In one minute

Santiago, Schuster and Visser analyze generic Natário warp geometries with unit lapse and flat spatial slices in standard general relativity. They calculate the full stress-energy tensor and emphasize that positive energy for one observer family does not establish the weak energy condition. For localized bubbles with suitable Eulerian trajectories returning to asymptotically flat regions, their argument also requires null energy condition violations. The key contradiction is between the monotonic curvature evolution required by that condition and recovery of the original asymptotic geometry after passage. Within these assumptions, null energy condition violation also entails violations of the weak, strong and dominant conditions. Their appendix treats non-unit lapse and curved spatial slices as genuinely different frameworks requiring separate analysis, limiting the scope of the result.

Generic warp drives violate the null energy condition