The Microwave background radiation is a remnant of the
Big Bang, an ambient background heat residue like the afterglow of a fire. It's temperature is about 2.7 Kelvin, not far above
absolute zero, and dropping slowly. It's the average temperature of the universe, or pretty close to it.
In the beginning, the universe was
small, and very, very
hot. Now, it's
big, and much, much,
colder. So the
temperature has dropped, to so low where it's very hard to find.
In fact, it was first discovered by some
Bell Labs people in
New Jersey who were working on a microwave
communications antenna. They were very
dilligent in the jobs, and managed to
filter out just about all the
static the antenna itself was creating. But they still kept getting a
uniform noise of microwave radiation no matter where they pointed the antenna. Kind of like the white static you see on
TV while
nothing's on. Coincidentally, they had
lunch with some
researchers from
Princeton a few days later, who'd just realized that
theoretically, such a microwave background would have to
exist if the Big Bang happened. Later, the Bell Labs people won a
Nobel prize for this work. (I am told, specifically, that
Arno Penzias won the Nobel for this). Of course, how
factual this story is is anyone's guess; I heard it from my
physics professor, who works in the field.
The
COBE satellite produced a very accurate
map of the microwave background radiation over all the sky, and detected very small temperature variances in it. This was a
good thing, since some sort of
irregularity was needed to explain things like
galaxies and
us. This is because the temperature differences are related to the clumping of matter in the early universe. No clumps, no galaxies.
The microwave background radiation is one of the stronger pieces of
supporting evidence for the big bang. When compared to a standard
blackbody spectrum, this radiation is more perfectly
blackbody than anything we can create in a laboratory. In other words, the
Universe is cooling very much according to
theory.
More
experiments are underway to scan the
radiation with more detail. This information can be used for things such as determining whether the universe will keep on expanding, whether it'll recollapse, or whether it's right in the middle.
In other words, the microwave background radiation is
cool stuff.
A more recent, and more detailed survey of the microwave background was done by the
BOOMERanG Project