On Non-Singular Spacetimes and the Beginning of the Universe

This article examines the philosophical implications of non-singular spacetime models for cosmological arguments concerning the universe's beginning. Sinclair analyzes whether contemporary physical theories that avoid an initial spacetime singularity successfully eliminate the need for a temporal beginning to the universe, thereby undermining certain theistic arguments.

The work engages critically with various non-singular cosmological models, including eternal inflation scenarios, cyclic universes, and emergent spacetime theories. Sinclair argues that while these models may avoid a mathematical singularity at t=0, they do not necessarily escape the philosophical conclusion that the universe began to exist. He distinguishes between mathematical singularities in physical models and the metaphysical question of whether the universe has a temporal beginning in the absolute sense.

Central to Sinclair's analysis is the application of the Borde-Guth-Vilenkin theorem, which demonstrates that even inflationary spacetimes that are geodesically complete to the future must be geodesically incomplete to the past under certain reasonable conditions. He contends that this theorem applies to most viable non-singular models, suggesting they cannot be past-eternal despite avoiding an initial singularity. The article examines specific cases where the theorem's conditions might be violated, arguing that such scenarios either remain physically implausible or still imply a beginning through other considerations.

The work situates itself within the broader dialogue between contemporary physics and natural theology, specifically addressing physicists and philosophers who argue that modern cosmology has rendered obsolete the notion of cosmic beginning. Sinclair challenges authors like Sean Carroll and Anthony Aguirre who propose past-eternal models, demonstrating that their proposals face significant theoretical difficulties when examined closely.

Sinclair's methodology combines technical analysis of cosmological models with philosophical argumentation about the nature of time, causation, and existence. He maintains that the distinction between singular and non-singular spacetimes, while mathematically significant, does not resolve the fundamental metaphysical question about the universe's origin. The article contributes to natural theology by defending the continued relevance of cosmological arguments in light of cutting-edge physics, arguing that scientific advances have not eliminated the need to explain why the universe exists at all.

The analysis reveals how contemporary cosmology, rather than undermining philosophical arguments for theism, continues to raise profound questions about ultimate origins that purely physical descriptions struggle to address comprehensively.