Vacuum energy extraction

Above the Schwinger limit, very intensive electric fields with field strengths $\mathrm{10^{18} V/m}$, the quantum electrodrodynamical vacuum breaks down, allowing matter to be produced directly from the vacuum - this is known as the Schwinger effect. While purely theoretical at the moment, very-high-power lasers currently being built may be able to exceed the Schwinger limit.

Any matter produced by the Schwinger effect is likely to be extremely miniscule in amount. However, any such matter would in theory gravitate, exerting what may be thought of as an “attractive pull” towards other matter, like a suction pump. This can be described as a negative gravitational pressure, and can be effectively modelled with a negative energy density in the stress-energy tensor. And by the Einstein equations $G_{\mu \nu} = \kappa T_{\mu \nu}$ this would mean a negative Einstein tensor, and thus a negative curvature of spactime. The physical effects of this scenario would be bizarre; instead of experiencing a attractive gravitational force, massive particles would experience a repulsive gravitational force. At the moment, this is purely theoretical; but exploiting this effect may make the Alcubierre Drive (previously discussed) possible, among other applications.