Cosmology, Page 101: [Previous Page] [Next Page] [Class Home Page] Textbook pages 462 - 469

The Cosmological Principle

Why does everything expand directly away from US? Are we at the center of the Universe? Why are more distant objects expanding faster?

Many times in this class we have talked about man's perception that we are somehow special in the Universe. And again and again, we find we are not. In order to study the universe will have to make one assumption! That is, the Uniformity of Nature. The physical laws we know on Earth (gravity, speed of light, etc), apply everywhere else in the universe.

This principle, referred to as the Cosmological Principle, states that the universe is:

1. Homogeneity. There is no preferred observing position in the universe. (nor are WE at any preferred observing position!)
2. Isotropy. We see no difference in the structure of the universe as we look in different directions.






So how do we explain our central position in the expansion?

In the above "Raisin Bread" analogy, as the bread rises, each raisin sees the other raisins moving away from it.. A raisin which started out twice as far, will have to move twice as FAST!