In one minute

S. Krasnikov studies spacetime shortcuts, a class including the Alcubierre bubble, the Krasnikov tube and certain wormholes, that permit superluminal travel in a strictly defined sense. Such shortcuts had been suspected impossible, because quantum inequality calculations suggested Planck-scale energy densities and huge total negative energy. He argues these spacetimes may be entirely physical. With explicit examples he proves that the relevant quantum inequality does not always force large energy densities, that large densities need not give large total negative energy, and that such totals can be physically meaningless and need not exclude shortcuts.

The quantum inequalities do not forbid spacetime shortcuts