Physical Society Colloquium

Special Physical Society Colloquium

Quantum mechanics and the equivalence principle

Paul Davies

Beyond: Institute for Fundamental Concepts in Physics
Arizona State University

The general theory of relativity rests on the principle that test bodies of different mass fall equally under gravity. However, in quantum mechanics the mass does not scale out of a description of a particle moving in a gravitational field. This raises the surprisingly subtle question of how the principle of equivalence should be incorporated into quantum mechanics, especially in the case of highly non-classical quantum states. To analyze this problem, I use a model of a quantum clock to calculate the expectation value of the time of flight of a quantum particle in uniform and non-uniform gravitational fields, with surprising results. This topic is now moving into the realm of real and planned experiments.