The rest frame lifetime of a muon is 2.2 microseconds. Muons are produced in the upper atmosphere by collisions with cosmic rays. The light travel time from the upper atmosphere to the ground is about 150 microseconds. Nevertheless, a substantial fraction of muons produced in the upper atmosphere are observed on the ground. For an observer on the ground, which of the following principles best explains this phenomenon?

W) Length contraction

X) Atmospheric scintillation

Y) Time dilation

Z) Pair production
Y) TIME DILATION