This month celebrates the 100th anniversary of Albert Einstein’s publication of the paper laying out what we now refer to as the General Theory of Relativity. Steven Strogatz describes two pivotal moments that Einstein says influenced his way of thinking.

The first involved a compass that his father showed him when he was four or five. Einstein recalled his sense of wonderment that the needle always pointed north, even though nothing appeared to be pulling it in that direction. He came to a conclusion, then and there, about the structure of the physical world: “Something deeply hidden had to be behind things.” The second moment occurred soon after he turned twelve, when he was given “a little book dealing with Euclidean plane geometry.” The book’s “lucidity,” he wrote—the idea that a mathematical assertion could “be proved with such certainty that any doubt appeared to be out of the question”—provoked “wonder of a totally different nature.” Pure thought could be just as powerful as geomagnetism.

Strogatz goes on describe how Einstein’s way of thinking influenced his derivation of a proof of Pythagoras’s theorem and later the development of his major ideas of relativity.