The twin paradox seems not to be understand by everybody. But if you see it like this (see below), everybody would understand it. Why are we getting older on Earth ? Our (relative) time system is the system we compare time to the axes of the Earth. If we start in 1 point on the surface (see that point in 3D), we come back there after 24 hours. This must be seen as a negative time dilation in some way, you did not loose time, no you did go faster than time and will be older (my opinion, not going back in time). So time is relative, if you compare it to another point (standing still), this relative time can be used in calculations but not affects age immediately, until you come back in some way to that same point, than you loose/add really extra time to your existence. In case of a muon, this can also be explained as a calculation with time, not the "age" of a muon. Could this all be right ?