Determination of H0 through monitoring of gravitationally lensed quasars

Abstract

Cosmology is the study of the universe as a whole, in particular its physical origin and evolution. According to the current understanding, the universe came into existence some 13.7 billion years ago in a Big Bang (a very hot and very dense state) and has expanded and cooled since then. After about 380,000 years, ions and electrons combined to form the first atoms. At the end of this recombination epoch, the universe became transparent to the photons that could then travel freely. The photons released after recombination formed a thermal radiation that is still observed today in the Cosmic Microwave Background (CMB), with a current temperature of 2.73 K and discovered by Penzias & Wilson (1965) . Matter then slowly assembled in the expanding universe. The first stars, galaxies and active galactic nuclei were formed and started to radiate photons, and thereby re-ionizing the universe. The large structures observed today were finally progressively created. There are three major observations that support the Big Bang theory, namely, CMB, primordial nucleosynthesis and the expansion of the universe.