With a cold, dark whimper. As the universe continues to expand, galaxies will recede farther and farther until they’re impossible to see. Stars will stand alone in the cosmos and burn out, leaving behind utter darkness. Galaxies will break apart. Black holes will evaporate. The universe will become a gassy soup of tiny elementary particles. And then, after 10^1000 years, it will use up the last of its energy and reach thermodynamic equilibrium: cold, empty, dead. It’s possible that if the universe continues expanding, every known atom—including your atoms—will simply be torn apart. (Astronomers call this “The Big Rip.”) Anyway, how’s your day going?