SR/GR use absolute time to synchronize the GPS clocks with the ground clock.
in [Physics]
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From: kenseto on 24 Mar 2010 09:27 On Mar 23, 12:51 pm, moro...(a)world.std.spaamtrap.com (Michael Moroney) wrote: > kenseto <kens...(a)erinet.com> writes: > >Hey idiot time dilation got nothing to do with this discussion. > > Time dilation has *everything* to do with this discussion. Time dilation > would cause the GPS satellite to "transmit" at the wrong frequency (as > far as a terrestial receiver is concerned), so they adjusted the frequency > before launch so it would at the correct frequency on Earth. Sigh...the discussion was about whether observed doppler shift will effect the rate of a clock. The answer is no. The rate of a moving clock is 1/gamma at all time. Ken Seto
From: kenseto on 24 Mar 2010 09:37 On Mar 23, 12:57 pm, moro...(a)world.std.spaamtrap.com (Michael Moroney) wrote: > kenseto <kens...(a)erinet.com> writes: > >Let me expain to you once again: In SR the rate of a clock moving wrt > >you is 1/gamma at all time. The GPS clock sends sends a signal to the > >ground clock after the passage of N+4.15 periods of Cs 133 > >radiation....when the ground clock receives this signal it will know > >that the passage of N periods of Cs 133 radiation on its clock have > >taken place. > > Yes, just like the train horn. The approaching train has to sound at a > frequency lower than 440 Hz to be heard at the station as 440 Hz, while a > departing train has to sound at a higher frequency to be heard as 440 Hz. No it's not the same. The GPS sends a signal after N+4.15 perods of Cs 133 radiation elapsed....no matter if it is approaching the ground clock or receding away from the ground clock. The ground clock will know N periods of cs 133 radiation have elapsed on the ground clock. With your situation the audience at the platform will hear 440 Hz when the train is approaching but they will hear a different frequency when the train is receding away from the platform. Ken Seto > > Same effect, different causes.
From: Sam Wormley on 24 Mar 2010 11:14 On 3/24/10 8:27 AM, kenseto wrote: > Sigh...the discussion was about whether observed doppler shift will > effect the rate of a clock. The answer is no. The rate of a moving > clock is 1/gamma at all time. > > Ken Seto Let the clock be a distant pulsar with radial velocity v with respect to the observer. The relativistic formula for the Doppler shift in pulse arrival time due to an arbitrary velocity is given by t' = (1 + v/c) γ t where v represents the velocity along the line of sight between source and observer and t' and t represent the time between pulses at the observer and at the source, respectively.
From: Michael Moroney on 24 Mar 2010 11:32 kenseto <kenseto(a)erinet.com> writes: >On Mar 23, 12:51 pm, moro...(a)world.std.spaamtrap.com (Michael Moroney) >wrote: >> kenseto <kens...(a)erinet.com> writes: >> >Hey idiot time dilation got nothing to do with this discussion. >> >> Time dilation has *everything* to do with this discussion. Time dilation >> would cause the GPS satellite to "transmit" at the wrong frequency (as >> far as a terrestial receiver is concerned), so they adjusted the frequency >> before launch so it would at the correct frequency on Earth. >Sigh...the discussion was about whether observed doppler shift will >effect the rate of a clock. The answer is no. The discussion is about how different physical effects cause a frequency shift, and these frequency shifts can be calculated in advance and compensated for so that a relatively moving target receives a correct frequency. The passengers aboard the train will sense the "A" horn as mistuned. But those on the platform will hear the correct tune due to Doppler and some physics math. Someone riding aboard a GPS satellite will think the cesium clock is mis-set, with an incorrect divisor. A GPS receiver on the ground gets the correct frequency due to SR, GR and precalculated physics math that set the "wrong" divisor before launch. Same effect, different causes.
From: Michael Moroney on 24 Mar 2010 12:02
kenseto <kenseto(a)erinet.com> writes: >On Mar 23, 12:57 pm, moro...(a)world.std.spaamtrap.com (Michael Moroney) >wrote: >> >> Yes, just like the train horn. The approaching train has to sound at a >> frequency lower than 440 Hz to be heard at the station as 440 Hz, while a >> departing train has to sound at a higher frequency to be heard as 440 Hz. >No it's not the same. The GPS sends a signal after N+4.15 perods of Cs >133 radiation elapsed....no matter if it is approaching the ground >clock or receding away from the ground clock. There are additional Doppler effects on the GPS signal as the satellites approach or recede, but I'm not talking about that. Don't try to confuse matters by mixing the Doppler of the GPS signals and the Doppler train example. Consider the signal from a satellite as it passes directly overhead, so that it is neither approaching nor receding. Doppler effect is zero. However since the satellite is not as deep in the earth's gravity well, there are GR effects. In addition the satellite is moving at a decent clip so that there are SR (NOT Doppler!) effects. With the cesium clock "mis-set" so that the divisor is N+4.15 periods of Cs, the received signal on earth's surface is absolutely correct. (remember, no Doppler in this case). >With your situation the audience at the platform will hear 440 Hz when >the train is approaching but they will hear a different frequency when >the train is receding away from the platform. Remember, I changed the concert so that the train is receding for the entire performance, just for you. The Doppler effect on the performance is constant. You could also argue that the SR and GR effects on the satellites would change as the satellites speed up and slow down in their orbits, or move into higher and lower orbits. However, the satellites don't do that, so the SR/GR compensation factor is constant. Once again, same effect (frequency shift), different causes (SR/GR vs. Doppler) |