Editing Michelson–Morley experiment (section)

===Optical tests===
Optical tests of the isotropy of the speed of light became commonplace.<ref group=A >Relativity FAQ (2007): [http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html What is the experimental basis of Special Relativity?]</ref> New technologies, including the use of  [[laser]]s and [[maser]]s, have significantly improved measurement precision. (In the following table, only Essen (1955), Jaseja (1964), and Shamir/Fox (1969) are experiments of Michelson–Morley type, ''i.e.,'' comparing two perpendicular beams. The other optical experiments employed different methods.)

{| class=wikitable
|-
! Author !! Year !! Description !! Upper bounds
|-
| [[Louis Essen]]<ref name=essen />|| 1955 || The frequency of a rotating microwave [[optical cavity|cavity resonator]] is compared with that of a [[quartz clock]] || ~3&nbsp;km/s
|-
| Cedarholm ''et al''.<ref name=cedarholm /><ref name=cedarholm2 />|| 1958 || Two [[ammonia]] masers were mounted on a rotating table, and their beams were directed in opposite directions. || ~30&nbsp;m/s
|-
| [[Ives–Stilwell experiment#Mössbauer rotor experiments|Mössbauer rotor experiments]] || 1960–68 || In a series of experiments by different researchers, the frequencies of [[gamma rays]] were observed using the [[Mössbauer effect]]. || ~2.0&nbsp;cm/s
|-
| Jaseja ''et al''.<ref name=Jaseja />|| 1964 || The frequencies of two [[Helium–neon laser|He–Ne masers]], mounted on a rotating table, were compared. Unlike Cedarholm ''et al.'', the masers were placed perpendicular to each other. || ~30&nbsp;m/s
|-
| nowrap=nowrap| Shamir and Fox<ref name=shamir />|| 1969 || Both arms of the interferometer were contained in a transparent solid ([[Poly(methyl methacrylate)|plexiglass]]). The light source was a [[Helium–neon laser]]. || ~7&nbsp;km/s
|-
| Trimmer ''et al''.<ref name=trimmer /><ref name=trimmer2 />|| 1973 || They searched for anisotropies of the speed of light behaving as the first and third of the [[Legendre polynomials]]. They used a triangle interferometer, with one portion of the path in glass. (In comparison, the Michelson–Morley type experiments test the second Legendre polynomial)<ref name=sexl group=A />|| ~2.5&nbsp;cm/s
|}

[[File:MMX with optical resonators.svg|thumb|250px |Michelson–Morley experiment with cryogenic [[optical resonators]] of a form such as was used by Müller ''et al.'' (2003).<ref name=Muller2003/>]]