A question for you rocket scientists

[angela146]

How do the GPS satelites deal with the effect of gravity on time?

Here's the thing: time moves faster for objects that are closer to the earth (like you and me for example) whereas time moves slower for objects that are farther from the earth (gps satelites are about 18,000 miles up).

Yes, it's a small difference but the timing of these things has to be accurate to a couple of billionths of a second.

Wouldn't the clocks run slower in the satelites and thus throw off the calculations?

 

[Guest]

How do the GPS satelites deal with the effect of gravity on time?

Here's the thing: time moves faster for objects that are closer to the earth (like you and me for example) whereas time moves slower for objects that are farther from the earth (gps satelites are about 18,000 miles up).

Yes, it's a small difference but the timing of these things has to be accurate to a couple of billionths of a second.

Wouldn't the clocks run slower in the satelites and thus throw off the calculations?

gravity...its all relative.

 

[Weird Harold]

Yes, it's a small difference but the timing of these things has to be accurate to a couple of billionths of a second.

Wouldn't the clocks run slower in the satelites and thus throw off the calculations?

Yes, the clock would run slower, but it's not the time of day that has to be measured in picoseconds, but the time difference between three or more satelites. Since all of the satelites are affected the same by relativistic time dilation the time difference in when the signals arrives at a GPS receiver is unaffected by time dilation.

PS: it's not gravity but relative velocity that causes time dilation.

 

[Guest]

Yes, the clock would run slower, but it's not the time of day that has to be measured in picoseconds, but the time difference between three or more satelites. Since all of the satelites are affected the same by relativistic time dilation the time difference in when the signals arrives at a GPS receiver is unaffected by time dilation.

you're such a wonderful brainiac.

 

[S-Des]

Yes, the clock would run slower, but it's not the time of day that has to be measured in picoseconds, but the time difference between three or more satelites. Since all of the satelites are affected the same by relativistic time dilation the time difference in when the signals arrives at a GPS receiver is unaffected by time dilation.

PS: it's not gravity but relative velocity that causes time dilation.

Good lord...is there anything you don't know about?

 

[sickpuppy123]

Yes, the clock would run slower, but it's not the time of day that has to be measured in picoseconds, but the time difference between three or more satelites. Since all of the satelites are affected the same by relativistic time dilation the time difference in when the signals arrives at a GPS receiver is unaffected by time dilation.

PS: it's not gravity but relative velocity that causes time dilation.

Add one more factor. I don't know the satelites speed but it has to be less than 18,000 MPH since this speed causes all satelites to escape earth orbit. The speed of light is 186,000 MILES PER SECOND....or 669,600,000 MPH. Any time compression is insignificant for the purpose of measuring distances on the face of the earth. In addition to which GPS works on the difference from at least 3 satelites which ALL are subject to the same time shift and can therefore be calculated out of the equasion.

 

[angela146]

gravity...its all relative.

Yes, my relatives can be really slow

 

[angela146]

Yes, the clock would run slower, but it's not the time of day that has to be measured in picoseconds, but the time difference between three or more satelites. Since all of the satelites are affected the same by relativistic time dilation the time difference in when the signals arrives at a GPS receiver is unaffected by time dilation.

Thank you. Now it makes sense.

 

[angela146]

Add one more factor. I don't know the satelites speed but it has to be less than 18,000 MPH since this speed causes all satelites to escape earth orbit. The speed of light is 186,000 MILES PER SECOND....or 669,600,000 MPH. Any time compression is insignificant for the purpose of measuring distances on the face of the earth. In addition to which GPS works on the difference from at least 3 satelites which ALL are subject to the same time shift and can therefore be calculated out of the equasion.

Welcome to the AH!

 

[NoJo]

Angela, good question. After plugging in the speeds into the simple realtivity formula for time dilation 1 - (v squared / c squared), I found that as you suspected, the difference was signifant.

This link provides the answer to your question:

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

 

[rgraham666]

Cool link, Joe! Thanks.

 

[Oblimo]

You can measure time-dilation from the bottom of a skyscraper to the top if you have enough bored physicists and atomic clocks.

 

[TxRad]

You can measure time-dilation from the bottom of a skyscraper to the top if you have enough bored physicists and atomic clocks.

I bored a physicist one time and you wouldn't believe what I found inside......

I'm just glad she wasn't a relative at the time.....