Reviewing and delving into the causes of the Hubble tension

Abstract

This paper explores different techniques for measuring the Hubble-Lemaître constant. After reviewing how the measurements of this important cosmological parametre have evolved through history, we present and compare the fundamental methods, both model-independent, based on standard candles/sirens and standard rulers, and model-dependent, based on the cosmic microwave background, where a discrepancy between the two groups of results has been recently named Hubble tension. Sources of systematic uncertainty as well as possible modifications to the ΛCDM model are discussed in order to mitigate this tension.