Cosmology of the physical universe
September 7, 2012 at 11:29 pm
(This post was last modified: September 7, 2012 at 11:30 pm by Jackalope.)
I'm finding the usual 'atheist vs theist deathmatch" threads a bit tiresome these days, and thought I'd start a thread for sharing information and discussing aspects of physical cosmology. While metaphysical and theological cosmology are certainly valid topics at AF, let's keep this thread's scope to physical cosmology please (feel free to start your own thread on other-than-physical cosmology).
I'll start with a short summary of the Cosmological Principle. I'll periodically add to this thread in easily digestible portions. Feel free to add your own comments and questions.
The Cosmological Principle
Digested from the Wikipedia article on the Cosmological Principle and other sources.
Issac Newton is credited with first clearly asserting the principle, usually stated as:
The principle contains three implied qualifiers:
Furthermore, the principle has two testable consequences:
Current observational evidence supports both homogeneity and isotropy (in the interests of keeping this post from being TL;DR it will be left as a point for discussion). Past discoveries that at first appeared to contradict homogeneity or isotropy have been resolved by later discoveries (also left as a point for future discussion).
I'll start with a short summary of the Cosmological Principle. I'll periodically add to this thread in easily digestible portions. Feel free to add your own comments and questions.
The Cosmological Principle
Digested from the Wikipedia article on the Cosmological Principle and other sources.
Issac Newton is credited with first clearly asserting the principle, usually stated as:
"Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers."
The principle contains three implied qualifiers:
- "Observers" - means any observer at any location in the Universe, not just on Earth.
- "Looks the same" - refers not to appearance of physical structures, but rather the effects of physical laws in observable phenomena.
- Variation in physical structures can be overlooked - provided that said variation does not imperil the uniformity of conclusions drawn from observation.
Furthermore, the principle has two testable consequences:
- Homogeneity - the same observational evidence is available to all observers. In other words, what is observable by us is a fair sample.
- Isotropy - the same observational evidence is available in any direction. That is to say that the same physical laws apply throughout the universe.
Current observational evidence supports both homogeneity and isotropy (in the interests of keeping this post from being TL;DR it will be left as a point for discussion). Past discoveries that at first appeared to contradict homogeneity or isotropy have been resolved by later discoveries (also left as a point for future discussion).
