Abstract
Without any additional physical inputs, Einstein's equations become almost tautological, permitting virtually all spacetimes as solutions. Typically, various energy conditions, reflecting the positivity of local matter-energy, are used to constrain these solutions. I will argue that this is a mistake: the energy conditions do not come from matter at all. Instead, I will proposal two possible alternatives that could determine which spacetimes are physically allowed and which are forbidden.
Maulik Parikh