There Is No Adequate Definition of ‘Fine-tuned for Life’
The discovery that the universe is fine-tuned for life – a discovery to which the phrase ‘the anthropic principle’ is often applied – has prompted much extra-cosmic speculation by philosophers, theologians, and theoretical physicists. Such speculation is referred to as extra-cosmic because an inference is made to the existence either of one unobservable entity that is distinct from the cosmos and any of its parts (God) or of many such entities (multiple universes). In this article a case is mounted for the sceptical position that cosmic fine-tuning does not support an inference to anything extra-cosmic. To that end three definitions of ‘fine-tuned for life’ are proposed: the ‘slight difference’ definition, the (unconditional) probability definition, and John Leslie’s conditional probability definition. These three definitions are the only ones suggested by the relevant literature on fine-tuning and the anthropic principle. Since on none of them do claims of fine-tuning warrant an inference to something extracosmic, it is concluded that there is no definition of ‘fine-tuned for life’ serving this function.