What is the cosmic microwave background radiation?

Erik M. Leitch of the University of Chicago explains.
The Cosmic Microwave Background radiotherapy, or CMB for short-circuit, is a faint glow of light that fills the universe, falling on earth from every focus with closely uniform saturation. It is the residual estrus of universe — the afterglow of the boastful knock — streaming through distance these final 14 billion years like the heat from a sun-warmed rock, reradiated at night. Since the early twentieth hundred, two concepts have transformed the way astronomers think about observing the population. The first is that it is fabulously large ; the part of the universe visible today is a sphere closely 15 billion light-years in spoke, and that, we believe, is barely the topple of the iceberg. The irregular is that light travels at a fixed speed. A simple consequence of these ideas is that as you look at more and more distant objects, you ‘re seeing farther and farther back in time — sometimes very far second indeed. When you see jupiter shining in the night sky, for exemplar, you ‘re looking about an hour back in clock, whereas the light from distant galaxies captured by telescopes today was emitted millions of years ago.

The CMB is the oldest lightly we can see — the farthest second both in time and space that we can look. This light set out on its travel more than 14 billion years ago, long before the worldly concern or tied our galax existed. It is a keepsake of the universe ‘s infancy, a time when it was not the cold colored place it is now, but was alternatively a firestorm of radiation and elementary particles. The familiar objects that surround us today — stars, planets, galaxies and the like — finally coalesced from these particles as the population expanded and cooled.

This residual radiation is critical to the study of cosmology because it bears on it the fossil imprint of those particles, a traffic pattern of minuscule volume variations from which we can decipher the critical statistics of the universe, like identifying a defendant from his fingerprint.

When this cosmic background light was released billions of years ago, it was as hot and bright as the surface of a star. The expansion of the universe, however, has stretched space by a factor of a thousand since then. The wavelength of the inner light has stretched with it into the microwave partially of the electromagnetic spectrum, and the CMB has cooled to its contemporary temperature, something the laud thermometers known as radio telescopes record at about 2.73 degrees above absolute zero.

Answer originally posted October 13, 2003.