On the Infeasibility of Low-Energy Warp Drive via Metamaterial Gravitational Coupling

Recent “low-energy” warp-drive concepts propose replacing the constant gravitational coupling with a spatially varying scalar field set by an engineered metamaterial’s
electromagnetic response. We show that the idea fails on both theoretical and experimental grounds. A prescribed, non-dynamical κ(x) in the field equation Gμν = κ(x)Tμν clashes with the contracted Bianchi identity, ∇μGμν ≡ 0, forcing ∇μTμν ̸= 0 and thus violating local energy–momentum conservation. Making κ(x) dynamical yields a scalar–tensor theory in which the scalar mediates a new long-range force that breaks the strong equivalence principle; Solar-System and pulsar-timing experiments already restrict |γ − 1| ≲ 10−5, excluding any technologically useful coupling. Junction-condition analysis further shows that any interface where κ changes demands a δ-function layer of stress–energy, while even steep continuous profiles are ruled out by torsion-balance, lunar-laser, and spacecraft Doppler measurements. Hence the concept is untenable: a non-dynamical scheme violates conservation laws, and its scalar-tensor completion is falsified by existing data.