The Big Bang

An old story goes that if you look at the sky during a clear, crisp night, and challenge yourself in counting all the stars, when you will have counted them all, the spell says that this will bring you Death. Now we know that this is a rather accurate statement, since there are a few hundred billion sun-like stars in our own Milky Way (a galaxy, or group of stars) alone, and, by counting them one per second, it would take a few thousand years!

An image of globular cluster M13, containing perhaps more than 100,000 stars. It is about 25,000 light years from us.

If we look at the picture above, the famous Olber's paradox (1826) comes to mind. (Actually, the paradox was formulated before Kepler). The riddle goes like this: assume that the universe is uniform and infinite. Then, it should be as bright as our Sun, because it is filled with stars in all directions. It is true that distant stars look dim ( the intensity of light decreases as the square of the distance), but on the other hand, there are more distant stars than close ones (the number of distant stars grows with the square of the distance); thus the two distance dependencies cancel out, and one gets that the sky should be as bright as the Sun. Obviously it is not. What is wrong with the argument above?

For more information, check the SEDS page of the Messier catalog