These are the Boltzmann Brains, named after the nineteenth-century physicist Ludwig Boltzmann. These strange late-universe beings will, according to one line of thinking, eventually outnumber every human, otter, alien and android who ever lived or ever will live. In fact, assuming this hypothesis is true, you, dear reader, probably are a Boltzmann Brain yourself. After all, there will only ever be one "real' version of you. But Boltzmann Brains popping into being while hallucinating this moment in your life—along with your entire memory and experiences—they will keep going and going, appearing and disappearing forever in the void.