What is the cosmic microwave background radiation?

The cosmic microwave background radiation is the afterglow of the Big Bang, filling the universe with low-energy electromagnetic radiation.

The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the entire universe. It is the oldest light in the universe, dating back to just 380,000 years after the Big Bang. The CMB is a remnant of the hot, dense state of the early universe, when matter and radiation were in thermal equilibrium. As the universe expanded and cooled, the radiation was stretched out to longer wavelengths, shifting from visible light to microwave radiation.

The CMB is a crucial piece of evidence for the Big Bang theory, as it provides a snapshot of the universe at a very early stage in its history. The temperature of the CMB is almost uniform across the sky, with tiny fluctuations of about one part in 100,000. These fluctuations are thought to be the seeds of the large-scale structure of the universe, such as galaxies and galaxy clusters.

The CMB has been studied extensively by astronomers and cosmologists, using telescopes and satellites such as the Planck spacecraft. These observations have provided precise measurements of the temperature and polarization of the CMB, which have helped to refine our understanding of the universe's composition, age, and evolution. The CMB is a powerful tool for probing the physics of the early universe and testing theories of cosmology.