Editing Fifth force (section)

===Equivalence principle===
One way to search for a fifth force is with tests of the strong [[equivalence principle]], one of the most powerful tests of [[general relativity]], also known as Einstein's theory of gravity. Alternative theories of gravity, such as [[Brans–Dicke theory]], postulate a fifth {{nowrap|force{{tsp}}{{mdash}}}}{{tsp}}possibly one with infinite range. This is because gravitational interactions, in theories other than general relativity, have [[degrees of freedom (physics and chemistry)|degrees of freedom]] other than the [[metric tensor|"metric"]], which dictates the [[curvature]] of space, and different kinds of degrees of freedom produce different effects. For example, a [[scalar field]] cannot produce the [[bending of starlight|bending of light rays]].

The fifth force would manifest itself in an effect on solar system orbits, called the [[Nordtvedt effect]]. This is tested with [[Lunar Laser Ranging experiment]]<ref>{{cite web |title=Lunar laser ranging |url=http://funphysics.jpl.nasa.gov/technical/grp/lunar-laser.html |access-date=2005-05-07 |url-status=dead |archive-url=https://web.archive.org/web/20161128185551/http://funphysics.jpl.nasa.gov/technical/grp/lunar-laser.html |archive-date=2016-11-28 |df=dmy-all}}</ref> and [[very-long-baseline interferometry]].