Editing Intergalactic travel

{{short description|Hypothetical travel between galaxies}}
'''Intergalactic travel''' is the hypothetical travel between [[galaxy|galaxies]]. Because the [[Milky Way]] and its [[List of nearest galaxies|closest neighbors]] are separated by millions of [[light-year]]s, any such venture would also require millions of years based on our current understanding of physics. Thus, intergalactic travel is impossible within the human lifetime. The technology required to travel between galaxies is far beyond humanity's present capabilities, and currently only the subject of speculation, [[hypothesis]], and [[science fiction]].

==Possible methods==

===Hypervelocity stars===
{{see also|Intergalactic star}}
Theorized in 1988,<ref>{{cite journal
 | first = J. G. | last = Hills | title = Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole | journal = Nature | year = 1988 | volume = 331
 | issue = 6158
 | pages = 687–689 | bibcode = 1988Natur.331..687H
 | doi = 10.1038/331687a0 | s2cid = 4250308 | url = https://zenodo.org/record/1233107 | url-access =  | url-status =  | archive-url =  | archive-date =  }}</ref> and observed in 2005,<ref name='HVS1'>{{cite journal
 | first = Warren R. | last = Brown |author2=Geller, Margaret J. |author3=Kenyon, Scott J. |author4=Kurtz, Michael J.
 | title = Discovery of an Unbound Hypervelocity Star in the Milky Way Halo | journal = Astrophysical Journal | year = 2005
 | volume = 622
 | issue = 1 | pages = L33–L36 | bibcode = 2005ApJ...622L..33B
 | doi = 10.1086/429378 |arxiv = astro-ph/0501177 | s2cid = 14322324 }}</ref> [[hypervelocity stars]] move faster than the [[escape velocity]] of the Milky Way, and are traveling out into intergalactic space.<ref>{{cite news| url=http://hvsproject.blogspot.com/2009/09/hyper-velocity-star-project.html
| title=The Hyper Velocity Star Project: The stars| publisher=The Hyper-Velocity Star Project| date=6 September 2009| access-date=20 September 2014}}</ref> There are several [[Stellar kinematics#Origin of hypervelocity stars|theories for their existence]]. One of the mechanisms would be that the [[supermassive black hole]] at the center of the [[Milky Way]] ejects some stars from the galaxy at a rate of about one every hundred thousand years. Another theorized mechanism might be a supernova explosion in a binary system.<ref>{{cite news
  | url=http://newswise.com/articles/view/535733/
  | title=Chandra discovers cosmic cannonball
  | first=Megan | last=Watzke | date= 28 November 2007
  | publisher=Newswise }}</ref> Intergalactic travel using these stars would involve entering into an orbit around them and waiting for them to reach another galaxy.<ref>{{cite news| url=http://news.discovery.com/space/the-great-escape-intergalactic-travel-is-possible.html| title=The Great Escape: Intergalactic Travel is Possible| author=Villard, Ray| date=24 May 2010| publisher=Discovery News| access-date=October 18, 2010| archive-date=14 November 2012| archive-url=https://web.archive.org/web/20121114090512/http://news.discovery.com/space/the-great-escape-intergalactic-travel-is-possible.html| url-status=dead}}</ref><ref>{{cite news | author= Gilster, Paul | date= 26 June 2014 | url= http://www.centauri-dreams.org/?p=30936 | title= Intergalactic Travel via Hypervelocity Stars | website= centauri-dreams.org | access-date= 16 September 2014}}</ref>

===Time dilation===
While it takes light approximately 2.54 million years to traverse the gulf of space between Earth and, for instance, the [[Andromeda Galaxy]], it would take a much shorter amount of time from the point of view of a traveler at close to the speed of light due to the effects of [[time dilation]]; the time experienced by the traveler depending both on velocity (anything less than the speed of light) and distance traveled ([[length contraction]]). Intergalactic travel for humans is therefore possible, in theory, from the point of view of the traveler.<ref>{{cite news| author=Gilster, Paul| date=25 June 2014| url=http://www.centauri-dreams.org/?p=30929| title=Sagan's Andromeda Crossing| website= centauri-dreams.org | access-date=16 September 2014}}</ref> For example, a rocket that accelerated at [[Standard gravity|standard acceleration due to gravity]] toward the Andromeda Galaxy and started to decelerate halfway through the trip would arrive in about 28 years, from the frame of reference of the observer.<ref>{{cite web|url=http://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html|title=The Relativistic Rocket|website=math.ucr.edu|access-date=4 April 2018}}</ref>

===Superluminal methods===
The [[Alcubierre drive]] is a hypothetical concept that is able to propel a spacecraft to speeds [[faster-than-light|faster than light]] (the spaceship itself would not move faster than light, but the space around it would). This could in theory allow practical intergalactic travel. There is no known way to create the space-distorting wave this concept needs to work, but the metrics of the equations comply with relativity and the limit of light speed.<ref name="Christopher Pike">{{cite journal|author=Alcubierre, Miguel|title=The warp drive: hyper-fast travel within general relativity|journal=[[Classical and Quantum Gravity]] |year=1994|volume=11|pages=L73–L77|doi=10.1088/0264-9381/11/5/001|arxiv = gr-qc/0009013 |bibcode = 1994CQGra..11L..73A|issue=5|s2cid=4797900}}</ref>

A [[wormhole]] is a hypothetical tunnel through space-time that would allow instantaneous intergalactic travel to the most distant galaxies even billions of light years away. Wormholes are allowed by [[general relativity]].<ref>{{cite web |url=https://www.sciencefocus.com/space/wormholes-could-we-travel-through-a-black-hole-into-another-galaxy/ |title=Wormholes: Could we travel through a black hole into another galaxy? |first1=Robert |last1=Matthews |date=20 December 2019 |publisher=Sciencefocus.com |access-date=13 June 2021 }}</ref>

==See also==
{{Portal|Spaceflight
}} 
* Levels of spaceflight: [[Sub-orbital spaceflight|Suborbital]], [[Orbital spaceflight|orbital]], [[Interplanetary spaceflight|interplanetary]], [[Interstellar travel|interstellar]] and intergalactic
* [[Space travel in science fiction]]
* [[Uploaded astronaut]]

==References==
{{Reflist}}

==Notes==
{{notelist}}

{{Space colonization}}
{{Spaceflight| state=collapsed}}

[[Category:Interstellar travel]]
[[Category:Galaxies|-Travel]]
[[Category:Spaceflight]]