Philosophy of Physics: A Very Short Introduction (Very Short Introductions)

by David Wallace

Time dilation is a directly observable prediction of relativity. Because the speed of light is so fast, it is most pronounced in the behaviour of sub-atomic particles (the only things we can realistically accelerate to speeds close to light speed). Many of these particles are unstable—they decay into other particles—and they have characteristic decay times, which makes them clocks of a sort. Relativity predicts that these decay times slow down, the faster the particles are moving, and exactly this is observed, both in human-built particle accelerators and in the natural experiments that occur when fast-moving cosmic rays hit the Earth’s atmosphere. The predicted time dilation can be significant—a factor of ten in cosmic-ray experiments, for example—and experiments exactly reproduce those predictions. Large time dilations for massive objects are harder to produce, but modern atomic clocks are so accurate that they can measure even the tiny time dilations caused by putting the clock in an airliner. Again, the experiments reproduce the predictions.

time dilation. interesting explanation.