# Ludwig Boltzmann: The Man Who Trusted Atoms

# Ludwig Boltzmann: The Man Who Trusted Atoms

## Synopsis

## Excerpt

Our now standard picture of matter, as presented by the physics of today, tells us that ordinary macroscopic materials are made up of *atoms.* Although the essentials of this picture go back to early Greek times, its general acceptance is remarkably recent. From about the middle of the nineteenth century, a gradually increasing number of physicists were indeed coming to accept the reality of atoms, but there were still a great many who regarded this “atomic hypothesis” as merely a convenient fiction which did not reflect any genuine reality at a submicroscopic level.

This “hypothesis” did, nevertheless, enable (non-obvious) macroscopic qualities of substances to be deduced. in principle, knowing the laws governing the individual atoms provides a means for deducing the overall properties of materials. Yet, there is no remotely practical procedure for calculating the behaviour of a macroscopic body from a detailed calculation of the motions of all of its constituent atoms. the number of atoms making up any ordinary macroscopic system is far too enormous. a cubic centimetre of air, for example, contains some 10 atoms. Thus, to deduce how a macroscopic material must behave, according to our standard picture, it is necessary to employ *statistical *arguments. the laws governing macroscopic behaviour are obtained from the forming of appropriate statistical averages of physical parameters of individual atoms. Such procedures were beginning to be worked out by a number of physicists in the second half of the nineteenth century, but the outstanding figure among these was *Ludwig Boltzmann.*

Boltzmann stands as a link between two other great theoretical physicists: James Clerk Maxwell in the nineteenth century and Albert Einstein in the twentieth. Maxwell, who is best known for his discovery of the laws governing electric and magnetic fields and light, first found the formula for the probability distribution of velocities of particles in a gas in equilibrium, but it was Boltzmann who derived the equation governing the *dynamical evolution* of the probability distribution, according to which the state of a gas, not necessarily in equilibrium, will actually change. Boltzmann’s ideas were central to Max Planck’s later analysis of black body radiation at the turn of the century, in which he introduced the *quantum of action,* thereby firing the opening shot of the quantum revolution. in 1905, Einstein not only picked up on this idea and developed it further (in effect showing that the “atomic hypothesis” applied even to light itself!) but was also influenced by Boltzmann’s concepts in two of his other famous papers of 1905, one in . . .