Our Universe

Using Einstein’s Theory of General Relativity and the Cosmological Principle, scientists were able to predict the shape of our universe, since matter is distributed equally, and gravity is distortion in space and time. The universe can only have one of three forms. It can be "positively" curved like the surface of a ball and finite in extent; it can be "negatively" curved like a saddle and infinite in extent; or it can be "flat" and infinite in extent (today’s conception of space).

No one knows how much matter there is in the universe, and as a result it is impossible to determine what type of universe we live in. If the density of matter is less than the so-called critical density, the universe is open and infinite. If the density is greater than the critical density the universe is closed and finite. If the density just equals the critical density, the universe is flat, but still presumably infinite. In this universe, given enough time, the inertia of the expansion of the universe will eventually be less than the force of gravity. The universe begins to recede and compact. Another Big Bang results when the universe is small and dense enough. The value of the critical density is very small: it corresponds to roughly 6 hydrogen atoms per cubic meter.