The first direct experimental confirmation of the second postulate of special relativity (the constancy of the speed of light) have implemented physics at the Kurchatov center of synchrotron radiation. The work was done under the guidance of Academician Evgeny Alexandrov.
In the experiments, the pulsed light source was a source of synchrotron radiation (SR) — electron storage ring Siberia-1 at the Kurchatov Synchrotron Radiation Research Center, EC.
Attempts to test the postulate began 60 years ago when the academician Vavilov had his doctorate AM Bonch-an experiment. Vavilov proposed to his student to design the unit in which the light source was a beam of fast excited atoms. In the course of detailed work plan of the experiment it was found that there is no chance to get a reliable result, since the technology of the day could not be relied on bundles the necessary speed and density: the expected under the hypothesis of ballistic correction to the speed of light was provided at the level of interest and the intensity of the radiation beam was estimated too low. The experience was not implemented.
Over the past few decades, various attempts to prove experimentally the second postulate stations repeatedly been made by scientists. All the authors of these works have come to the conclusion on the validity of the postulate.
But it did not stop the critical speeches in which to raise objections against the ideas of experiments or questioned their accuracy. The latter is connected, usually with small attainable velocity of the radiation source relative to the speed of light.
Now the Russian physicists were able to realize the experiment proposed by Vavilov, the original beauty, because physics is today in the hands of an extremely bright ultra-relativistic source. This synchrotron emitter, wherein the light source is a bundle of electrons moving along a curved trajectory at a speed very close to the speed of light.
Installation and layout of the experiment / / E.B.Aleksandrov, P.A.Aleksandrov, V.S.Zapassky etc., UFN 181, № 12 (2011)
In these conditions it is easy to measure the speed of light emitted in a perfect laboratory vacuum. By the logic of ballistic hypothesis, this rate should be equal to twice the speed of light from a stationary source. This is a very rough effect, the discovery of which (if it exists) would not need any special tricks. Indeed, it is enough to simply measure the passage of light pulse dimensional segment in an evacuated space.
The results of measurements, which can be found here, reiterated the commitment of the postulate. Thus, it was first performed a direct measurement of the speed of light emitted ultrarelativistic source.
"You could say that this is a demonstration experiment for future textbooks of physics." — Said Alexander. — "Of course, for professional physicists, there is no doubt in the expected result. In this sense, the experience is useless. However, a direct demonstration of the constancy of the speed of light is of great didactic value, limiting the way for further speculation about the absence of proof of the foundations of the theory of relativity. Physics in its development ever came back to play and refinement of fundamental experiments carried out with the new technical possibilities. In this case the aim is to clarify the speed of light. It is about filling gaps in the historical origins of experimental substantiation stations, which should facilitate the perception of this rather paradoxical theory. "