Cosmic background radiation

Cosmic background radiation is a special kind of electromagnetic radiation that fills all of space. It includes a part called the cosmic microwave background. This microwave radiation comes from old photons that have traveled since the Universe could first let light through. Finding this radiation helped scientists learn more about the Big Bang.

This background radiation looks mostly the same everywhere, but there are very small differences. These match where galaxy filaments and empty spaces called voids are found. It was discovered by accident in 1965 and showed that the early universe was very hot and filled with radiation.

We can see background radiation in many kinds of light, such as infrared and X-rays, but it is strongest in microwaves. Changes in the radiation help scientists learn about the amount of normal matter in the universe. There are also other types of background radiation, like the cosmic neutrino background and extragalactic background light. The Sunyaev–Zel'dovich effect shows how this radiation changes when it passes through clouds of electron particles.

Timeline of significant events

In 1896, a scientist named Charles Édouard Guillaume thought that the heat from stars was about 5.6 K. In 1926, another scientist, Arthur Eddington, believed that the light from stars in our galaxy had a temperature of about 3.2 K. In the 1930s, Erich Regener figured that the energy from cosmic rays in our galaxy was around 2.8 K.

In 1931, the word "microwave" was first used in a book. In 1946, Robert Dicke guessed that microwave background radiation would have a temperature of about 20 K, but later thought it might be closer to 45 K. Around the same time, George Gamow guessed it might be 50 K.

By 1965, Arno Penzias and Robert Woodrow Wilson measured the temperature of this radiation to be about 3 K. This helped scientists learn more about the Big Bang, the start of our universe.