The Cosmological Principle
Paragraph 1: Cosmologists attempt to understand the origin and structure of the universe as a whole
This assumption that the universe is uniform on a large scale is called “the cosmological principle."
Paragraph 2: the universe is expanding
the evolutionary (Big Bang) theory
the steady-state theory
Paragraph 5: In this special sense, the steady. -state universe itself does not evolve.
Paragraph 3: there was a beginning- -a moment of creation at which the universe came into existence in a hot, violent explosion- the Big Bang
As the explosion evolved, the temperature dropped, the distribution of matter and energy thinned, and the universe expanded
event occurred between ten and twenty billion years ago
uniform not only in space but in time
The steady-state universe would have no beginning and no end
Paragraph 4: “perfect cosmological principle."
To make the steady-state theory compatible with the expanding universe, its proponents introduced the notion of continuous creation.
In an expanding universe, the galaxies move away from each other, spreading matter more thinly over space.
Thus in the steady-state universe there is evolution of stars and galaxies, but the general character and the overall density of the universe remains unchanged over time
Paragraph 6: Both of these views- -steady-state and Bing Bang- allow for cosmic expansion
1,000 times greater than that of a whole spiral galaxy composed of billions of stars
Astronomers determined that almost all quasars are very distant
Paragraph 7: Thus the fact that almost all quasars are very far away implies that earlier in the history of the universe quasars were developing more frequently than they are now.
This evolution is consistent with the Big Bang theory