Hi, I found myself trapped in a question on Special Relativity for 15 years now. Because of other new theories (LQG) the question became actual for me again. Maybe some of you can give me anwer on it: Is the combination of the experiments "Michelson and Morley experiment" and "Time Dilation" is testing something different, or is it just the same ? 1. The Michelson and Morley experiment intended to measure the velocity of the Earth relative to the “lumeniferous æther”. It failed, because SR prediction of Light-Speed Isotropy was correct. 2. Time Dilation experiments showed that particle lifetimes are showing relativistic time dilation. As far as I know, the limited lifetime of e.g. mesons is caused by the weak interaction, a fundamental force. The mean life is depending on the relativic effects caused by the high speed. If the decay process is obeserved by a different inertial system, does the expectation of the mean life follow the Special Relativity ? For illustration, please imagine the following new experiment: - We create a lot of pions with a particle accelerator. - We measure the direction and decay of the pions in space (according to current direction of earth). - we do not measure the velocity I feel the pions does not care about the speed of an observer. The EPR paradox on Quantum entanglement showed that Relativity can still be unaffected on larger scales, if it is not based on information exchange. Does the direction of the pions has no measureable effect on the mean life ?