Alcubierre drive

The Alcubierre drive ([alkuˈβjere]) is a speculative warp drive idea according to which a spacecraft could achieve apparent faster-than-light travel by contracting space in front of it and expanding space behind it, under the assumption that a configurable energy-density field lower than that of vacuum (that is, negative mass) could be created.^[1]^[2] Proposed by theoretical physicist Miguel Alcubierre in 1994, the Alcubierre drive is based on a solution of Einstein's field equations. Since those solutions are metric tensors, the Alcubierre drive is also referred to as Alcubierre metric.

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.^[3]

Although the metric proposed by Alcubierre is consistent with the Einstein field equations, construction of such a drive is not necessarily possible. The proposed mechanism of the Alcubierre drive implies a negative energy density and therefore requires exotic matter or manipulation of dark energy.^[4] If exotic matter with the correct properties cannot exist, then the drive cannot be constructed. At the close of his original article,^[5] however, Alcubierre argued (following an argument developed by physicists analyzing traversable wormholes^[6]^[7]) that the Casimir vacuum between parallel plates could fulfill the negative-energy requirement for the Alcubierre drive.

Another possible issue is that, although the Alcubierre metric is consistent with Einstein's equations, general relativity does not incorporate quantum mechanics. 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 backward time travel (see the chronology protection conjecture) and thus make the Alcubierre drive invalid.

^ Cite error: The named reference AIAA-20190816 was invoked but never defined (see the help page).
^ Cite error: The named reference SA-20200301 was invoked but never defined (see the help page).
^ Krasnikov, S. (2003). "The quantum inequalities do not forbid spacetime shortcuts". Physical Review D. 67 (10): 104013. arXiv:gr-qc/0207057. Bibcode:2003PhRvD..67j4013K. doi:10.1103/PhysRevD.67.104013. S2CID 17498199.
^ Cite error: The named reference Finazzi was invoked but never defined (see the help page).
^ Alcubierre, Miguel (1994). "The warp drive: hyper-fast travel within general relativity". Classical and Quantum Gravity. 11 (5): L73–L77. arXiv:gr-qc/0009013. Bibcode:1994CQGra..11L..73A. doi:10.1088/0264-9381/11/5/001. S2CID 4797900.
^ Thorne, Kip; Michael Morris; Ulvi Yurtsever (1988). "Wormholes, Time Machines, and the Weak Energy Condition" (PDF). Physical Review Letters. 61 (13): 1446–1449. Bibcode:1988PhRvL..61.1446M. doi:10.1103/PhysRevLett.61.1446. PMID 10038800. Archived (PDF) from the original on 23 February 2011.
^ Cramer, John G. (15 April 1996). "The Alcubierre Warp Drive". Archived from the original on 21 September 2012. Alcubierre, following the lead of wormhole theorists, argues that quantum field theory permits the existence of regions of negative energy density under special circumstances, and cites the Casimir effect as an example.

[AIAA-20190816-1] Cite error: The named reference AIAA-20190816 was invoked but never defined (see the help page).

[SA-20200301-2] Cite error: The named reference SA-20200301 was invoked but never defined (see the help page).

[Krasnikov2003-3] Krasnikov, S. (2003). "The quantum inequalities do not forbid spacetime shortcuts". Physical Review D. 67 (10): 104013. arXiv:gr-qc/0207057. Bibcode:2003PhRvD..67j4013K. doi:10.1103/PhysRevD.67.104013. S2CID 17498199.

[Finazzi-4] Cite error: The named reference Finazzi was invoked but never defined (see the help page).

[Alcubierre-5] Alcubierre, Miguel (1994). "The warp drive: hyper-fast travel within general relativity". Classical and Quantum Gravity. 11 (5): L73–L77. arXiv:gr-qc/0009013. Bibcode:1994CQGra..11L..73A. doi:10.1088/0264-9381/11/5/001. S2CID 4797900.

[6] Thorne, Kip; Michael Morris; Ulvi Yurtsever (1988). "Wormholes, Time Machines, and the Weak Energy Condition" (PDF). Physical Review Letters. 61 (13): 1446–1449. Bibcode:1988PhRvL..61.1446M. doi:10.1103/PhysRevLett.61.1446. PMID 10038800. Archived (PDF) from the original on 23 February 2011.

[7] Cramer, John G. (15 April 1996). "The Alcubierre Warp Drive". Archived from the original on 21 September 2012. Alcubierre, following the lead of wormhole theorists, argues that quantum field theory permits the existence of regions of negative energy density under special circumstances, and cites the Casimir effect as an example.

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