Hi There is a (possibly bogus) story from the early days of GPS:
The Cesium standards were specified with a tuning range of X. That all was fine on earth. The gotcha was that the frequency change in orbit was a significant percentage of X. Simply put, the guys who did the spec “didn’t believe” in relativity (or at least didn’t do the math). When this all came up a crash course in physics was arranged and the spec was changed. Bob > On May 20, 2016, at 1:00 PM, Tom Van Baak <[email protected]> wrote: > > Hi Peter, > > Good question. And, yes, it would work to use GPS. > > But we don't do it that way because it's a poor physics demonstration to use > a highly complex system that *already* takes relativity, propagation delay, > gravity and elevation into account (GPS) as a tool to then "detect" > relativistic effects in a portable cesium clock at high altitude. > > The clearest demonstration, one free from needing to know anything or > everything about GPS, one that avoids circular proof, is just to use two > identical synchronized portable clocks. So that's why and what we did. > > Alternatively, a really nice *thought* experiment is -- if your GPS receiver > firmware, and if the entire DoD infrastructure eliminated all notions of > relativity for one day. Everyone would then get a wonderful lesson on why > relativity is important in a satellite-based PNT system like GPS. Hint: it > would screw up 1PPS timing and UTC by tens of microseconds, but as far as I > can tell, it would distort positioning only by a small fraction of a meter. > > The nearest we have to this thought experiment was the pre-GPS experiment > done with NTS-2 in 1977. Read, or at least look at the plots at the end of: > http://leapsecond.com/history/Ashby-Relativity.htm > http://leapsecond.com/history/1978-PTTI-v9-NTS-2.pdf > > /tvb > > ----- Original Message ----- > From: "Peter Reilley" <[email protected]> > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Sent: Friday, May 20, 2016 8:24 AM > Subject: Re: [time-nuts] GENIUS by Stephen Hawking (PBS TV), with 5071A > cesium clocks > > >> I have a question. I, of small brain, am wondering: if the time >> difference between the >> top of the mountain and the bottom of the mountain is 20 nS over 24 >> hours could you >> repeat the same experiment using GPS? The time difference of 20 nS is >> measurable >> using GPS. >> >> The GPS clock must run faster on the mountain top than the GPS at the >> mountain >> base and yet the two remain synchronized to the satellite reference. >> Therefore >> the GPS 1 PPS signal (measurable to a few nS) must be wrong in in one of >> the local >> frame references. >> >> My brain hurts. >> >> Pete. >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
