Me too. I didn't know that it had been unstuck, but I refer to it more than any single other resource we have.Nugatory said:I think this one is sufficiently important to be a top-level sticky, not just another FAQ entry.
The Michelson-Morley experiment, conducted in 1887, aimed to detect the presence of the "aether," a medium thought to carry light waves. The experiment compared the speed of light in perpendicular directions to detect Earth's motion through the aether. The null result (no difference in light speed) suggested that the speed of light is constant in all directions, contradicting the aether theory and supporting the postulate of Special Relativity that the speed of light is invariant in all inertial frames.
Time dilation, a prediction of Special Relativity, has been confirmed by several experiments. One notable example is the observation of muons created by cosmic rays in the Earth's atmosphere. Muons have a short half-life, but those moving at relativistic speeds reach the Earth's surface in greater numbers than expected because their internal clocks run slower relative to an observer on Earth. This experimental evidence supports the time dilation effect predicted by Special Relativity.
Particle accelerators, such as the Large Hadron Collider, accelerate particles to speeds close to the speed of light. At these high velocities, relativistic effects become significant. The behavior of particles, including their increased mass and the time dilation experienced by unstable particles, aligns with the predictions of Special Relativity. The precise measurements and observations in these accelerators provide strong experimental confirmation of the theory.
The GPS relies on a network of satellites that orbit the Earth and provide precise time and location data. To maintain accuracy, the system must account for relativistic effects, including time dilation due to the satellites' high speeds and gravitational time dilation from their altitude. The necessary adjustments to the satellite clocks, which match the predictions of Special Relativity, demonstrate the practical and experimental validity of the theory in everyday technology.
The Kennedy-Thorndike experiment, conducted in 1932, tested the constancy of the speed of light under different conditions of motion and time. Unlike the Michelson-Morley experiment, it did not rely on the assumption of equal arm lengths in the interferometer. The experiment found no variation in the speed of light with changes in the velocity of the apparatus relative to the supposed aether, further supporting the postulate of Special Relativity that the speed of light is constant in all inertial frames.