[4] In quantum theory, the uncertainty principle allows the vacuum of space to be filled with virtual particle-antiparticle pairs which appear spontaneously and exist for only a short time before, typically, annihilating themselves again.
In the Casimir effect, two flat plates placed very close together restrict the wavelengths of quanta which can exist between them.
[5] It is possible to arrange multiple beams of laser light such that destructive quantum interference suppresses the vacuum fluctuations.
The repetitive waveform of light leads to alternating regions of positive and negative energy.
This theory was developed to explain the anomaly of negative-energy quantum states predicted by the Dirac equation.
A year later, after work by Weyl, the negative energy concept was abandoned and replaced by a theory of antimatter.
A wormhole directly connects two locations which may be separated arbitrarily far apart in both space and time, and in principle allows near-instantaneous travel between them.
[10] A theoretical principle for a faster-than-light (FTL) warp drive for spaceships has been suggested, using negative energy.
The Alcubierre drive is based on a solution to the Einstein field equations of general relativity in which a "bubble" of spacetime is constructed using a hypothetical negative energy.