anthropic principle

The recognition that only a limited number of all the theoretically possible universes are favourable to the emergence of life. In theory, a large range of universes with different physical properties and values of the constants of nature could existw. The anthropic principle states that only a restricted class of such models can have intelligent observers. Since we exist, the universe we inhabit must have characteristics within the narrow range that has permitted our evolution. This basic expression of the anthropic principle is not generally regarded as controversial, and is sometimes called the weak anthropic principle. The so-called strong anthropic principle, proposed by Brandon Carter, is more speculative. This asserts that, because there are so many apparently unconnected coincidences in nature, which together have made it possible for life to develop, the universe must give rise to observers at some stage in its development.