Geometric Spacetime is Boundless, Perceptual Spacetime is Bounded: A New Cosmological Paradigm Based on Total Reflection of Vacuum Medium

The traditional ΛCDM standard cosmological model faces multiple crises, including dark energy fine-tuning, zero detection of dark matter particles, the Big Bang singularity, and JWST early galaxy anomalies. Based on the first principle of global vacuum medium angular momentum conservation, this paper proposes a dualistic cosmology of "geometric spacetime - perceptual spacetime": geometric spacetime is an infinite flat three-dimensional Euclidean background space, boundless and without a beginning; perceptual spacetime is the finite spherical vacuum medium system we observe through electromagnetic waves, whose boundary is a transition region where the medium density decays exponentially to zero. All electromagnetic waves undergo total internal reflection when reaching the boundary and can never escape the medium system, resulting in the finite bounded nature of the universe we perceive. This model does not require any additional assumptions such as dark energy, dark matter, or cosmic inflation, can quantitatively reproduce all classical astronomical observations, perfectly explains multiple observational anomalies that the standard model cannot account for, and puts forward falsifiable unique predictions, providing a simpler and more self-consistent new paradigm for cosmological research.