# Combination of Michelson/Morley and Time Dilation

## Main Question or Discussion Point

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 ?

Related Special and General Relativity News on Phys.org
Dale
Mentor
I feel the pions does not care about the speed of an observer.
That is correct, they do not. In their own frame they decay at the same rate regardless of any observers.

If one observer said, "the pion is traveling 3m/s to the right and 4m/s forward", and if another observer said, "no, the pion is traveling 5m/s forward" would the pions care? Of course not. Would you even say that the observers disagreed? You might, they certainly use different numbers to describe the same thing, but if you asked them a question that was independent of the coordinate system they would always agree.

The point of relativity is just that a time of 1s later is as dependent on the observer as a direction of 1m right.

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 ?
The mean life for such particles do not depend on relativistic effects. However an outside observer's measurement of duration may not agree with the actual lifetime due to relativistic effects.

That is correct, they do not. In their own frame they decay at the same rate regardless of any observers.
Thank you! that's the point.