Geometry and the Standard Model For decades, the consensus model (ΛCDM) has described the universe as spatially flat (Ω≈1). This conclusion is supported by high-precision data from the Cosmic Microwave Background (CMB) collected by missions like WMAP and Planck, which indicate that the density of matter and energy is perfectly balanced to prevent the universe from curving continuously like a sphere (closed) or a saddle (open). In a flat universe dominated by a constant "dark energy" (the cosmological constant Λ), the expansion accelerates indefinitely, leading to a "Big Freeze" or heat death, where stars burn out and the cosmos becomes cold and dark.

The "Hubble Tension" and New Crises A major crisis known as the Hubble Tension challenges this standard view. Measurements of the expansion rate (H0​) derived from the early universe ( ...