Anthropic interpretation of quantum theory

The problem of interpreting quantum theory on a large (e.g. cosmological) scale has been commonly conceived as a search for objective reality in a framework that is fundamentally probabilistic. The Everett programme attempts to evade the issue by the reintroduction of determinism at the global level of a “state vector of the universe”. The present approach is based on the recognition that, like determinism, objective reality is an unrealistic objective. It is shown how an objective theory of an essentially subjective reality can be set up using an appropriately weighted probability measure on the relevant set of Hilbert subspaces. It is suggested that an entropy principle (superseding the weak anthropic principle) should be used to provide the weighting that is needed. Text for exposition presented at Interdisciplinary Colloquium “La Philosophie de la Nature aujourd’hui?”, Paris, March 2003, and 8th Peyresq Physics Meeting “The Early Universe”, June 2003.