Question about proper time

Question

A ball is thrown up and falls back down. An astronaut that is circling the Earth at a high speed, and a NASA engineer on Earth both measure the time for this event. Who measures the proper time of this event correctly?

Answer 1

The astronaut,because he has a larger view.

Answer 2

I assume this is a question about the difference in time measurement due to the effects of relativity.

It's a trick question.  BOTH observers measure the "proper time correctly."  In relativity, "proper time" means the time interval as measured in some given reference frame.  The proper time measured by the ground-based observer has one value, and the proper time measured by the astronaut has a different value.  BOTH are correct.  This is because there is NO SUCH THING as an absolute time interval between two events, according to relativity.  There are only relative time intervals as determined in different reference frames.

It's a little like asking, "who measure's the ball's speed correctly?" when the engineer measures it as 13 mph and the astronaut measures it as 1,000 mph.  They're both "correct," because all speed is relative, never absolute.  It's the same way (we now know) when determining the time interval between two events.  Such intervals are relative, never absolute.

Answer 3

the one on earth.

as you go faster, time goes more slowly for you.

there's a famous example of 2 people, one of whom goes on a long space trip, and when he comes back, he's a couple years older, but everyone he knew is long dead.

what that means is that, when he's viewing events taking place on earth, they seem to go by faster for him, because his time is slowed down.

Einstein would probably have kittens at such a simple explanation, but that's as easy as i can make it.

of course, alternatively, one could ask,  "What is proper time?"

and in the context of my answer, it's what we see here on earth.

however, that does not mean that time for the astronaut is "less proper".

it just proceeds at a different pace.