One universe or many?

Abstract

The debate between cosmological uniqueness and the plurality of worlds reflects shifting historical definitions of what constitutes a physical universe. In antiquity, the Aristotelian-Ptolemaic tradition maintained a unique, finite cosmos, while the Atomists postulated an infinite number of co-existent worlds within an infinite void. Medieval scholasticism revisited this conflict by weighing Aristotelian physics against the theological requirement of divine omnipotence, which arguably necessitated the possibility of multiple creations. The Copernican revolution further transformed the problem by reclassifying the sun as a star, leading to the seventeenth-century conception of multiple planetary systems. By the eighteenth and nineteenth centuries, the focus shifted to the distribution of stars and the nature of nebulae. The subsequent confirmation of extra-galactic systems established a hierarchy of sub-systems—planets, stars, and galaxies—within an increasingly expansive observable universe. Contemporary relativistic cosmology treats the uniqueness of the universe not as an a priori certainty, but as a regulative ideal for empirical inquiry. Uniqueness remains a standard of systematic integration subject to continual revision as observational horizons expand. Consequently, the term “universe” functions as a material identification that evolves alongside advancements in astronomical observation and physical theory. – AI-generated abstract.