The Weak Anthropic Principle

The approach which does the least violence to conventional modes of scientific thought is to invoke a Weak Anthropic Principle (WAP). Barrow and Tipler describe it thus:

The observed values of all physical and cosmological quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirement that the Universe be old enough for it to have already done so.’

In other words, our existence as observers functions as a cosmological selection effect. There can be no observations without observers. Our observations must satisfy the conditions necessary for our existence.

However, the WAP does not take us very far towards an explanation of the observed coincidences. In conjunction with a conventional Big Bang cosmology, it still gives the impression that our existence is an accident of vanishingly small probability. Thus, in practice, it usually appears in conjunction with a cosmological model which suggests that there is a sense in which all possible universes actually exist. See Many-Universes Models and Analysing the Anthropic Arguments.

Email link | Feedback | Contributed by: Dr. Christopher Southgate
Source: God, Humanity and the Cosmos  (T&T Clark, 1999)