Time Dilation and Length Contraction - The Evidence

1. Time Dilation and Length Contraction - The Evidence Know how muons are produced in the upper atmosphere Be able to explain the evidence from Rossi’s experiment regarding muon decay Calculate the intensity of muons arriving at the Erath’s surface by allowing for time dilation

2. Collecting muons 2000m

3. What is a muon and where and how are they produced ? • Muons are created when the cosmic 'wind' interacts with the upper atmosphere and when this happens they travel at a speed of 0.996c • Muons are radioactive particles which decay to form either a electron or a positron together with a neutrino and an anti-neutrino • Low energy muons have a half life of around 1.5μs at rest. • When we make observations concerning muons moving at this speed there are two frames of reference that are important.

4. True or False • In the muon's frame, its lifetime on its own clock is 1.5μs • True • The speed of light is different in the two frames of reference. • False • An observer in the muon's frame observes that the muon's clock is running slow. • False • The laboratory observer observes that the muons travel a shorter distance in the laboratory than light could travel in a muon's rest lifetime. • False • The laboratory observer reckons that the muon's clock is running fast compared to her own. • False • The moving muon's lifetime as measured by the laboratory observer is longer than when the muon is at rest. • True • Moving clocks run slow when compared to stationary clocks. • True • In the muon's frame, the depth of the atmosphere is less than the laboratory observer measures it to be in her own frame. • True