Why study the Cosmic Microwave Background?
Since light travels at a finite speed, astronomers observing distant objects are looking into the past. Most of the stars that are visible to the naked eye in the night sky are 10 to 100 light years away. Thus, we see them as they were 10 to 100 years ago. We observe Andromeda, the nearest big galaxy, as it was three million years ago. Astronomers observing distant galaxies with the Hubble Space Telescope can see them as they were only a few billion years after the Big Bang. (Most cosmologists believe that the universe is between ten and twenty billion years old.) By observing the cosmic microwave background, cosmologists can study the physical conditions only a few hundred thousand years after the Big Bang, long before stars or galaxies even existed. By study these physical conditions, we can learn about the structure of the universe, its origin and evolution.
