One of the most remarkable stories you will hear about the physicist's quest to prove Ernst Mach's theories. In Nautilus, Amanda Gefter describes to us a fascinating "three-men play" featuring no other than physicists Albert Einstein, Ernst Mach and Michele Besso. The Italian became a "sidekick of sorts" to Einstein and introduced him to Mach's works — an instrumental part in completing the German's famous theory of special relativity. "It must have been an unsettling feeling for Einstein—watching his theory gather steam and speed away from him, proving the very thing he had set out to disprove. The problem was that, according to the theory, spacetime geometry was not fully determined by the distribution of matter in the universe, so that even if you removed everything observable, some extra ingredient still remained—spacetime itself, dynamic yet absolute. It created an unbridgeable divide between the physical world and the mind, inviting, in its realist stance, a whiff of pure belief, even mysticism—the belief in a four-dimensional substratum, the paper on which reality is drawn, though the paper itself is invisible."