In his 1902 book Science and Hypothesis, the French mathematician and physicist Henri Poincaré surveyed the landscape of modern physics and found three fundamental conundrums bedeviling his field: the chaotic zigzagging of small particles suspended in liquid, known as Brownian motion; the curious fact that metals emit electrons when exposed to ultraviolet light, known as the photoelectric effect; and science’s failure to detect the ether, the invisible medium through which light waves were thought to propagate. In 1904 a 25-year-old Bern patent clerk named Albert Einstein read Poincaré’s book. Nothing the young physicist had done with his life until that point foreshadowed the cerebral explosion he was about to unleash. A year later, he had solved all three of Poincaré’s problems.
“A storm broke loose in my mind,” Einstein would later say of 1905, the annus mirabilis, which John S. Rigden calls “the most productive six months any scientist ever enjoyed.” Between March and September, he published five seminal papers, each of which transformed physics. Three were Nobel Prize material; another, his thesis dissertation, remains one of the most cited scientific papers ever; and the fifth, a three-page afterthought, derived the only mathematical equation you’re likely to find on a pair of boxer shorts, E = mc2.
Rigden’s short book Einstein 1905 is a tour through each of those landmark papers, beginning with the only one that Einstein was willing to call “revolutionary.” That first paper, which would earn him the Nobel Prize sixteen years later, was titled “On a Heuristic Point of View About the Creation and Conversion of Light.” It could just as easily have been called “Why Everything You Think You Know About Light Is Wrong.”
In 1905 most scientists were certain that light traveled in waves, just like sound. Though it troubled few others, Einstein was deeply perturbed by the notion that energy could flow in continuous waves whereas matter was made up of discrete particles. To paraphrase Bertrand Russell, why should one aspect of the universe be molasses when the other part is sand? When Einstein tried to imagine a universe in which everything, including light, was made up of particles, he realized the simple conceptual shift could explain a lot, including the mysterious photoelectric effect. This was typical of how Einstein thought, argues Rigden. He saw fundamental contradictions in the generalizations that others had made before him and then followed the trail of logic to unexpected conclusions. In some cases it took years before his ideas could be experimentally verified. His theory of light wasn’t widely accepted for two decades.
The second paper of the year, completed in April, is the least well remembered, even though its many practical applications have made it one of Einstein’s most cited works. In that paper, Einstein suggested a way of calculating the size of molecules in a liquid based on measurements of how the liquid behaves. The paper relied on more mathematical brute force and was less graceful than the other four of the year, but it was important nonetheless. Because it showed how to measure the size of otherwise unobservable atoms, it helped nail the coffin shut on the few lingering skeptics, like Ernst Mach, who still did not buy into the atomic theory of matter.
Even more damning for those atomic skeptics was Einstein’s May paper on Brownian motion, which explained the unpredictable dance of pollen grains in water. The reason for the pollen’s erratic behavior, Einstein demonstrated, is that it is being constantly bombarded by water molecules. Most of the time, that bombardment occurs equally from all angles, so the net effect on a grain of pollen is zero. But sometimes, statistical fluctuations conspire so that more molecules are pushing in one direction than another, causing a grain to zip through the water. Even though atoms are invisible, Einstein had figured out a way to see them at work. “A few scientific papers, not many, seem like magic,” Rigden writes. “Einstein’s May paper is magic.”