Evidence of a decreasing trend for the Hubble constant

Abstract: The current discrepancy between the Hubble constant $H_0$ derived from the local distance ladder and from the cosmic microwave background is one of the most crucial issues in cosmology, as it possibly indicates unknown systematics or new physics. Here we present a novel non-parametric method to estimate Hubble constant as a function of redshift. We establish independent estimates of the evolution of Hubble constant by diagonalizing the covariance matrix. From type Ia supernovae and the observed Hubble parameter data, a decreasing trend of Hubble constant with a significance of 5.6$\sigma$ confidence level is found. At low redshift, its value is dramatically consistent with that measured from the local distance ladder, and it drops to the value measured from the cosmic microwave background at high redshift. Our results can relieve the Hubble tension, and prefer the late-time solutions of it, especially the new physics.