Les Hearn marks the centenary of Albert Einstein's confirmation of the existence of atoms
"If, in some cataclysm, all scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis ... that all things are made of atoms".
Thus the physicist Richard Feynman described the importance of a fact that we all learn at school. It is hard to believe that as recently as 100 years ago this was just a hypothesis, and one that several eminent scientists refused to accept. It was a useful hypothesis and enabled scientists to model the interaction of matter and heat very accurately. But no-one had ever seen an atom and people naturally like to be able to see things.
And then along came Einstein. In the year 1905, he published five earth-shattering scientific papers, one of them literally so in that it laid the ground for the atom bomb. One of the others, however, showed how the existence of atoms themselves could be proved.
About 80 years before Einstein's "discovery", the botanist Robert Brown was trying to look at pollen grains in water under a microscope. To his surprise, they would not stay still but jerked around randomly in an incessant dance. Changing the temperature or light level had no effect. Furthermore, this "Brownian" motion happened with any small particles, not just living ones, showing that it was a physical property.
It took Einstein's genius to see that, if atoms existed, they would be in thermal equilibrium with any other particles, such as pollen grains. They would bump into each other and with the pollen grains. By the laws of chance, the particles would be knocked this way and that. But, while atoms were too small and fast-moving to be seen, the pollen could be seen and it would be possible to measure its size and rate of diffusion. Einstein was able to predict how these two factors would be connected, given the existence of atoms, and soon afterwards French physicist Jean Perrin was able to confirm his prediction.
The sceptics finally had to accept the reality of atoms.
Incidentally, one of these sceptics was Ernst Mach, a physicist and philosopher (Mach numbers are named after him). In 1905, following the defeat of the first Russian revolution, Lenin found that he had enough time on his hands to write a critique of Mach's idealist philosophy in the book Materialism and Empirio-criticism. Another physicist with a philosophic bent was Wilhelm Ostwald, who theorised that, while atoms were a useful shorthand for understanding physical phenomena, all matter was energy. He too was forced to accept the existence of atoms.
Ironically, Einstein also showed in the same year that matter and energy could be interconverted, according to the relation E = mc2.
Ocean books have recently published a book about Einstein's socialist views, as part of their series on "Rebel Lives". Well worth acquiring.