We measure time, I think, by segments of our choosing.
“We measure time, I think, by segments of our choosing.”
Einstein showed that time is not constant, it is relative, and affected by among other things, gravity,.
If you travel at the speed of light for 40 years and then return to earth, you will find that earth will have aged 100,000 years, not 40 years.
So how much time passed in that period?