Every particle exhibits the properties of both particles and waves.

But dialectical materialism insists on the approximate, relative character of every scientific theory of the structure of matter and its properties; it insists on the absence of absolute boundaries in nature, on the transformation of moving matter from one state into another, that from our point of view is apparently irreconcilable with it, and so forth. However bizarre from the standpoint of “common sense” the transformation of imponderable ether into ponderable matter and vice versa may appear, however “strange” may seem the absence of any other kind of mass in the electron save electromagnetic mass, however extraordinary may be the fact that the mechanical laws of motion are confined only to a single sphere of natural phenomena and are subordinated to the more profound laws of electromagnetic phenomena, and so forth – all  this is but another corroboration of dialectical materialism. It is mainly because the physicists did not know dialectics that the new physics strayed into idealism. They combated metaphysical (in Engels’ and not the positivist, i.e., Humean, sense of the word) materialism and its one-sided “mechanism”, and in so doing threw out the baby with the bath-water. Denying the immutability of the elements and of the properties of matter known hitherto, they ended by denying matter, i.e., the objective reality of the physical world. Denying the absolute character of some of the most important and basic laws, they ended by denying all objective law in nature and by declaring that a law of nature is a mere convention, “a limitation of expectation”, “a logical necessity”, and so forth. Insisting on the approximate and relative character of our knowledge, they ended by denying the object independent of the mind, reflected approximately-correctly and relatively-truthfully by the mind. And so on, and so forth, without end.

The opinions expressed by Bogdanov in 1899 regarding “the immutable essence of things”, the opinions of Valentinov and Yushkevich regarding “substance”, and so forth – are similar fruits of ignorance of dialectics. From Engels’ point of view, the only immutability is the reflection by the human mind (when there is a human mind) of an external world existing and developing independently of the mind. No other “immutability”, no other “essence”, no other “absolute substance”, in the sense in which these concepts were depicted by the empty professorial philosophy, exist for Marx and Engels. The “essence” of things, or “substance”, is also relative; it expresses only the degree of profundity of man’s knowledge of objects; and while yesterday the profundity of this knowledge did not go beyond the atom, and today does not go beyond the electron and ether, dialectical materialism insists on the temporary, relative, approximate character of all these milestones in the knowledge of nature gained by the progressing science of man. The electron is as inexhaustible as the atom, nature is infinite, but it infinitely exists. And it is this sole categorical, this sole unconditional recognition of nature’s existence outside the mind and perception of man that distinguishes dialectical materialism from relativist agnosticism and idealism.

…the new physics wavers unconsciously and instinctively between dialectical materialism, which remains unknown to the bourgeois scientists, and “phenomenalism”, with its inevitable subjectivist (and, subsequently, directly fideist) deductions.

…it is nevertheless beyond question that mechanics was a copy of real motions of moderate velocity, while the new physics is a copy of real motions of enormous velocity. The recognition of theory as a copy, as an approximate copy of objective reality, is materialism. When Rey says that among modern physicists there “is a reaction against the conceptualist [Machist] and energeticist school”, and when he includes the physicists of the electron theory among the representatives of this reaction, we could desire no better corroboration of the fact that the struggle is essentially between the materialist and the idealist tendencies. But we must not forget that, apart from the general prejudices against materialism common to all educated philistines, the most outstanding theoreticians are handicapped by a complete ignorance of dialectics.

V.I.Lenin, Materialism and Empirio-Criticism: Critical Comments on a Reactionary Philosophy, 1908, Progress Publishers, Moscow, 1975, pp. 240-246

Text, with minor errors, at:
https://www.marxists.org/archive/lenin/works/1908/mec/five2.htm#v14pp72h-258