Can we see the Big Bang’s afterglow?

Fluctuations in the cosmic microwave background
Credit: ESA and the Planck Collaboration

The cosmic microwave background, discovered in 1965, is the radiation left over from the Big Bang. It has been mapped in great detail by satellites. Tiny temperature fluctuations reveal the seeds of the Universe’s large-scale structure.

Large-scale structure of the Universe
Structure growth: The large-scale structure of the Universe, with its huge clusters and voids, grew from the tiniest quantum fluctuations during the Big Bang (simulation).
Credit: Project Horizon
Life of a photon
Travel restrictions: In the early Universe, light (blue) could not travel far before being absorbed by charged particles (red and green).
Credit: NASA/JPL-Caltech
Polarising view of cosmic microwave background
Polarising view: Subtle polarisation patterns in the cosmic microwave background may reveal details about the very first events in the Universe.
Credit: ESA and the Planck Collaboration

In 1965, radio astronomers Arno. Penzias and Robert Wilson accidentally discovered a faint, almost uniform glow of microwave radiation. This cosmic microwave background (CMB) is the afterglow of the Big Bang. It was produced when the Universe was some 380 000 years old, and had cooled down enough for photons (light particles) to travel freely through space. Tiny deviations from the CMB’s average temperature of -270.4° C are produced by small density fluctuations in the early Universe – the seeds of clusters of galaxies.

Enhanced vision
Enhanced vision: Three satellites – COBE, WMAP and Planck – provided ever sharper views of the temperature fluctuations in the cosmic microwave background.
Credit: NASA/JPL-Caltech/ESA
Perfect match
Perfect match: Measurements of the energy distribution of the cosmic microwave background (crosses) perfectly match theoretical expectations (solid line).
Credit: design und mehr

The newborn Universe was very hot. It produced a lot of energetic radiation. That radiation has cooled down ever since, but it can still be observed. The cosmic microwave background is the afterglow of the Big Bang.