Editing Roman ring

{{short description|Configuration of wormholes}}
{{About|the physics concept|the gymnastics apparatus|Rings (gymnastics)}}

In [[general relativity]], a '''Roman ring''' (proposed by [[Matt Visser]] in 1997<ref>{{cite journal | author=Visser, Matt| title= Traversable wormholes: the Roman ring | arxiv=gr-qc/9702043 | doi=10.1103/PhysRevD.55.5212 | volume=55 | journal=Physical Review D | year= 1997 | issue= 8 | pages=5212–5214| bibcode=1997PhRvD..55.5212V| s2cid= 2869291 }}</ref> and named after the '''Roman arch'''<!--boldface per WP:R#PLA-->, a concept proposed by [[Mike Morris (physicist)|Mike Morris]] and [[Kip Thorne]] in 1988 and named after physicist [[Tom Roman]])<ref>{{cite journal | author = Morris M. S., Thorne K. S. | year = 1988 | title = Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity | url = https://archive.org/details/pdfy--5NLGQyfpB61dmyG | journal = Am. J. Phys. | volume = 56 | issue = 5 | page = 395 | doi=10.1119/1.15620| bibcode = 1988AmJPh..56..395M | doi-access = free }}</ref> is a configuration of [[wormhole]]s where no subset of wormholes is near to [[chronology violation]], though the combined system can be arbitrarily close to chronology violation.

==Examples==
For example, an [[Earth]]–[[Moon]] wormhole whose far end is 0.5 seconds in the "[[Relativity of simultaneity|past]]" will not violate [[causality]], since [[information]] sent to the far end via the wormhole and back through normal space will still arrive back on Earth (-0.5 + 1) = 0.5 seconds after it was transmitted; but an additional wormhole in the other direction will allow information to arrive back on Earth 1 second ''before'' it was transmitted (time travel). However, it is believed that relative time between the transmission of the information in one wormhole throat and out of the other end in a ring structure will remain the same, because light wouldn't have violated local proper time, because the distance traveled by the information would take time, either by going the long way or through the wormhole.

==Chronology protection==
[[Semiclassical gravity|Semiclassical]] approaches to incorporating quantum effects into general relativity seem to show that the [[chronology protection conjecture]] postulated by physicist [[Stephen Hawking]] fails to prevent the formation of such rings, although [[Matt Visser]] feels that there are reasons to think the semiclassical approach is unreliable here, and that a full theory of [[quantum gravity]] will likely uphold chronology protection.

==Gallery==
[[Image:Roman ring with one wormhole.png|frame|left|A wormhole with no [[Closed timelike curves]] (CTC)]]
[[Image:Roman ring with two wormholes.png|frame|left|A Roman ring with two wormholes]]
[[Image:Roman ring with four wormholes.png|frame|left|A Roman ring with four wormholes]]
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==Notes==
{{reflist}}

== References ==
* {{cite journal| author=Visser, Matt| title= van Vleck determinants: traversable wormhole spacetimes | arxiv=gr-qc/9311026 | doi=10.1103/PhysRevD.49.3963| volume=49| journal=Physical Review D| year= 1994 | issue= 8 | pages=3963–3980| pmid= 10017400 | bibcode=1994PhRvD..49.3963V| s2cid= 38145051 }}

[[Category:General relativity]]
[[Category:Time travel]]
[[Category:Wormhole theory]]


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