The experimental confirmation of the invariance of the speed of light comes from a variety of sources and has been repeatedly verified through different experiments. Here are a few key experiments that provide evidence for the constancy of the speed of light:
Michelson-Morley Experiment (1887): This famous experiment was designed to detect the hypothetical "ether" medium through which light was thought to propagate. The experiment involved splitting a beam of light and sending the two beams in different perpendicular directions before recombining them. The interference pattern formed by the recombined beams was expected to shift due to the motion of the Earth through the stationary ether. However, the experiment consistently yielded null results, indicating that the speed of light is the same in all directions and that there is no preferred reference frame.
Ives-Stilwell Experiment (1938): This experiment involved measuring the shift in the frequency of light emitted by moving atoms. The experimenters observed that when fast-moving atoms emitted light, the frequency of the emitted light appeared to be shifted, indicating time dilation effects predicted by special relativity. The results confirmed that the speed of light is invariant regardless of the relative motion between the source and the observer.
Lunar Laser Ranging Experiment: This ongoing experiment involves bouncing laser beams off retroreflectors placed on the Moon by Apollo astronauts. By precisely measuring the time it takes for the laser beams to travel to the Moon and back, scientists can determine the distance between the Earth and the Moon with great accuracy. The consistency of these measurements over time supports the invariance of the speed of light.
Particle Accelerator Experiments: Particle accelerators, such as the Large Hadron Collider (LHC), accelerate particles to near-light speeds. The behavior of these particles, as observed in the experiments, aligns with the predictions of special relativity, including time dilation and length contraction. The fact that these relativistic effects are observed in particle collisions supports the constancy of the speed of light.
These are just a few examples of the numerous experiments conducted over the years that provide strong evidence for the invariance of the speed of light. The consistency of the results across different experiments and their agreement with the predictions of relativity theory supports the fundamental nature of the speed of light as a universal constant.