If I was going the speed of light and travelled 10 light years, would that be 10 years to someone on earth or 10 years to me?
Suppose a child goes into space (in spacecraft) at the speed of light and another child (identical in all respects with the 1st child) lives on Earth. Now, if the 2nd child living on Earth meets the 1st child after 10 years on Earth, what will be the age difference between the two?