Speed of light is only possible to verify experimentally that the two-way speed of light (for example, from a source to a mirror and back again) is frame-independent, because it is impossible to measure the one-way speed of light (for example, from a source to a distant detector) without some convention as to how clocks at the source and at the detector should be synchronized. However, by adopting Einstein synchronization for the clocks, the one-way speed of light becomes equal to the two-way speed of light by definition. The special theory of relativity explores the consequences of this invariance of "c" with the
One-way speed of light that slow clock-transport, the laws of motion, and the way inertial reference frames are defined, already involve the assumption of isotropic one-way speeds and thus are conventional as well. In general, it was shown that these experiments are consistent with anisotropic one-way light speed as long as the two-way light speed is isotropic. The 'speed of light' in this article refers to the speed of all electromagnetic radiation in vacuum. The two-way speed of light is the average speed of light from one point, such as a source, to a mirror and back again. Because the light starts and finishes