Adam said: > There's proof and there's proof. As Mr. Baker pointed out, the Big > Bang theory accounts for just about everything we've observed so far > (caveat mine, just in case) about the universe.
Well, sort of. The "Big Bang theory" isn't one theory but really a family of theories. The basic Big Bang framework is the Robertson-Walker metric, which is the solution of Einstein's field equations for a homogeneous, isotropic universe filled with "dust" (which is jargon for matter which exerts no significant pressure). This alone is enough to predict the redshifting of distant objects. You can then construct a specific model by making a choice of what the "dust" really is. The basic choices are radiation and various kinds of matter. You can also add some "vacuum energy" or "cosmological constant". Reasonable choices of such things then predict the microwave background and the abundances of light elements. Tweaking these choices doesn't mean throwing away the Big Bang model as an overall framework. However, there are still some aspects of the large-scale nature of the universe that the basic Big Bang doesn't explain: - The deviations from homogeneity that led to the formation of galaxies. - The origin of isotropy. This is the famous "horizon problem", which arises because regions of the universe that appear to have the same properties should've been causally disconnected early in cosmological history. - The baryon asymmetry (the fact that there is more matter than antimatter). - The reasons why the universe is so close to being "critical" - being balanced between expanding forever and collapsing again. Various extensions of the basic Big Bang model (for example, inflation) and of particle physics (various grand unified models) have been put forward as explanations for these things not explained by the simple Big Bang theories. They haven't yet been explained to my or most other people's satisfaction though. Some people even invoke the "Anthropic Principle" in either its weak or strong form to explain them! Rich GCU Almost There _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
