<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Rudolf</i>
<br />Could he have gotten the same wrong results at different locations (heights, day, time)?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">I have my own ideas what went wrong. But does it matter? The GPS result leaves no room for options here.
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">How does the GPS system 'show' the speed of light<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The atomic clock on each satellite sends a signal toward Earth every 1.5 seconds. The message with the signal includes the satellite's orbit and location at the time of transmission. (This is checked with traditional optical photographs, and with laser ranging from other ground stations, and with dynamical constraints imposed by the time it takes the satellite to complete one period and return to the same spot.) A ground receiver picks up these signals from as many satellites as it can and figures out the exact distances to each satellite. It then triangulates its own position. With high-precision GPS, this triangulation is successful to within 1 meter. That could not happen consistently unless the legs of the triangles (the distances to the satellites) were of comparable accuracy.
For your purposes, the crucial point is how the ground receiver measures the distances. To simply many unneeded matters, let's assume the receiver is at a Monitor Station which has its own atomic clock and an already known location. (Then we already know the distances; but we can still compare to the GPS measures of distance.) Then the GPS measure of distance from Monitor Station to satellite is simply c(t2-t1), where c is the speed of light in the ECI frame, t1 is the transmission time, and t2 is the reception time. These must be measured to a nanosecond or so, during which time light moves about one foot or so.
See a diagram and formulas at
metaresearch.org/solar%20system/gps/absolute-gps-1meter-2.asp
.
It should then be obvious that, if c is at all variable, this method of getting distances will fail badly, and the system cannot work. But it works very well indeed. The largest possible error in c, under the most pessimistic set of assumptions about systematic errors, is +/- 12 m/s. -|Tom|-
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