Time and Gravity Stopping

[syntax252]

Happens all the time, though, if you use GPS.

 

As I understand GPS, the clocks in the units are constantly reset from atomic clocks in the satellites in order that they might be able to know the exact position of the satellite, not because of any difference in how fast time passes between the two.

 

Am I wrong about that?

[Sayonara]

No.

 

And if by papers you mean newspapers, they're not really the best source.

[swansont]

As I understand GPS' date=' the clocks in the units are constantly reset from atomic clocks in the satellites in order that they might be able to know the exact position of the satellite, not because of any difference in how fast time passes between the two.

 

Am I wrong about that? [/quote']

 

The synchronization of GPS satellite clocks ocurs for a variety of reasons - no two clocks can stay in synch anyway, for one, and deviation from perfect orbits, and other reasons.

 

Clocks in the satellites run at different rates than the ground clocks. The basic difference is hard-wired in so that the time you get from reading the satellites is correct when you read it on the ground.

[syntax252]

The synchronization of GPS satellite clocks ocurs for a variety of reasons - no two clocks can stay in synch anyway' date=' for one, and deviation from perfect orbits, and other reasons.

 

Clocks in the satellites run at different rates than the ground clocks. The basic difference is hard-wired in so that the time you get from reading the satellites is correct when you read it on the ground.[/quote']

 

Just to be clear. You are saying that time passes more rapidly on a sattellite than it does on the ground?

[swansont]

Just to be clear. You are saying that time passes more rapidly on a sattellite than it does on the ground?

 

For GPS satellites, yes. The kinetic time dilation term is smaller than the decrease in the gravitational term. In LEO, like for the shuttle or ISS, the kinetic term is bigger.

[syntax252]

For GPS satellites, yes. The kinetic time dilation term is smaller than the decrease in the gravitational term. In LEO, like for the shuttle or ISS, the kinetic term is bigger.

 

 

Well would time pass faster on the moon? it is also a satellitte of the Earth. And how much faster would time pass on the moon?

[calbiterol]

It's all about general and special relativity... Like, if you've ever ready any of the books from the Ender's Game series by Orson Scott Card, you'd remember that time passes slowly for bodies of mass that approach the speed of light, while everything outside of that body of mass remains at its norm. It's the same principle with the satellites, and the moon. The faster an opject is travelling, the greater the effect of time dilation, and the slower time passes for that object. It's just to a much smaller degree. The clocks in the satellites are very, very precise, as they need to be. So in order to be (nearly) perfectly in sync, they must synchronize.

 

I believe gravity has a similar effect on time through a process called frame dragging. If you want some more detailed information, look up NASA's Gravity Probe B.

[swansont]

Well would time pass faster on the moon? it is also a satellitte of the Earth. And how much faster would time pass on the moon?

 

A quick calculation (by no means certain) shows that a clock would run about 57 microseconds a day faster on the moon.

[noz92]

How did you calculate that?

[swansont]

The fractional frequency or time difference is (GM/r)/c² for the gravitational redshift. I caclulated a value for each, multiplied by 86400 and got (IIRC) several parts in 10¹⁰ for the earth and a couple in 10¹¹ for the moon - about 60 microsec/day for the earth and 3 for the moon. So, relative to deep space, clocks run slow by this amount. But relative to us, the moon runs faster.

 

I also calculated the kinetic term, which is (1/2) v²/c² but this term is much smaller - the moon isn't moving very fast.

 

feel free to check my math, though.

[The Nacho]

Wait...if time goes slower the more gravity you get...then, wouldn't the inside of black holes not be affected by time? (Which would mean that you can't go through a black hole to another universe) And, if you stopped time with gravity, the gravity would still be there, wouldn't it? I have one more question: If you stopped time with gravity, how would you start time back up again? How would you get rid of the gravity if you were stopped in time?