Dictionary of Distances, Michel-Marie Deza, Elena Deza, pp. 337, Elsevier, 2006, ISBN 978-0-444-52087-6, ... The Alcubierre metric is a solution to the Einstein field equation, representing warp drive space-time in which the existence of closed time-like curves is allowed ...
The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity, David Darling, pp. 14, John Wiley & Sons, 2003, ISBN 978-0-471-46771-7, ... matter with a negative energy density. Such matter, known as exotic matter, is the same kind of peculiar stuff apparently needed to maintain stable wormholes ... Quantum mechanics allows the existence of regions of negative energy density under special circumstances, such as in the Casimir effect ...
