Cosmological Principle
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The Cosmological Principle is not a principle, but rather a reasonable assumption or axiom that severely restricts the large variety of possible cosmological theories. It follows from the observation of the Universe on a large scale, and states that:
- On large scales, the Universe is homogeneous and isotropic.
[edit] Explanation
The Cosmological Principle means that the universe, when viewed on sufficiently large distance scales, has no preferred directions or preferred places. Or, in other words, on a large scale the Universe looks the same in all directions for an observer at any place. This principle is consistent with observations of the universe from the Earth. In regard to the observations, the principle states that Earth is nowhere special (the Copernican principle).
A challenge to this account comes from the problem of induction: empirical observations of patterns occurring within a limited scope (in this case, the observed universe) can shed no special light on the state of things outside that scope. Heterogeneous spaces often contain (irregularly and unevenly distributed) homogenous and isotropic masses; we cannot be certain that we are not situated in such a homogenous and isotropic mass (of a scale exceeding the limits of our observation, and thereby accounting for our observations of homogeny and isotropy), itself situated in a larger, heterogeneous universe.
[edit] Support
- Observed isotropy of the cosmic microwave background radiation (CMB), combined with the Copernican principle [1]
