# Gravity and time

1. Jan 18, 2010

### Mr Peanut

Say I'm near the earth and traveling at 17000 mile per hour. Relative to my local time, is it earlier or later on earth? Or is it the same time?

2. Jan 18, 2010

### tiny-tim

Hi Mr Peanut!

("earlier" or "later" is irrelevant ; the question is whether clocks are slower or faster)

Special relativity says that you measure an Earth clock as going slow, and we on Earth measure your clock as going equally slow.

General relativity adds that, whatever your speed, your clock will be slightly faster than it would otherwise be, because of the weaker gravity where you are.

3. Jan 18, 2010

### GRDixon

According to SRT your satellite onboard clock will run more slowly than an earthbound clock. I believe that this slowing down exceeds the difference in clock rates attributable to the earthbound clock's location deeper in the Earth's gravitational field. This being the case, the net result would be that the satellite clock gradually loses time compared to the earthbound clock. I think that this may have been experimentally verified. Dr. Neil Ashby, University of Colorado, would be an authority. He has done extensive GRT analysis for the Global Positioning folks.