Editing Interstellar travel (section)

==== Faster-than-light travel ====
[[File:Wormhole travel as envisioned by Les Bossinas for NASA.jpg|thumb|Artist's depiction of a hypothetical ''Wormhole Induction Propelled Spacecraft'', based loosely on the 1994 "[[Alcubierre drive|warp drive]]" paper of [[Miguel Alcubierre]]]]
{{Main|Faster-than-light}}

Scientists and authors have postulated a number of ways by which it might be possible to surpass the speed of light, but even the most serious-minded of these are highly speculative.<ref name="crawftl">{{cite journal|last1=Crawford|first1=Ian A.|title=Some thoughts on the implications of faster-than-light interstellar space travel|journal=Quarterly Journal of the Royal Astronomical Society|date=1995|volume=36|pages=205–218|bibcode=1995QJRAS..36..205C}}</ref>

It is also debatable whether faster-than-light travel is physically possible, in part because of [[Tachyonic antitelephone|causality]] concerns: travel faster than light may, under certain conditions, permit travel backwards in time within the context of [[special relativity]].<ref>{{cite journal|last1=Feinberg|first1=G.|title=Possibility of faster-than-light particles|journal=Physical Review|date=1967|volume=159|issue=5|pages=1089–1105|doi=10.1103/physrev.159.1089|bibcode = 1967PhRv..159.1089F }}</ref> Proposed mechanisms for [[faster-than-light]] travel within the theory of general relativity require the existence of [[exotic matter]]<ref name="crawftl" /> and, it is not known if it could be produced in sufficient quantities, if at all.

===== Alcubierre drive =====

{{Main|Alcubierre drive}}
In physics, the [[Alcubierre drive]] is based on an argument, within the framework of [[general relativity]] and without the introduction of [[wormhole]]s, that it is possible to modify spacetime in a way that allows a spaceship to travel with an arbitrarily large speed by a local expansion of spacetime behind the spaceship and an opposite contraction in front of it.<ref name="Warp Alcubierre">{{cite journal |title=The warp drive: hyper-fast travel within general relativity |journal=Classical and Quantum Gravity |year=1994 |last=Alcubierre |first=Miguel |volume=11 |issue=5 |doi=10.1088/0264-9381/11/5/001 |pages=L73–L77|arxiv = gr-qc/0009013 |bibcode = 1994CQGra..11L..73A |citeseerx=10.1.1.338.8690 |s2cid=4797900 }}</ref> Nevertheless, this concept would require the spaceship to incorporate a region of [[exotic matter]], or the hypothetical concept of [[negative mass]].<ref name="Warp Alcubierre" />

===== Wormholes =====
[[Wormhole]]s are conjectural distortions in spacetime that theorists postulate could connect two arbitrary points in the universe, across an [[Einstein–Rosen Bridge]]. It is not known whether wormholes are possible in practice. Although there are solutions to the Einstein equation of general relativity that allow for wormholes, all of the currently known solutions involve some assumption, for example the existence of [[negative mass]], which may be unphysical.<ref>{{cite web |url=http://www.nasa.gov/centers/glenn/technology/warp/ideachev.html#worm |title=Ideas Based On What We'd Like To Achieve: Worm Hole transportation |date=11 March 2015 |publisher=NASA Glenn Research Center |access-date=4 September 2012 |archive-date=24 September 2013 |archive-url=https://web.archive.org/web/20130924060726/http://www.nasa.gov/centers/glenn/technology/warp/ideachev.html#worm |url-status=live }}</ref> However, Cramer ''et al.'' argue that such wormholes might have been created in the early universe, stabilized by [[cosmic string]]s.<ref>{{cite journal | author= John G. Cramer| author2= Robert L. Forward| author3= Michael S. Morris| author4= Matt Visser| author5= Gregory Benford| author6= Geoffrey A. Landis | title= Natural Wormholes as Gravitational Lenses | journal= Physical Review D | volume= 51 | issue= 3117 | date= 15 March 1995 | pages= 3117–3120 | doi= 10.1103/PhysRevD.51.3117 | pmid= 10018782| arxiv= ph/9409051|bibcode = 1995PhRvD..51.3117C | s2cid= 42837620}}</ref> The general theory of wormholes is discussed by Visser in the book ''Lorentzian Wormholes''.<ref>{{cite book | author= Visser, M. | date= 1995 | title= Lorentzian Wormholes: from Einstein to Hawking | publisher= AIP Press, Woodbury NY | isbn= 978-1-56396-394-0}}</ref>