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source for cosmic string spacetime as "Euclidean geometry with a slice taken out whose edges are identified to turn the geometry into a cone" |
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==Gravitation==
{{refimprove section|date=September 2016}}
A string is a geometrical deviation from [[Euclidean geometry]] in spacetime characterized by an angular deficit: a circle around the outside of a string would comprise a total angle less than 360°. <ref>{{cite journal| last=Gott| first=J. Richard| title=Closed timelike curves produced by pairs of moving cosmic strings: Exact solutions| journal=Phys. Rev. Lett.| date=1991| volume=66| issue=9| page=1126| doi=10.1103/PhysRevLett.66.1126}}</ref> From the [[general theory of relativity]] such a geometrical defect must be in tension, and would be manifested by mass. Even though cosmic strings are thought to be extremely thin, they would have immense density, and so would represent significant gravitational wave sources. A cosmic string about a kilometer in length may be more massive than the Earth.
However [[general relativity]] predicts that the gravitational potential of a straight string vanishes: there is no gravitational force on static surrounding matter. The only gravitational effect of a straight cosmic string is a relative deflection of matter (or light) passing the string on opposite sides (a purely topological effect). A closed cosmic string gravitates in a more conventional way.{{clarify|date=September 2019}}
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