION OF THE PHILOSOPHICAL ERRORS IN MY BOOK

...energetism, making use of the connection between energy and mass. Since energetism is an idealist current, its erroneousness must be exposed. But along with the struggle against historically obsolete currents of the past that have been revived again, greater attention should have been paid to the exposure of the militant idealism of contemporary physicists, to the struggle against the campaign undertaken by our present-day foreign ideological enemies against materialism on the basis of quantum theory.

As the contradictions between the camp of peace and democracy, on the one hand, and aggression and reaction, on the other, become more acute, the idealist statements of many foreign physicists become ever more definite and hostile. Instead of isolated, often merely incidental, idealist remarks, the deliberate propaganda of obscurantist idealism and the striving to overthrow the foundations of materialism are heard more and more loudly.

When I wrote the book, I did not know Heisenberg’s 1945 speech on Planck, in which he resolutely denies the concept of reality and the very possibility of phenomena taking place in time and space. The journal Dialectica had not yet appeared, in which Bohr’s principle of complementarity revealed itself in all its reactionary essence. Einstein’s Machist views had not yet received the development they did in the articles of his apologist Ph. Frank. Although the idealist positions of all these authors, Jordan’s racism, and the idealist views of Dirac and Schrödinger had long since become apparent, they had never before assumed such a militant character as in Schrödinger’s recent booklet Science and Humanism. Physics of Our Time, where he declares the “task of his life” to be: 1) the struggle against materialism and 2) the conviction of “Western” readers that the sole aim of science is to answer the question of who we are and why we have appeared in the world. Here the author’s “Western” ideas are set, with all sharpness and polemical fervor, against the materialist worldview and against the striving that science should benefit humanity (whence it is not far to the justification of the use of the atomic bomb).

It is enough, however, to set against Schrödinger’s nebulous phrases the actual content of the laws of physics, even if presented as imperfectly as it is in my book, in order to be convinced of the inconsistency of the entire construction. The unequivocal causality of the wave function replaces the statistical causality of the corpuscular picture as one of the forms of the more general principle of causality. The concrete combination of the corpuscular and wave properties of a microparticle, given by experiment, makes it just as real an object of the external world as the macro-objects of classical physics. Matter has not disappeared in quantum physics; rather, the limits and forms in which we knew it before have expanded.

All similar attempts to deny matter, every time new aspects of it are revealed, were exposed and shattered by V. I. Lenin. Schrödinger’s argumentation is merely a rehashing of the same motifs in a new key.

Nevertheless, at every turn in physics there again appear the routed remnants of leaders going into battle against matter with the same unsuitable weapon. A murky fog is needed, under cover of which already defeated idealism spreads.

The fog is intensified still more when it is combined with the scientific authority of a priest of science who considers himself entitled to prophesy, without offering proofs, as Schrödinger does in his pamphlet, counting on the audience’s trust.

A resolute struggle against idealist theories is necessary, in whatever form they may appear. There is no such struggle in my book. In the 1930s I did not foresee the development of the idealist remarks of the authors of the theory of relativity and quantum theory into a system of idealist conceptions. I underestimated the hostility of these conceptions even when my book was being written. This is my error.

Resolutely condemning and shattering the philosophical position of Einstein, Bohr, Heisenberg, and Schrödinger, one should not, however—as is unfortunately done by some philosophers—reject those of their theories that have been tested and confirmed by experience.

Foreign idealists try to convince us that the denial of reality, agnosticism, and the denial of causality are inevitable conclusions from contemporary physical theories; and among us there are philosophers who, having fallen for this bait, reject such dangerous theories and thus involuntarily pour water on their mill.

In fact, quite the opposite is true: the growing knowledge of the phenomena of nature, expressed in our time both in the theory of relativity and in quantum theory, ever more and ever more unquestionably confirms the correctness of dialectical materialism. This was brilliantly shown by V. I. Lenin with respect to the theories of the beginning of the century; it remains true for theories of the present, tested by new and extensive experience. They must be correctly understood from the standpoint of dialectical materialism, and not rejected because abroad they are used for idealist arguments.

My book lacks a sharp struggle against the idealism of Western physicists. But I think that all unprejudiced readers have been convinced that modern physics, in the entire course of its development, confirms the philosophical propositions of dialectical materialism; that it provides not the slightest basis for idealist conceptions. Such was the task of the book. My critics have shown that it can be accomplished better.