My Interests Are in Theoretical Cosmology and Quantum Gravity. the Central Principles of Quantum Mechanics and of General Relativity (Our Classical Theory of Gravity) Come Into Sharp Conflict at the Horizon of a Black Hole. Quantum Mechanics Rests on the Principle of Unitarity: Information Cannot Be Fundamentally Lost. General Relativity is Based on the Equivalence Principle: Empty Space Should Look the Same Everywhere and to Everyone.

Black Holes Evaporate, Converting Their Energy Into a Cloud of Radiation. Quantum Mechanics Requires This Cloud to Contain Information: in Principle, We Could Measure the Cloud and Use a Powerful Computer to Reconstruct What Formed the Black Hole. Meanwhile, in General Relativity, the Horizon of a Black Hole is Empty Space, So It Should Look the Same as Empty Space Everywhere Else.