Expert: Courtney Seligman - 5/5/2009

Question
i saw a show on the science channel hosted by micho kaku and he was on top of a mountain talking about these particles that were coming from space and had some very strange things going on. like the had avery short life span but they still showed up on earth. i cant think of the name of these particles and its driving me crazy. hope you know what im talking about!!thanks for taking questions

Answer
He was probably talking about mu mesons produced by cosmic rays bombarding atoms in our upper atmosphere. Mu mesons 'radioactively' decay into other particles in such a short time that it takes longer than their 'lifetime' to go from the upper atmosphere to the surface of the Earth. As a result, if not for relativistic effects, no mu mesons would reach the surface. But for things, such as mu mesons, which are moving at nearly the speed of light, their 'proper time' seems to stretch out relative to ours, and our 'proper distances' seem to shrink relative to theirs. To us, the mu mesons seem to live longer than usual, because their internal clocks run very slowly. To the mu mesons, the distance from the upper atmosphere to the Earth's surface seems very small. Either way, they make it to the ground, without having decayed along the way.