Cosmic microwave background

The Cosmic Microwave Background is the leftover radiation from the Big Bang, mapped by satellites like COBE, WMAP and Planck.

About this subject

The Cosmic Microwave Background (CMB) is electromagnetic radiation filling the entire universe, a remnant from the Big Bang about 13.8 billion years ago. Discovered accidentally in 1964 by Arno Penzias and Robert Wilson, the CMB is one of the strongest pieces of evidence for the Big Bang theory. This radiation began traveling through the cosmos roughly 380,000 years after the Big Bang, when the universe cooled enough for protons and electrons to combine into neutral atoms, allowing light to travel freely.

The CMB has a nearly uniform temperature of 2.725 K (about -270 °C), but tiny temperature fluctuations on the order of 1 part in 100,000 reveal the seeds of future galaxies and galaxy clusters. These anisotropies were precisely measured by ESA's Planck satellite (2009-2013), which mapped the entire sky at multiple frequencies. The CMB map is often depicted in false color, with blue indicating slightly colder regions and red warmer ones, although the differences are minuscule.

Besides confirming the standard cosmological model, the CMB provides fundamental parameters such as the density of dark matter and dark energy, the curvature of the universe, and the Hubble constant. It also allows tests of cosmic inflation theories. In 2014, the BICEP2 team announced detection of primordial B-modes in the CMB, which would have been evidence of primordial gravitational waves, but later studies showed contamination by galactic dust. The study of the CMB remains an active frontier in cosmology.

Frequently Asked Questions

What is the Cosmic Microwave Background?

It is the leftover radiation from the Big Bang, filling the entire universe. Discovered in 1964, it has an average temperature of 2.725 K.

Why is the CMB important for cosmology?

It provides evidence for the Big Bang, reveals density fluctuations that seeded galaxies, and allows measurement of cosmological parameters like dark matter and dark energy densities.

How do satellites map the CMB?

Satellites like COBE, WMAP, and Planck measure the CMB temperature at multiple microwave frequencies, producing all-sky maps with high resolution and sensitivity.