Cosmic microwave background

The cosmic microwave background is the afterglow of the Big Bang, a relic from the early universe that reveals its age, composition, and evolution.

About this subject

The cosmic microwave background (CMB) is electromagnetic radiation filling the universe, a remnant from the first moments after the Big Bang. Accidentally discovered in 1965 by Arno Penzias and Robert Wilson, it represents the residual heat from when the universe was only 380,000 years old, before the first stars and galaxies formed.

The CMB has an average temperature of 2.725 K (about -270 °C) and is extremely uniform, but exhibits tiny temperature fluctuations on the order of one part in 100,000. These anisotropies, precisely mapped by satellites such as COBE, WMAP, and Planck, contain crucial information about the universe's geometry, density, and composition. They also served as seeds for the formation of large-scale cosmic structures like galaxies and clusters.

The CMB's spectrum matches that of a perfect black body, confirming the hot Big Bang theory. Measurements show the universe consists of approximately 5% baryonic matter, 27% dark matter, and 68% dark energy. The CMB also provides strong evidence for cosmic inflation, a period of exponential expansion in the earliest instants of the universe. This radiation is observed from all directions, with a dipole caused by Earth's motion relative to the cosmic reference frame.

The study of the CMB remains an active research area, with ongoing experiments to measure polarization and search for primordial gravitational waves. These investigations may reveal the universe's first moments, test quantum gravity theories, and refine our understanding of cosmic evolution.

Frequently Asked Questions

What is the cosmic microwave background?

It is the electromagnetic radiation left over from the Big Bang, filling the universe with an average temperature of 2.725 K. Discovered in 1965, it is the strongest evidence for the Big Bang.

Why is the CMB so uniform?

Its uniformity is explained by cosmic inflation, a rapid expansion in the early universe that smoothed out temperature. Tiny fluctuations serve as seeds for cosmic structures.

What do CMB anisotropies tell us?

They reveal the universe's composition (dark matter, dark energy), its flat geometry, age (about 13.8 billion years), and support inflation models.