Why supernova surveys can't reliably find cosmic anisotropy

Searches for cosmic anisotropy using Type Ia supernovae have produced contradictory claims about whether the universe expands at different rates in different directions. This work tests two standard analysis methods—Region Fitting and Hemisphere Comparison—on the Pantheon+ supernova catalog by simulating 2000 sky directions. The finding: current supernova samples can't reliably determine anisotropy directions, not because the universe is isotropic, but because the technique has an intrinsic blind spot. Settling the isotropy question will require larger, more uniformly distributed supernova samples.