According to the theory, therefore, our own little patch of the cosmos should
appear geometrically "flat," the way a section of a balloon looks flat when
viewed close up. This was the universe long thought to be the most beautiful
and simple.

But it required, by the logic of Einstein's general relativity, that there be
much more dark matter, or something, to the universe, enough to "flatten"
space-time, than astronomers had found.


http://www.nytimes.com/2002/07/23/science/space/23UNIV.html?pagewanted=3&8isc