Cosmic microwave background

The cosmic microwave background (CMB) is the afterglow of the Big Bang, a relic from the early universe that fills the cosmos.

About this subject

The cosmic microwave background (CMB) is the oldest light we can observe, emitted about 380,000 years after the Big Bang. At that time, the universe had cooled enough for protons and electrons to combine into neutral atoms, allowing photons to travel freely. This radiation was predicted theoretically in the 1940s and accidentally discovered in 1965 by scientists Arno Penzias and Robert Wilson, who later won the Nobel Prize for their discovery.

The CMB fills the entire sky almost uniformly, with an average temperature of 2.725 kelvins (about -270 °C). Tiny temperature fluctuations, on the order of one part in 100,000, have been precisely mapped by missions such as the COBE satellite (1989), the WMAP probe (2001), and the Planck space telescope (2009). These fluctuations are the seeds of cosmic structures: galaxies, clusters, and superclusters we see today.

Studying the CMB provides crucial information about the composition of the universe, including the proportions of dark matter, dark energy, and baryonic matter. It also confirms the Big Bang model and the theory of cosmic inflation, which proposes an exponential expansion in the first moments of the universe. The radiation has a perfect blackbody spectrum, strong evidence of its primordial origin.

Interestingly, the CMB is not visible to the naked eye but can be detected by specialized radios and telescopes. Its name comes from the fact that microwaves are the wavelength at which the radiation peaks today, due to cooling from the expansion of the universe (redshift).

Frequently Asked Questions

What is the cosmic microwave background?

It is the leftover radiation from the Big Bang, emitted when the universe was about 380,000 years old. It fills all of space and has an average temperature of 2.7 K.

Who discovered the CMB?

Arno Penzias and Robert Wilson in 1965, in the United States, while working with a radio antenna. They received the Nobel Prize in Physics in 1978.

Why is the CMB important for cosmology?

It provides evidence for the Big Bang, allows measurement of the universe's composition, and reveals fluctuations that seeded galaxies. It is a key tool for understanding the origin and evolution of the cosmos.