"Sometimes I'm looking at the gutter and sometimes the stars. But when we (the collective we) do look at the sky, what we see is tremendous. The cosmic background radiation is one of those remarkable discoveries that will mark the century. The last century, that is. ... The cosmic background radiation dies in fact fill the sky and on average appears to be completely thermal: that is, it can be completely characterized by the temperature alone. The cosmic background radiation looks exactly like a hot bath of light left over from the big bang. Only it's not so hot anymore, just a few degrees [about 2.7 degrees Centrigrade - a63] above absolute zero.
After the COBE [Cosmic Background Explorer] satellite a generation of cosmologists became slaves to the cosmic background radiation. Superb experiments are built to perform measurements of all kinds. ...
According to the Heisenberg uncertainty principle, quantum particles and fields cannot be perfectly still. A consequence is that there will always be quantum fluctuations where the local quantum energy will be slightly higher or slightly lower than average. ... The overall effect is a patterning of the cosmic background radiation with minute hot and cold spots. ...
This arehaeological remnant of the big bang has journeyed from the farthest reaches of the cosmos that we can access and carries information about these earliest times, and so encodes all kinds of information about the large-scale landscape of the universe. In particular, we should be able to see an imprint of the geometry of space in the pattern of hot and cold spots in the sky.
We can see how the universe got its spots."
- Janna Levin, How the Universe Got Its Spots
Here's another image of the Cosmic Microwave Background. I just think it's incredibly neat. This image was produced a couple of years ago, after Janna Levin's book was published; it is from one of the "superb experiments" she mentioned in this passage, written in January 2000. 