Built of Facts: A Brief History of Light
A nit (nit being the quanta of disagreement or concern):
Water waves and sound waves need something material to “wave”. Physicists assumed there was a thin and invisible medium called luminiferous aether permeating the universe, and that light waves were oscillations of this substance. But in 1887, Albert Michelson and Edward Morley were able to do a very careful experiment to measure the speed of light as the earth moved through the aether as it orbited in space. Their experiment came up negative. There just wasn’t any aether.
M&M were attempting to ultimately confirm the speed of the earth moving through the ether, via changes in the speed of light, and the reason they knew they had to do this measurement is that way back in 1725, James Bradley had measured stellar aberration — the apparent shift in position of a star due to the motion of the earth, which manifests itself in measurements taken at different times of the year. If the earth were somehow at rest with respect to the ether, there should be no aberration, so this option was already eliminated when the models of electromagnetic wave propagation were being hammered out. The M-M experiment was the experiment that showed we weren’t moving with respect to it, because being at rest wasn’t an option for explaining the null result.
The Michelson-Morley experiment showed space is isotropic to massless photons to differential 10^(-8) relative in 1887. A 2007 study sensitive to 10^(-16) employed two simultaneous interferometers over a year’s observation: Optical in Berlin, Germany at 52°31’N 13°20’E and microwave in Perth, Australia at 31°53’S 115°53E. An aether background could never be at rest relative to both of them all year.
http://arXiv.org/abs/0706.2031
Nobody knows if space is isotropic to metaphorc opposite shoes: 24 hours of microwave spectrometry of rigidly connected left-left, left-right, and right-right vacuum phase paired propellers at 45 latitude. If the vacuum is anisotropic to chiral mass (sorry, photons), the homochiral rotation spectra will diurnally diverge from that of the meso-rotor.
http://www.mazepath.com/uncleal/twisten3.gif
Somebody should look.