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In [[General relativity]], the '''Shapiro effect''', or '''gravitational time delay''', is one of the four classic [[solar system tests]] of general relativity. It says that a [[radar]] beam (or [[light beam]]) which passes near a massive object as it travels from some observer's ___location to a target and returns to the observer, takes slightly longer to make the round trip (as measured by the observer) than it would if the object were not present.
===[[Borrowdale dance]]===
More generally, the "travel time" of any signal moving at the '''local speed of light''' can be affected by the gravitational field in regions of spacetime through which it travels. In general relativity (and in most other gravitation theories), the local speed of light is a constant of nature, but the time delay effect implies that the effective '''global speed of light''' is [[path-dependent]].
I dont even know what this is but it only has 87 unique google hits so its probaly nn '''Delete'''--[[User:Aranda56|JAranda]]'' | [[User talk:Aranda56|watz sup]] 21:42, 12 November 2005 (UTC)
The time delay effect was first noticed in 1964, by [[Irwin I. Shapiro]]. Shapiro proposed an observational test of his prediction: bounce radar beams off the surface of Venus and Mercury, and measure the round trip travel time. When the Earth, Sun, and Venus are most favorably aligned, Shapiro showed that the expected time delay, due to the presence of the Sun, of a radar signal traveling from the Earth to Venus and back, would be about 200 milliseconds, well within the limitations of 1960s era technology.
* '''Weak keep''' Given the scarcity of Web material about Zimbabwe I'd keep this as it's verifiable although somewhat localised see e.g. [http://64.233.183.104/search?q=cache:B5etkc0E8ugJ:www.delta.co.zw/home.cfm%3Fpg_id%3D69%26lnk_id%3D7+Borrowdale+dance&hl=en] [[User:Dlyons493|<FONT COLOR="#00FF00">Dl</FONT><FONT COLOR="#44FF00">yo</FONT><FONT COLOR="#99DD11">ns</FONT><FONT COLOR="#DDDD11">493</FONT>]] [[User_talk:Dlyons493|<FONT COLOR="#DDDD11">Ta</FONT><FONT COLOR="#00FF00">lk</FONT>]] 22:46, 12 November 2005 (UTC)
*'''Keep''' and expand. It seems to be associated with musician [[Alick Macheso]] who also has the nickname of Borrowdale see [http://66.102.7.104/search?q=cache:UvPEMljArvkJ:www.herald.co.zw/index.php%3Fid%3D37415%26pubdate%3D2004-11-04+%22Borrowdale+dance%22&hl=en&lr=lang_en].
The first test, using the [[Massachusetts Institute of Technology|MIT]] [[Haystack radar antenna]], was successful, matching the predicted amount of time delay. The experiments have been repeated many times since, with increasing accuracy.
. [[User:Capitalistroadster|Capitalistroadster]] 00:38, 13 November 2005 (UTC)
*'''Keep'''. It looks to be real, and notable in Zimbabwe. - [[User:Dalbury|Dalbury]] [[User_talk:Dalbury|(talk)]] 02:09, 13 November 2005 (UTC)
==References==
*'''Keep''' Looks to be notable in Zimbabwe. [[User:Denni|D]][[Wikipedia:Esperanza|<font style="color:green">'''''e'''''</font>]][[User:Denni|nni]][[User_talk:Denni|<font color=#228822>☯</font>]] 00:21, 14 November 2005 (UTC)
* {{Journal reference | Author=Irwin I. Shapiro | Title=Fourth Test of General Relativity | Journal=Physical Review Letters | Year=December 1964 | Volume=13 | Pages=789-791}}
* {{Journal reference | Author=Irwin I. Shapiro, Gordon H. Pettengill, Michael E. Ash, Melvin L. Stone, William B. Smith, Richard P. Ingalls, and Richard A. Brockelman | Title=Fourth Test of General Relativity: Preliminary Results | Journal=Physical Review Letters | Year=May 1968 | Volume=20 | Pages=1265–1269}}
* {{Book reference | Author=d'Inverno, Ray | Title=Introducing Einstein's Relativity | Publisher=Oxford: Clarendon Press | Year=1992 | ID=ISBN 0-19-859686-3}} See '''Section 15.6''' for an excellent advanced undergraduate level introduction to the Shapiro effect.
* {{Journal reference | Author=Will, Clifford M. | Title=The Confrontation between General Relativity and Experiment | Journal=Living Rev. Rel. | Year= 2001 | Volume=4 | Pages=4-107}} See also [http://arxiv.org/abs/gr-qc/0103044 gr-qc/0103044] A graduate level survey of the solar system tests, and more.
[[Category:Tests of general relativity]]
[[Category:Effects of gravity]]
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