From “In Search of Schrödinger’s Cat: Quantum Physics and Reality
This excerpt is about 1905, and the groundbreaking papers Einstein published in that year.
This paper was just one of three published by Einstein in the same volume of the Annalen der Physik in 1905, any one of which would have assured him of a place in the annals of science. One of the papers introduced the special theory of relativity and is largely outside the scope of the present book; another concerned the interaction of light with electrons and was later recognized as the first scientific work dealing with what we now call quantum mechanics — it was for this work that Einstein received the Nobel Prize in 1921. The third paper was a deceptively simple explanation of a puzzle that had baffled scientists since 1827 — an explanation that established, as far as any theoretical paper ever could, the reality of atoms.
Einstein later said that his major aim at that time was “to find facts which would guarantee as much as possible the existence of atoms of finite size,” an aim that perhaps indicates the importance of the work at the beginning of the present century. At the time these papers were published, Einstein was working as a patent examiner in Berne — his unconventional approach to physics had not made him an obvious candidate for an academic post when he completed his formal education, and the patent office job suited him. His logical mind proved well able to sort out the wheat of new inventions from the chaff, and his skill at the job left him plenty of free time in which to think about physics, even during office hours. Some of his thoughts concerned the discoveries made by the British botanist Thomas Brown almost eighty years before. Brown noticed that when a pollen grain floating in a drop of water is examined using a microscope it is seen to bounce around in an irregular fashion, moving in a random pattern that is now called Brownian motion. Einstein showed that this motion, although random, obeys a definite statistical law, and that the pattern of behavior is exactly what should be expected if the pollen grain is being repeatedly “kicked” by unseen, submicroscopic particles that move in accordance with the statistics used by Boltzmann and Maxwell to desscribe the way atoms move in a gas or liquid. It looks so obvious today that it is hard to credit what a breakthrough this paper made. You or I, used to the idea of atoms, can see at once that if pollen grains are being jostled by unseen collisions then it must be moving atoms that push them around. But before Einstein made the point, respected scientists could still find room to doubt the reality of atoms; after his paper appeared, there was no longer room to doubt. Easy when explained, like the fall of an apple from a tree, but if it was so obvious why had it not been appreciated in the previous eight decades?
It’s ironic that this scientific paper should have been published in German (in the journal Annalen der Physik), because it was the opposition of leading German-speaking scientists such as Ernst Mach and Wilhelm Ostwald that seems to have convinced [Ludwig] Boltzmann that his was a lone voice crying in the wildnerness. In fact, by the beginning of the 20th century there was a great deal of evidence for the reality of atoms, even if, strictly speaking, that evidence could only be described as circumstantial.
