Question

To whom does the elapsed time for a process seem to be longer, an observer moving relative to the process or an observer moving with the process? Which observer measures proper time?

a) The observer moving relative to the process; the moving observer measures proper time.

b) The observer moving with the process; the moving observer measures proper time.

c) Both observers measure the same elapsed time.

d) Neither observer measures proper time.

Answer 1

The elapsed time for a process seems longer to an observer moving relative to that process, while an observer moving with the process records the proper time. The observer moving with the process will always measure a shorter time due to the time dilation effect.

Step-by-step explanation:

When considering the elapsed time for a process, it appears differently to observers depending on their relative motion. According to the theory of relativity, the observer moving with the process measures what is known as the proper time, which is the time interval measured by a clock moving with the object in the process. Consequently, the elapsed time for a process seems to be longer for an observer moving relative to the process because of the phenomenon known as time dilation.

So, if an astronaut measures the time it takes for light to reflect within a spaceship, the time she measures (proper time) will be less than the time measured by an observer on Earth, who is not moving with the ship. This is because, from the perspective of the Earth-bound observer, the light has to travel a greater distance as the ship is moving. Since light speed is constant, covering this greater distance requires more time, hence the observed time dilation.

The correct answer to the original question is: b) The observer moving with the process; the moving observer measures proper time.