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6.6 Causality violation and semiclassical instability.

4 Connection to dark energy and dark matter.

Some physicists have presented arguments to suggest that a theory of quantum gravity (which would incorporate both theories) would eliminate those solutions in general relativity that allow for backwards time travel ( see the chronology protection conjecture) and thus make the Alcubierre drive invalid. Īnother possible issue is that, although the Alcubierre metric is consistent with Einstein's equations, general relativity does not incorporate quantum mechanics. Some research has claimed that such a concept is possible with purely positive energy using 'soliton' waves. At the close of his original article, however, Alcubierre argued (following an argument developed by physicists analyzing traversable wormholes ) that the Casimir vacuum between parallel plates could fulfill the negative-energy requirement for the Alcubierre drive.

If exotic matter with the correct properties cannot exist, then the drive cannot be constructed. The proposed mechanism of the Alcubierre drive implies a negative energy density and therefore requires exotic matter or manipulation of dark energy. Īlthough the metric proposed by Alcubierre is consistent with the Einstein field equations, construction of such a drive is not necessarily possible. Objects cannot accelerate to the speed of light within normal spacetime instead, the Alcubierre drive shifts space around an object so that the object would arrive at its destination more quickly than light would in normal space without breaking any physical laws. Rather than exceeding the speed of light within a local reference frame, a spacecraft would traverse distances by contracting space in front of it and expanding space behind it, resulting in effective faster-than-light travel. The Alcubierre drive, Alcubierre warp drive, or Alcubierre metric (referring to metric tensor) is a speculative warp drive idea based on a solution of Einstein's field equations in general relativity as proposed by theoretical physicist Miguel Alcubierre during his PhD study at the University of Wales, Cardiff, by which a spacecraft could achieve apparent faster-than-light travel if a configurable energy-density field lower than that of vacuum (that is, negative mass) could be created. Two-dimensional visualization of an Alcubierre drive, showing the opposing regions of expanding and contracting spacetime that displace the central region