Is GPS consistent with relativity? (Split from is Relativity 100% proven)

[Le Repteux]

You are right, the clocks would not be sync this way, but it is the same for GPS clocks, except that it is the inverse process: we "un" sync them before launch, and they appear sync when in orbit. The idea is to better understand the sync process by inversing the tasks in a particular mind experience, that's all. If we really had to use relativity formulas to build the clocks, it would be another story, but I don't see where they could be useful. Do you?

[xyzt]

You are right, the clocks would not be sync this way, but it is the same for GPS clocks, except that it is the inverse process: we "un" sync them before launch, and they appear sync when in orbit.

No, it is not, you understood absolutely nothing, the clock on the ground and the clock in the satellite end up ticking at the same exact frequency. They also show the same exact elapsed time due to having the same exact offset from zero. You are not here to learn as you profess, you are here to push some fringe ideas.

 

 

 

If we really had to use relativity formulas to build the clocks, it would be another story, but I don't see where they could be useful. Do you?

 

Not how to build them but how they function.

Edited September 6, 2014 by xyzt

[swansont]

 

This is a better argument. Since it is local time that we want them to keep with precision, what would be the use to know about relativity to build atomic clocks? We do not use the formulas to build the clocks, do we?

 

Relativity is part of atomic physics, so not knowing relativity would limit the theory, and there are relativistic concerns in building improved atomic clocks. One motivation in building cold-atom clocks is reduction of the relativistic effects of the atomic motion. You wouldn't think to do that if you didn't know relativity. You would be confused why your beam clocks were giving different answers for different beam velocities or velocity spreads.

[Le Repteux]

You are right Swansont, if my mind experience would concern different clocks, it could not work, but if the clocks would be the same, if both would be cesium clocks for instance, should it work?

No, it is not, you understood absolutely nothing, the clock on the ground and the clock in the satellite end up ticking at the same exact frequency. They also show the same exact elapsed time due to having the same exact offset from zero.

Are you talking about the GPS clocks? Because I always thought that they had to be put out of sync so as to appear sync with the ground reference clocks once in orbit.

You are not here to learn as you profess, you are here to push some fringe ideas.

I do push some fringe ideas here, but I am now participating to a scientific subject where I know that I can't.

Not how to build them but how they function.

Swansont was talking about their internal mechanism, saying that my mind experience was hypothetically feasible.

Edited September 6, 2014 by Le Repteux

[swansont]

You are right Swansont, if my mind experience would concern different clocks, it could not work, but if the clocks would be the same, if both would be cesium clocks for instance, should it work?

 

Not if they were run under different conditions where the relativistic effects came into play.

[John Cuthber]

Is four pages a record for a discussion where it is clear from the outset that the answer is just "yes"?

 

EDIT to add

I note with ironic amusement that my post made this a 5 page pointless debate.

Edited September 7, 2014 by John Cuthber

[StringJunky]

John Cuthber, on 07 Sept 2014 - 12:06 PM, said:

Is four pages a record for a discussion where it is clear from the outset that the answer is just "yes"?

Just thinking along those lines myself.

[Le Repteux]

Swansont,

 

In my example with non relativistic doppler effect, we can easily sync the other ship's clock with ours because it is only a mechanical adjustment, because doppler effect is only a matter of frequency shift when it is not relativistic. But the GPS clocks are also adjusted mechanically, their frequency is slowed to account for gravity effects, so that they seem to be sync with our clocks when in orbit. If we can adjust the frequency of the ship's clock with ours without knowing why it is out of sync, why could not we do the same for a satellite clock? After all, if the orbit is circular and if we eliminate variables like doppler effect, it is only a matter of changing progressively the frequency of the orbiting clock until we can observe that it is sync with ours, no?

