Cosmic Ray Muons are an experimental verification of Special Relativity.
Muons are produced in the upper atompshere in colluision betweren ultra high energy cosmic ray particles and air molecule nuclei. But they decay (lifetime = 1.52 ) on their way to the earth’s surface, with an average velocity of 98% of the Speed of Light. Because they are travelling so fast Relativistic Effects are measureable due to the fact that they penetrate the atmosphere deeper than classical physics would predict. Without Time Dilation, we expect 45 muons in theory. The experiment shows 542 muons which agrees with the prediction of 538 by Special Relativity. From the perspective of the muon, the earth is moving with a speed of .98c. It will see the distance it travels as a Length Contraction. Thus, in both reference frames the result is the same. In one reference frame, time dilates, and in the other length contracts.