Description
In my essay, I argue that the Copernican Principle (CopP)—the claim that we do not occupy a privileged position in the universe—cannot be justified via Bayesian probabilities. When combined with observed spatial isotropy, CopP provides a deductive argument for establishing the homogeneity of the universe and, consequently, the Cosmological Principle. Thus, a well-founded justification for assuming CopP is of great interest. I begin by discussing different definitions and interpretations of CopP, arguing that the term privilege is problematic due to its metaphysical presuppositions, while the notion of typicality offers a more suitable foundation by shifting the focus from the observer’s spatial position to the observer’s measurements. I conclude that CopP can be interpreted in at least three distinct ways: as a claim about our position, as a claim about the universe’s topology, or as a claim about our observations. I then examine various attempts to justify CopP, reviewing proposed tests based on these interpretations, beginning with those aimed at proving CopP and concluding with those that seek to disprove it. Finally, I analyze a Bayesian approach that combines geometry with probability theory in an attempt to justify CopP. The core idea is that it is improbable for us to occupy a position near the center of symmetry in an inhomogeneous space-time region. However, I argue that this approach ultimately fails, as it shifts the problem from justifying CopP to justifying another assumption—the Equiprobability Principle. Moreover, it raises important questions about the limits of applying probability theory. I conclude that CopP remains an unjustified metaphysical principle—one we have a strong need for to be true but cannot adequately justify through any formal logical framework.
