ABSTRACT
Anthropic reasoning aims to express the links between the kind of observers and the kind of physical conditions they observe. Any observers that require a narrow range of physical conditions to survive could apply anthropic reasoning. Anthropic reasoning is best captured in weak anthropic principle (WAP), which says physical observers will not be distributed randomly in space and time. Sustainable forms of the strong anthropic principle (SAP) generalize WAP to the universe, and so support the existence of a 'multiverse' of many discrete physical universes. Less sustainable versions import teleological implications and argue that the universe was preprogrammed for generating life. The Bayesian view of statistics can be controversial, and things are more clear-cut when observers know that an ensemble of outcomes exists, so that probability can be defined simply via relative frequency. In modern cosmology, where the preferred models inevitably create a multiverse of causally disconnected bubbles, each of which can display different forms of the 'laws of physics'.
