Cosmic microwave background

The cosmic microwave background is the oldest light in the universe, emitted 380,000 years after the Big Bang.

About this subject

The cosmic microwave background (CMB) is the electromagnetic radiation filling the entire observable universe. It was emitted about 380,000 years after the Big Bang, when the universe cooled enough for protons and electrons to combine into neutral hydrogen atoms. This event, called recombination, allowed photons to travel freely through space, resulting in the CMB we observe today.

Discovered accidentally in 1965 by radio astronomers Arno Penzias and Robert Wilson, the CMB is a central prediction of the Big Bang model. Their discovery earned the Nobel Prize in Physics in 1978 and provided crucial evidence against alternative theories like the steady state. The CMB has a nearly perfect blackbody spectrum with an average temperature of 2.725 K, with tiny temperature fluctuations on the order of 1 part in 100,000.

These anisotropies, precisely mapped by the ESA's Planck satellite (2009-2013), reveal the seeds of cosmic structures, the slightly denser regions that would give rise to galaxies and galaxy clusters. Detailed study of the CMB allows cosmologists to determine fundamental parameters of the universe, such as its age (13.8 billion years), composition (about 5% baryonic matter, 27% dark matter, and 68% dark energy), and geometry (flat).

The CMB is observed across the entire sky, most easily detected at microwave frequencies between 30 and 300 GHz. Telescopes like WMAP (NASA) and Planck have mapped its fluctuations down to angular scales of a few degrees. The polarization of the CMB also carries information about primordial gravitational waves, one of the main focuses of current cosmology.

Frequently Asked Questions

What is the cosmic microwave background?

It is the electromagnetic radiation left over from the Big Bang, emitted when the universe was only 380,000 years old. It fills all space and has an average temperature of 2.725 K.

Why is the CMB important for cosmology?

It provides direct evidence of the Big Bang and contains information about the universe's age, composition, and geometry. The tiny temperature fluctuations are the seeds of galaxies.

How was the CMB discovered?

It was discovered accidentally in 1965 by Arno Penzias and Robert Wilson while trying to eliminate noise from a radio antenna. They won the 1978 Nobel Prize in Physics for the discovery.