Regarding “light clocks” and how moving clocks run slow: Does this mean that, if you were on the ISS or some other satellite, clocks on Earth run slow?

Question

I’m still very confused by how clocks could end up out of sync in this way. For example, if you were to send a clock into space, it “runs slow” for awhile, then bring it back to Earth, would it then be permanently “behind” unless it’s manually caught up?

In: Physics

Answer 1

> would it then be permanently “behind” unless it’s manually caught up?

Well you’d have to reset the clock, but just to be clear, it won’t keep running slow once it’s back on Earth. It’s not a problem with the physical clock. The clock is just measuring time, and *time itself* is what’s changing relative to the observer. The astronauts on the ISS age more slowly than people on Earth too, and when they return to the surface they will be some milliseconds younger than they would have been had they not gone up.