Thread: TFF Shuttle View Single Post
October 14 2012, 06:15 AM   #28
Crazy Eddie

Re: TFF Shuttle

 B.J. wrote: ^ Uh, you know that the only reason your GPS works the way it does is because we've had to compensate for the relativistic effects of the satellites' motion, right?
Wrong. Turns out the clocks on GPS satellites are periodically re-synchronized with the ground clocks anyway (every thirty days, I'm told). Even if they weren't, the actual delay due to relativistic time dilation is about 200 picoseconds; this is an order of magnitude less than the inherent delay from electrical propagation in the receiver's actual antenna, which ISN'T accounted for, and cannot be.

Others already beat me to it, but like a lot of things related to relativity, there's a lot more myth than fact floating around.

The Librarian wrote:
FKnight wrote:
 B.J. wrote: ^ Uh, you know that the only reason your GPS works the way it does is because we've had to compensate for the relativistic effects of the satellites' motion, right? As for all that other nonsense, I don't even know where to start....
That gets stated a lot by pro-relativists, but it's not actually true. Determining your location via GPS is based on the differences between the time signals of various satellites and not in any way based on the difference between a satellite time signal and the device's Earth surface local time, as is commonly incorrectly believed. http://www.physicsmyths.org.uk/gps.htm

GPS computes time differences between satellites all moving at the same speed relative to each other. GPS doesn't care what time it is where you're standing relative to the satellites. Relativity is irrelevant to GPS.
No, you still have to compensate for relativistic differences between the satellites and the receivers
You don't actually "have" to, since the only applicable affect is due to gravity and the velocity of the satellites is irrelevant. The resulting error would still be a handful of centimeters even if it wasn't compensated for (which is still considerably higher than it would be if you account for special relativity).

Mind you, I'm not saying the GPS system doesn't contain an algorithm to account for relativistic time dilation. I'm saying that if they do, they hardly DEPEND on it, and would in fact be just as accurate without it. Like the Twin Paradox, it's just another piece of relativity mythology that nobody ever bothers to examine closely.
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Last edited by Crazy Eddie; October 14 2012 at 07:00 AM.