Asked by: Theodore, Herne Hill

Astronomers already can see the light from the Big Bang, or at least the first light formed after the Big Bang occurred. It is called the ‘cosmic microwave background’ (CMB).

The first photons were created around 10 seconds after the Big Bang, but were initially unable to travel because they were constantly interacting with subatomic particles. It was only after those subatomic particles combined to form atoms, about 378,000 years after the Big Bang, that the photons were able to propagate through the Universe. The CMB is the relic radiation from that time.

Since then, the Universe has cooled and expanded. This has ‘redshifted’ the CMB light so that today it appears as a background glow which is brightest in the microwave region of the electromagnetic spectrum.

Using radio telescopes such as the Planck satellite, astronomers now have high-resolution maps of the CMB, which encode important details of the Universe’s early history.

Read more:

Subscribe to BBC Science Focus Magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.