Systematic Light Propagation Bias from the Heliosphere and Its Impact on the Hubble Tension

Abstract

The Hubble tension (HT) represents one of the most significant discrepancies in modern cosmology, with local distance measurements yielding $H_0 = 73.5 \pm 1.4$ km/s/Mpc while cosmic microwave background (CMB) observations predict $H_0 = 67.4 \pm 0.5$ km/s/Mpc. We propose that this tension arises from systematic effects introduced by our Solar System's heliospheric (HS) environment on local distance measurements. The HS creates a complex medium of heated plasma and energetic neutral atoms (ENAs) beyond the heliopause (HP), where interstellar medium (ISM) temperatures rise significantly. This thermal gradient and particle environment may systematically affect observations of Cepheid variables and Type Ia supernovae (SNe~Ia) used in the local cosmic distance ladder (CDL), biasing distance measurements and artificially inflating the measured Hubble constant. We present theoretical calculations showing how HS effects could account for up to $\sim 8\%$ of the observed 8--9\% discrepancy, with the realistic contribution lying in the $\sim 3$--$8\%$ range once anisotropy, partial calibration cancellation, and chromatic suppression are included, and discuss observational tests to validate this hypothesis.