Øystein Elgarøy: The A-word

The anthropic principle, or "the A-word", states that the values of the fundamental constants of nature and of the cosmological parameters are conditioned by the fact that they must be so as to allow the existence of conscious observers. This seems like common sense. For example, we certainly could not live in a universe without stable atoms. However, a number of physicists and cosmologists use this principle in attempts to explain things like the unnaturally small value of the cosmological constant which dominates the present expansion rate of the Universe. Such explanations must assume that our universe is only one in a vast ensemble of universes, the so-called multiverse, and that the fundamental physical parameters take on different values in different regions of this multiverse. This is not a new idea, the germs of it extends back to the old Greek atomists, but it raises several questions. Are there any reasons for believing that the multiverse exists? Is the anthropic principle scientific in the sense that it can be falsified? In this seminar which involves almost exclusively the most speculative parts of physics and cosmology I will give examples of anthropic "explanations" and discuss some of the arguments that have been put forward both in favour of, and against, their use in science.