Eternal return Eternal return (also sometimes known as eternal recurrence) refers to the idea that the universe runs in an infinite cycle. Eternal return (ewige wiederkehr des gleichen) was popularised by Friedrich Nietzsche in Ecce Homo - and elsewhere. Nietzsche reportedly got the idea from Heinrich Heine. If the space-time is everywhere finite, discrete and reversible, eternal return is an inevitable consequence. This would happen in a finite universe, where finite nature holds, and reversibility is always and everywhere true. Other sites cover the concept in more detail than it is appropriate to go into here - e.g. [here]. Eternal return is a sort of finite and discrete equivalent to the Poincare Recurrence Theorem. For more details about that, see [here]