Boltzmann, Monocycles and Mechanical Explanation

Abstract

For more than two hundred years — from Isaac Newton in the seventeenth century to Ludwig Boltzmann at the close of the nineteenth — physical theory had a fixed, clear goal. Christiaan Huygens expressed it in his Treatise on Light in 1690, when he referred to “the true Philosophy, in which one conceives the causes of all natural effects in terms of mechanical motions.”¹ Huygens was convinced that either one sought for mechanical explanations or else one had to “renounce all hopes of ever comprehending anything in Physics.” Newton’s Principia became the great model that scientific theory was to follow, and Newton was very definite in his views on this subject. “The whole burden of philosophy,” he wrote, “seems to consist in this — from the phenomena of motions to investigate the forces of nature, and then from these forces to demonstrate the other phenomena.” To this end he had developed the rational mechanics of the first two Books of the Principia, and his ‘explication of the System of the World’ in the third Book was merely ‘an example’ of his method — a superb example, but an example nevertheless. Newton expressed the wish that “we could derive the rest of the phenomena of Nature by the same kind of reasoning from mechanical principles.” ² This wish described the program of generations of New-ton’s successors who tried to do for the other forces of nature what he had done for gravitation.