# Time and GPS Satellites

*Most recent answer: 01/03/2020*

- Santhosh Mohan (age 27)

Chennai

The phrase "at any point in time" already refers to something that we've found does not exist in our universe. Whiichevents of the different satellites are simultaneous, i.e. at the same point in time, *depends on the observer*.

As for the different rates of different closcks, there are two effects. One is that for clocks in motion relative to each other, an oberver on either clock sees the other one as going slow. The other is that in the presence of gravitational fields or accelerations, there are observer-independent differences in the rate of the clocks. The net effect is that one each orbit the clocks on the GPS satellites have advanced more than a clock on earth. Any effects due to signal transmission times can be made comparatively negligible just by allowing many orbits for the other effect to accumulate. For lower-orbit satellites, it turns out the net effect is opposite, so that they advance more slowly than a clock on earth.

I'm not sure that answered your questio, so you might want o follow up.

Mike W.

*(published on 01/03/2020)*