Cosmic microwave background

The cosmic microwave background (CMB) is the afterglow of the Big Bang, a relic from the early universe that reveals its origin and evolution.

About this subject

The cosmic microwave background (CMB) is the electromagnetic radiation filling the universe, a remnant of the Big Bang. Discovered accidentally in 1965 by Arno Penzias and Robert Wilson, the CMB is one of the strongest pieces of evidence for the Big Bang theory. It corresponds to light emitted about 380,000 years after the universe began, when the primordial plasma cooled enough to form neutral atoms and the universe became transparent to radiation.

The CMB has an almost perfect blackbody spectrum at a temperature of 2.725 K, but exhibits tiny temperature fluctuations on the order of 1 part in 100,000. These anisotropies were precisely mapped by the COBE, WMAP, and Planck satellites, revealing the seeds of cosmic structures: galaxies, clusters, and voids. The CMB map also provides information about the universe's composition: about 5% baryonic matter, 27% dark matter, and 68% dark energy.

The polarization of the CMB, detected by the BICEP experiment and the Planck telescope, offers clues about cosmic inflation, an exponential expansion in the first moments of the universe. Studies of the CMB continue to refine cosmological parameters such as the Hubble constant and the curvature of spacetime, making it a fundamental tool for observational cosmology.

Frequently Asked Questions

What is the cosmic microwave background?

It is the electromagnetic radiation leftover from the Big Bang, filling the entire universe. It was emitted about 380,000 years after the universe began and now has a temperature of 2.7 K.

Why is the CMB important for cosmology?

It provides the oldest image of the universe, with fluctuations that seeded all cosmic structures. It also allows measurements of parameters such as the universe's composition and expansion rate.

How was the CMB discovered?

It was accidentally discovered in 1965 by Arno Penzias and Robert Wilson, who detected an unexplained background noise in their radio antenna. The cosmological explanation was provided by Robert Dicke and Jim Peebles.