Page 2, Cosmology Part II: [Previous Page] [Next Page] [Class Home Page] Page 414 - 416

The horizon problem concerns the fact that the Universe is isotropic. No matter what distant corners of the Universe you look at, the sizes and distribution of objects is exactly the same (see the Cosmological Principle).

Under normal expansion, the universe expands at or less than the speed of light. All of the Universe is within our current observable horizon.

How does the Inflationary universe solve the problems of the Big Bang? 1) The tremendous expansion means that the universe is larger than our observable horizon! Most importantly, regions that we see now as widely separated in oppposite directions in the sky were much closer together before inflation and could have been in direct contact, solving the horizon problem.

2) Inflation is like zooming in of some very, very small section of a sphere. If we zoom in to a small enough scale, the sphere will appear flat. Our Universe must be exactly flat for the same reason, it is a very small piece of the larger Big Bang universe. Thus the tremendous expansion greatly dilutes any initial curvature, solving the flatness problem.