N ov 2 00 0 Why am I me ? and why is my world so classical ?

This is an attempt to apply Nagel’s distinction between internal and external statements to the interpretation of quantum mechanics. I propose that this distinction resolves the contradiction between unitary evolution and the projection postulate. I also propose a more empirically realistic version of the projection postulate. The result is a version of Everett’s relative-state interpretation, including a proposal for how probabilities are to be understood. Based on a talk given at the 9th UK Foundations of Physics meeting in Birmingham on 12 September 2000. In this talk I want to explore the possibility of a connection between the problem of understanding quantum mechanics and a number of classical philosophical problems. For this purpose, I will at first focus on the measurement problem, which can be given a conveniently concise formulation: the contradiction between the Schrödinger equation and the projection postulate. We appear (at least immediately after reading our first quantum mechanics textbook) to have good reason to believe both of these incompatible statements. The problems to which I want to compare the measurement problem can also be formulated as contradictions between pairs of statements or principles, both of which we seem to have good reason to believe: 1. The existence of space-time vs the passage of time; 2. Determinism vs free will;