Abstract
The Cosmic Microwave Background (CMB) is the oldest light we can observe, emitted around 380 000 years after the Big Bang. Observations of the CMB reveal tiny temperature fluctuations. These anisotropies contain a wealth of information about the nature and structure of the Universe. They enable us to measure fundamental cosmological parameters, such as the density of dark matter and dark energy, with unrivalled precision. The CMB is also a valuable tool for testing theories of fundamental physics. It is sensitive to a wide range of phenomena, from neutrino masses to the nature of gravity. The most stringent constraints on the CMB currently come from data collected by ESA's Planck satellite. Planck has tested our models of the Universe with extreme precision, answering many questions but also leaving some fundamental mysteries unsolved. Current and future CMB experiments, such as the South Pole Telescope (SPT), Simons Observatory, CMB-S4, Litebird and others, will continue to provide us with valuable information on the origin, evolution and composition of our cosmos.
