The Cosmological Principle
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Thu, 22 Sep 2005 00:29:31 GMT
The Cosmological Principle
APM Survey fo a 30 deg. swath of the sky, showing about 1 million galaxies out to a distance of almost 2 billion light years. http://map.gsfc.nasa.gov/ContentMedia/990047b.jpg
After the introduction of General Relativity a number of scientists, including Einstein, tried to apply the new gravitational dynamics to the universe as a whole. At the time this required an assumption about how the matter in the universe was distributed. The simplest assumption to make is that if you viewed the contents of the universe with sufficiently poor vision, it would appear roughly the same everywhere and in every direction. That is, the matter in the universe is homogeneous and isotropic when averaged over very large scales. This is called the Cosmological Principle. This assumption is being tested continuously as we actually observe the distribution of galaxies on ever larger scales. The accompanying picture shows how uniform the distribution of measured galaxies is over a 30° swath of the sky. In addition the cosmic microwave background radiation, the remnant heat from the Big Bang, has a temperature which is highly uniform over the entire sky. This fact strongly supports the notion that the gas which emitted this radiation long ago was very uniformly distributed.
These two ideas form the entire theoretical basis for Big Bang cosmology and lead to very specific predictions for observable properties of the universe. An overview of the Big Bang Model is presented in a set of companion pages.
See: ref: http://map.gsfc.nasa.gov/m_uni/uni_101bb1.html .
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