If we launch a spaceship at relativistic speeds, the time on the spaceship, compared with Earth's, will pass slower. After a year on the spaceship, on Earth could have passed several years. And, if the spaceship reaches the speed of light, it would appear stopped in time from Earth's perspective. Assuming we could measure it.
On GPS satellites, the inverse happens. They are further away from Earth's gravitational pool than an observer on Earth, so there is a time dilation of 45.9 μs/day. If we could 'see' inside the satellite, everything on it would be moving slightly faster.
I am interested about the second case. What is the greatest difference on time dilation (on the 'faster if seen from Earth' side) that an object can have, with an observer on Earth as reference?
My guess is that it would be something completely removed from any gravity pool and without speed. My first guess was that 'whithout speed' means that it should be idle on the middle of the void, but speed and time dilation without a reference doesn't make sense. So the object should be 'idle' compared to Earth, moving at the same speed than the planet. Correct me if I am wrong, please.
