smrize logo

Want to extract relevant stories from a book? - Drop us a line at

Book Summary: Elemental

Author: Tim James

Substory: Einstein And Water Atoms

Albert Einstein was a legend in his own lifetime. What’s more impressive is that he deserved the reputation. Publishing over three hundred scientific papers and essentially inventing the landscape of modern physics, Einstein was the epitome of genius.

It would be foolish to summarize his many achievements in a few paragraphs, so we’ll focus on the one most relevant to chemistry: a paper he published on July 18, 1905, in which he made the atomic hypothesis testable rather than speculative.

While working at the Swiss patent office, Einstein stumbled across some research from 1827 by the Scottish botanist Robert Brown. Brown had noticed that grains of pollen floating on water appeared to jiggle in random patterns. Originally, he had assumed the grains were alive but found the same thing happened with sand or dust. The phenomenon was known as Brownian motion and, although unexplained, it was nothing more than a curiosity.

Einstein decided to model the pollen’s trajectory through the water and found it could only be explained as the result of bombardment from water particles. To accurately describe how the pollen moved, you had to factor in the friction of pollen against water, which meant you had to accept the existence of “water atoms.”

Despite the persistent rumors that he failed math in school, Albert Einstein was a mathematician par excellence and drew up an equation that related water temperature to the pollen grain’s likely movement. By introducing an equation with a measurable outcome, Einstein changed the game completely. An idea can be debated but a number cannot, so if you can predict a specific value from your hypothesis you have something to search for directly.

He finished his paper with the phrase, “It is to be hoped that some enquirer may succeed shortly in solving the problem suggested here.” As was usually the case with Einstein, his equation was soon tested and confirmed. The zigzagging wasn’t random at all, but the result of minor fluctuations in water movement on either side of the grain. Pollen looked like it was undergoing constant collisions because it genuinely was.

In finding this, Einstein did for the atomic hypothesis what Lavoisier did for the elemental one: he provided indisputable, quantitative evidence. You couldn’t sensibly discuss elements without atoms anymore, or vice versa. There was no argument to be had. Atoms were real.