Time dilation and Gravitational time dilation

[chrisgray]

Does the combination of Time dilation and Gravitational time dilation create an combined effect or do they act separately?

[IM Egdall]

Does the combination of Time dilation and Gravitational time dilation create an combined effect or do they act separately?

 

They combine. For example, clocks on GPS satellites must be corrected for both effects:

 

Time dilation: Atomic clocks on board GPS satellites run slower than clocks on Earth by about 7 thousand nanoseconds per day -- due to their motion relative to the Earth.

 

Gravitational time dilation: The satellite clocks run faster than Earth surface clocks by about 45 thousand nanoseconds per day -- due to their higher altitude.

 

Taken together, there is a net gain of about 45 -7 or 38 thousand nanoseconds per day. Since GPS needs an accuracy of 20-30 nanoseconds to work, the combined effect must be taken into account.

 

See link: http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

 

<br clear="all"> http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

 

[timo]

What's the difference between "combine" and "act separately" in this context, anyways?

[chrisgray]

does the relative time of an object equal zero at the event horizon of a black hole because the event horizon is at 2GM/c^2 and gravitation time dilation is

[elfmotat]

does the relative time of an object equal zero at the event horizon of a black hole because the event horizon is at 2GM/c^2 and gravitation time dilation is

 

To an observer an infinite distance away from the BH, yes.

[IM Egdall]

What's the difference between "combine" and "act separately" in this context, anyways?

 

The satellite clocks show a net (or combined) effect of both time dilation and gravitational time dilation.

[timo]

So what do you think satellite clocks would show if the two effects "acted separately"? Two times?

[juanrga]

Does the combination of Time dilation and Gravitational time dilation create an combined effect or do they act separately?

 

Gravitational time dilation is a subset of the general concept of time dilation

[swansont]

Gravitational time dilation is a subset of the general concept of time dilation

 

Since most people come at this from the perspective of learning special relativity first, it's not typically apparent. Even though general relativity is the general case, it doesn't really look that way when learning about time dilation. You see a kinematic effect, and a gravitational effect.