Big Bang Light Still Fills the Whole Sky

Light from the early universe still reaches Earth from every direction. It is called the cosmic microwave background, and it has traveled for about 13.8 billion years. It began as hot, glowing gas filling all of space. As space expanded, the light stretched from visible and infrared wavelengths into microwaves.

Three space missions mapped it: NASA’s COBE, launched in 1989, then WMAP in 2001 and the European Space Agency’s Planck in 2009, whose map was more than 2.5 times sharper than WMAP’s. COBE’s lead scientists won the 2006 Nobel Prize in Physics. The faint patches in the map are the seeds of galaxies, because the slightly denser regions later pulled in more matter.