14 SEPTEMBER 2006
His death was a shock to science, as Boltzmann was one of the giants of physics. His possessed a 20th century mind surrounded by 19th century thought, and he struggled to drag physics into its future against the inertia of intellectual intransigence. In the process he explained the science of heat, helped establish the existence of atoms and tried to understand the arrow of time.
Born in Austria in 1844, Boltzmann became a prominent figure in European
physics by the 1870s. Building on foundations laid by James Clerk Maxwell,
the 19th century's greatest theoretical 
physicist,
Boltzmann developed the use of probability theory to expand physics beyond
the confines established by Newton's laws of motion.
Maxwell knew that it wasn't feasible to apply Newton's laws directly to compute the paths and path-changing collisions of gazillions of molecules bouncing around in a gas. So Maxwell pioneered the use of statistics to describe molecules, using probabilities for how they moved to determine a gas's properties. Temperature, for example, could be calculated on the basis of average molecular velocities.
Boltzmann expanded Maxwell's approach, using statistics to describe molecules not only individually, but to quantify all the different ways that molecules (or atoms) might arrange themselves in a gas or other substances. What ultimately emerged from Boltzmann's work was the branch of physics known as statistical mechanics, widely used today to describe matter in all sorts of circumstances. Statistical mechanics, Boltzmann showed, provided the foundation for understanding the laws governing the flow of heat.
Since Boltzmann's math was based on the idea that matter consisted of molecules in motion -- molecules being units made from atoms -- its success implied that atoms really existed. Yet even though many physicists and chemists believed in atoms, some remained skeptical, suggesting that atoms were merely convenient fictions that simply allowed chemists to predict the outcome of chemical reactions.
Boltzmann argued vociferously with the anti-atomists, particularly the physicist Ernst Mach and the chemist Wilhelm Ostwald. Ostwald insisted that a purely energy-based theory could explain all the experimental results. At one point in 1890, Boltzmann retorted that energy could also consist of atoms of a sort -- a prophetic anticipation of the discovery of quantum physics by Max Planck a decade later, which showed that energy does package itself in indivisible units.
Despite
Boltzmann's arguments, the atom controversy remained alive until after
Boltzmann died. Definitive evidence for atoms arrived in 1908 from experiments
by Jean Perrin in France, based on a theoretical analysis by Einstein
in 1905. Einstein's paper was probably unknown to Boltzmann when he hanged
himself near Trieste on Sept. 6, 1906.
Sometimes it is said that Boltzmann chose suicide in despair over resistance to his science, but there's no real evidence for that. He had long suffered from mood swings and had other serious health problems, including asthma, headaches and deteriorating eyesight.
"His suicide seems to have been due to factors in his personal life (depression and decline of health) rather than to any academic matters," write Indian physicists S. Rajasekar and N. Athavan in a recent paper available online.
Still, Boltzmann's lifelong struggles against intellectual inertia taught a lesson that he articulated in a major address delivered in St. Louis in 1904. His message involved the need for skepticism of philosophies trying to deduce features of nature divorced from experimental facts.
Theories come and go, but facts persist forever, Boltzmann declared. Established facts may need to be arranged within a new theoretical framework, but they must be accommodated by whatever theory comes along. And however well any given theory connects the facts, there is always a chance that a better theory will someday appear.
"It will always be possible that a new theory will arise which has not yet been tested by experiment and which will represent a much larger field of phenomena," Boltzmann observed.
But that doesn't mean that theorizing must, or should, be constrained by the facts of the moment. In his efforts to understand why time always flows forward (while Newton's laws work the same toward future and past), Boltzmann applied statistical reasoning to the universe as a whole.
The future happens as improbable arrangements of matter become more probable. And the most probable arrangement of all is utter mixture, with no distinction between time going forward or backward. But despite eons of time passing by, the universe isn't like that. It contains rich structures of solar systems and living organisms.
Boltzmann explained that in a universe sufficiently large, the laws of probability allowed some regions to exist that were not yet completely mixed -- spots could be found with stars and structures where time seemed to flow only forward.
"Were thinking beings at such a spot, their impressions of time would be the same as ours," Boltzmann said, "although the course of events in the universe as a whole would not be one-sided."
His ideas about time remain controversial even today. But they illustrate the value of science that goes beyond established facts to seek grander explanations of existence.
"The above-developed theory does indeed go boldly beyond our experience," Boltzmann said of his probabilistic view of time. "But it has the merit which every such theory should have -- of showing us the facts of experience in an entirely new light and of inspiring us to new thought and reflection."
E-mail: tsiegfried@nasw.org
