Editing Alcubierre drive (section)

==Alcubierre metric==
The Alcubierre [[metric tensor|metric]] defines the warp-drive [[spacetime]]. It is a [[Lorentzian manifold]] that, if interpreted in the context of [[general relativity]], allows a warp bubble to appear in previously flat spacetime and move away at effectively faster-than-light speed. The interior of the bubble is an [[inertial reference frame]] and inhabitants experience no proper acceleration. This method of transport does not involve objects in motion at faster-than-light speeds with respect to the contents of the warp bubble; that is, a light beam within the warp bubble would still always move more quickly than the ship. Because objects within the bubble are not moving (locally) more quickly than light, the mathematical formulation of the Alcubierre metric is consistent with the conventional claims of the laws of relativity (namely, that an object with mass cannot attain or exceed the speed of light) and conventional [[special relativity|relativistic]] effects such as [[time dilation]] would not apply as they would with conventional motion at near-light speeds.<ref name=":3">{{cite book |last1=Alcubierre |first1=Miguel |date=2017 |pages=257–279 |place=Cham |isbn=978-3-319-55181-4 |last2=Lobo |first2=Francisco S. N.|title=Wormholes, Warp Drives and Energy Conditions |chapter=Warp Drive Basics |series=Fundamental Theories of Physics |volume=189 |doi=10.1007/978-3-319-55182-1_11 |arxiv=2103.05610 |bibcode=2017FTP...189..257A }}</ref>

An extension of the Alcubierre metric that eliminates the expansion of the volume elements and instead relies on the change in distances along the direction of travel is that of mathematician José Natário. In his metric, spacetime contracts towards the prow of the ship and expands in the direction perpendicular to the motion, meaning that the bubble actually "slides" through space, roughly speaking by "pushing space aside".<ref name=":3" /><ref>{{Cite book |last1=Everett |first1=Allen |title=Time Travel and Warp Drives |last2=Roman |first2=Thomas |date=2011 |publisher=University of Chicago Press |doi=10.7208/chicago/9780226225005.001.0001 |isbn=978-0-226-04548-1}}</ref>

The Alcubierre drive remains a hypothetical concept with seemingly difficult problems, although the amount of energy required is no longer thought to be unobtainably large.<ref name="WDmorefeasible">{{Cite web |last=Moskowitz |first=Clara |date=17 September 2012 |title=Warp Drive May Be More Feasible Than Thought, Scientists Say |url=http://www.space.com/17628-warp-drive-possible-interstellar-spaceflight.html |url-status=live |archive-url=https://web.archive.org/web/20130113193555/http://www.space.com/17628-warp-drive-possible-interstellar-spaceflight.html |archive-date=13 January 2013 |publisher=[[Space.com]]}}</ref> However, Alexey Bobrick and Gianni Martire claim that, in principle, a class of subluminal, spherically symmetric warp drive spacetimes can be constructed based on physical principles presently known to humanity, such as positive energy.<ref>{{Cite journal |last1=Bobrick |first1=Alexey |last2=Martire |first2=Gianni |date=2021-04-20 |title=Introducing physical warp drives |url=https://iopscience.iop.org/article/10.1088/1361-6382/abdf6e |journal=Classical and Quantum Gravity |volume=38 |issue=10 |pages=105009 |arxiv=2102.06824 |bibcode=2021CQGra..38j5009B |doi=10.1088/1361-6382/abdf6e |issn=0264-9381 |s2cid=231924903}}</ref> Furthermore, a study by Remo Garattini and Kirill Zatrimaylov shows that the amount of negative energy density required to sustain a warp bubble can in principle be reduced if the bubble is moving in an external gravitational field, such as that of a black hole.<ref>{{Cite journal |last1=Garattini |first1=Remo |last2=Zatrimaylov |first2=Kirill |date=2024-07-29 |title=Black Holes, Warp Drives, and Energy Conditions |url=https://www.sciencedirect.com/science/article/pii/S0370269324004684 |journal=Physics Letters B |volume=856 |arxiv=2408.04495 |bibcode=2024PhLB..85638910G |doi=10.1016/j.physletb.2024.138910|issn=0370-2693|s2cid=271554785}}</ref><ref>{{Cite news|url=https://www.sciencealert.com/what-would-happen-if-a-warp-drive-spaceship-flew-into-a-black-hole|title=What Would Happen if a Warp Drive Spaceship Flew Into a Black Hole?|first=Carolyn|last=Collins Petersen|work=Universe Today|via=ScienceAlert}}</ref>