Question

All of the discussion so far about relativity has seemed very theoretical and limited to either astrophysics/cosmology. Name at least one part of our modern lives that is completely dependent on precisely and accurately accounting for general relativity. (hint - remember that time runs differently depending on where you are relative to Earth)

Answer 1

General relativity says that the time runs slowly where gravitational field is large. This means at some altitude time runs faster than it does on ground. Hence the time on a GPS satellite clock advances faster than a clock on the ground by roughly 38 microseconds per day.