please read this problem(adsbygoogle = window.adsbygoogle || []).push({});

"An astronaut traveling in a spaceship aims his flashlight to an object inside the spaceship, the beam of light moves on the same direction as the direction of motion of the ship, he observed the time interval between the light leaves the flashlight and when it hits the object, another observer on the earth measure the time interval between the two events, which one of them measures the proper time interval between these two events?"

i thought that the answer of this question is that the first observer measures the proper time

but the answer was "neither of them measures the proper time"

i need to know why?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Proper time problem

**Physics Forums | Science Articles, Homework Help, Discussion**