Stability

In physics and cosmology, the anthropic principle is the collective name for several ways of asserting that physical and chemical theories, especially astrophysics and cosmology, need to take into account that there is life on Earth, and that one form of that life, Homo sapiens, has attained sapience. The only kind of universe humans can occupy is one that is similar to the current one.

Originally proposed as a rule of reasoning, the term has since been extended to cover supposed “superlaws” that in various ways require the universe to support intelligent life, usually assumed to be carbon-based and occasionally asserted to be human beings. Anthropic reasoning assesses these constraints by analyzing the properties of hypothetical universes whose fundamental parameters or laws of physics differ from those of the real universe. Anthropic reasoning typically concludes that the stability of structures essential for life, from atomic nuclei to the whole universe, depends on delicate balances between different fundamental forces.

These balances are believed to occur only in a tiny fraction of possible universes, so that this universe appears fine-tuned for life. Anthropic reasoning attempts to explain and quantify this fine tuning. Within the scientific community the usual approach is to invoke selection effects and to hypothesize an ensemble of alternate universes, in which case that which can be observed is subject to an anthropic bias.

However, the term anthropic in “anthropic principle” has been argued to be a misnomer. While singling out our kind of carbon-based life, none of the coincidences require human life or demand that carbon-based life develop intelligence.

The anthropic principle has given rise to some confusion and controversy, partly because the phrase has been applied to several distinct ideas. All versions of the principle have been accused of undermining the search for a deeper physical understanding of the universe. Those who invoke the anthropic principle often invoke multiple universes or an intelligent designer, both controversial and criticised for being untestable and therefore outside the purview of accepted science.

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