On October 5, 1923, Edwin Hubble sat in the chill of Mount Wilson Observatory, inspecting a glass photographic plate labeled H335H. With a simple red-pen mark, crossing out an "N" for nova and scrawling "VAR!" in ecstatic capital letters, Hubble unlocked the modern cosmos. He had spotted a Cepheid variable star in the Andromeda spiral nebula. Using Henrietta Swan Leavitt's period-luminosity relation, he calculated its distance: Andromeda was not an eddy of gas inside the Milky Way, but an entire island universe millions of light-years out. In a single night, the known cosmos exploded in scale from a solitary galaxy into an infinite sea of them. For a data-driven species, it was the ultimate paradigm shift—proof that our home network was merely one node among billions.