Cosmic microwave background

The cosmic microwave background is the afterglow of the Big Bang, revealing the universe's infancy at a temperature of 2.7 K.

About this subject

The cosmic microwave background (CMB) is electromagnetic radiation that fills the universe, a relic from the time when the cosmos became transparent, about 380,000 years after the Big Bang. Discovered accidentally in 1965 by Arno Penzias and Robert Wilson while using a radio antenna at Bell Labs in the United States, this microwave signal was interpreted as the definitive confirmation of the Big Bang theory, earning them the Nobel Prize in Physics in 1978.

The CMB exhibits an almost perfect blackbody spectrum, with an average temperature of 2.725 Kelvin. Tiny temperature fluctuations, on the order of one part in 100,000, have been mapped by space missions such as COBE, WMAP, and Planck. These fluctuations are the seeds of large-scale structures in the universe, such as galaxies and galaxy clusters, formed over billions of years by gravity.

Beyond providing the earliest snapshot of the universe, the CMB allows precise testing of cosmological models. The composition of the universe, including the abundance of dark matter and dark energy, is inferred from the anisotropies of the CMB. For example, data from the Planck satellite, launched in 2009, indicate that the universe is 13.8 billion years old and that dark energy makes up about 68% of the total cosmic content.

The CMB also serves as a tool to investigate physics beyond the standard model, such as cosmic inflation and possible variations in fundamental constants. Recent studies, like those from the BICEP telescope, aim to detect primordial gravitational wave signals imprinted in the CMB polarization, which would open a direct window into the first moments of the universe.

Frequently Asked Questions

What is the cosmic microwave background?

It is the afterglow of the Big Bang, a faint glow filling the universe, detected as microwaves with a temperature of about 2.7 K.

How was the cosmic microwave background discovered?

It was discovered accidentally in 1965 by scientists Arno Penzias and Robert Wilson, who were testing a radio antenna and found an unexplained background noise, later identified as the CMB.

Why is the cosmic microwave background important for cosmology?

It provides the oldest image of the universe, confirms the Big Bang model, and its temperature fluctuations contain information about the composition and evolution of the cosmos, including dark matter and dark energy.