Observer-robust energy condition verification for warp drive spacetimes

Abstract

Whether a warp drive metric requires exotic matter is decided by energy conditions quantified over all observers, not only the Eulerian. Each of the null, weak, strong and dominant conditions is equivalent, at a point, to feasibility of a $4\times4$ linear matrix inequality $A_{ab}+σg_{ab}\succeq0$, by the S-lemma, with $A_{ab}$ the stress-energy tensor or its trace reverse and the dominant condition a conjunction of two such tests. It forms no eigendecomposition of $T^a{}_b$, imposes no rapidity cap and assumes no Hawking-Ellis type, so it decides all four alike, Types I and IV not being exhaustive; its multiplier margin is exactly half the null-cone minimum, so the same test returns the severity. Composed with an interval enclosure of the curvature chain it decides a point from the metric itself, not from a floating-point copy of its stress-energy. At Type I each condition reduces instead to an eigenvalue inequality holding for all observers at once. The type label is numerical and tolerance-bound; the reported severities are rapidity-capped diagnostics, not certificates. Everything decided uses only boost-invariant data and stays well posed through $v_s=1$. On a flat slice the Eulerian momentum that opens the Type-IV wall vanishes only for a gradient shift, so among four matched drives the irrotational Rodal geometry is Type I identically, its shift curl-free by an exact profile identity, while Alcubierre and Natário are Type-IV dominated at every sampled speed and Van den Broeck above its transition. A single-frame reading of Rodal misses about 73% of its wall weak-energy violations. All four violate the pointwise null energy condition at every sampled speed, consistent with the Santiago-Schuster-Visser no-go, whose null step is conditional. Both are realized in warpax, a JAX toolkit building $T^a{}_b$ by automatic differentiation.