anthropic principle

In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence on Earth of biochemistry, carbon-based life, and eventually human beings to observe such a universe. The common (and "weak") form of the anthropic principle is a truism or tautology that begins with the observation that the universe appears surprisingly hospitable to the emergence of life, particularly complex multicellular life, that can make such an observation and concludes with that premise that in only such a fine-tuned universe can such living observers be.

Given the extreme simplicity of the universe at the start of the Big Bang, the friendliness of the universe to complex structures such as galaxies, planetary systems, and biology is unexpected by any normal model of turbulence driven structuring that science has been able to derive.

The idea evolved from the so-called "Dicke's coincidence", and has subsequently been reinforced by the discovery of many more anthropic coincidences since Robert Dicke first noted that the evolution of the universe is not random, but is coincidentally constrained by biological factors that require that the age of the universe had to be roughly this "golden-age". Much younger, and there would not have been time for sufficient interstellar levels of carbon to build up by nucleosynthesis, but much older, and the golden age of main sequence stars and stable planetary systems would have already come to an end.

The anthropic principle also acts as a convenient category for physical and cosmological reasoning that takes into account the existence of a biosphere on Earth in an essential way. Attempts to invoke the "anthropic principle" to develop scientific explanations has led to more than a little confusion and controversy.

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