In one minute

Eleni-Alexandra Kontou and Ken Olum work on quantum inequalities, bounds on how negative the time-averaged energy density of a quantum field can be. Most were proved in flat spacetime, yet curved-spacetime versions are what decide whether exotic phenomena such as closed timelike curves can exist. Starting from a general inequality by Fewster and Smith, they derive a bound for a minimally coupled scalar field along a geodesic in weakly curved spacetime, to first order in the Ricci tensor. Because only the Ricci tensor appears, paths that meet no matter or energy get no first-order corrections to the flat-space bounds.

Quantum inequality in spacetimes with small curvature