Edited September 7, 2014 by Le Repteux

[xyzt]

Swansont,

 

In my example with non relativistic doppler effect, we can easily sync the other ship's clock with ours because it is only a mechanical adjustment, because doppler effect is only a matter of frequency shift when it is not relativistic. But the GPS clocks are also adjusted mechanically, their frequency is slowed to account for gravity effects, so that they seem to be sync with our clocks when in orbit. If we can adjust the frequency of the ship's clock with ours without knowing why it is out of sync, why could not we do the same for a satellite clock? After all, if the orbit is circular and if we eliminate variables like doppler effect, it is only a matter of changing progressively the frequency of the orbiting clock until we can observe that it is sync with ours, no?

1. The orbit is not circlar

2. You cannot "eliminate" the Doppler effect since there is relative motion between the transmitter and receiver

3. As explained earlier, what you observe is not the frequency of the clock on the satellite but the value SHIFTED by the difference in speed and in gravitational potential. So, if you insist on trying to adjust the frequency WITHOUT the help of GR, as you have been trying throughout this thread, you CAN'T.

Edited September 7, 2014 by xyzt

[swansont]

. So, if you insist on trying to adjust the frequency WITHOUT the help of GR, as you have been trying throughout this thread, you CAN'T.

I'm at a loss to understand the perceived difficulty of measuring a frequency difference and driving it to zero.

[xyzt]

I'm at a loss to understand the perceived difficulty of measuring a frequency difference and driving it to zero.

You are "driving to zero" [math]f_{receiver}-f_{observed}[/math]. What you want is to drive to zero [math]f_{receiver}-f_{transmitter}[/math]. But you do not know [math]f_{transmitter}[/math]. You can only infer it, with the help of GR.

Edited September 7, 2014 by xyzt

[Le Repteux]

1. The orbit is not circular

If it was not, then it could be taken as a periodic effect an be accounted for as it is actually.

 

2. You cannot "eliminate" the Doppler effect since there is relative motion between the transmitter and receiver

By eliminating the doppler effect, I meant that we could realize it is due to direct motion and retrieve it from the adjustment of the clock's frequency.

 

3. As explained earlier, what you observe is not the frequency of the clock on the satellite but the value SHIFTED by the difference in speed and in gravitational potential. So, if you insist on trying to adjust the frequency WITHOUT the help of GR, as you have been trying throughout this thread, you CAN'T.

As far as the gravitation frequency shift is concerned, all we have to know for the GPS to work properly is that the observed frequency must be the same as our own clock's frequency, and all we have to do to obtain that is change the orbiting clocks' frequency step by step until it hits the right frequency. If we could not adjust the orbiting clocks from the ground, the question would be irrelevant, but we can, and we need to also because the clocks' rates are not exactly the same and they need to stay the same.

[swansont]

You are "driving to zero" [math]f_{receiver}-f_{observed}[/math].

Yes, that is precisely the situation that was proposed.

[Le Repteux]

You are "driving to zero" [math]f_{receiver}-f_{observed}[/math]. What you want is to drive to zero [math]f_{receiver}-f_{transmitter}[/math]. But you do not know [math]f_{transmitter}[/math]. You can only infer it, with the help of GR.

We can adjust the transmitter's frequency from the ground, and we can do it step by step until it is the same as our own clocks' frequency, in scientific research, it is called the heuristic method, and it is often used.

[swansont]

We can adjust the transmitter's frequency from the ground, and we can do it step by step until it is the same as our own clocks' frequency, in scientific research, it is called the heuristic method, and it is often used.

 

The point xyzt has been making is that the ground/space clock frequencies will not be the same (which is why they can't be synchronized). You have to differentiate between the clock frequency and the signal frequency that we measure in our frame, because they aren't the same. You have been sloppy in making this distinction.

[Le Repteux]

I always assumed that the clocks in orbit would not stay sync with the clocks on the ground if not adjusted to what you call their signal frequency, so I think that I made the distinction correctly between the clock frequency and the signal frequency. Does it matter that much if the relativity formulas were not absolutely necessary to the GPS? It would not change the fact that the clocks are drifting and that the drift is due to the limited speed of light, would it?

[xyzt]

Yes, that is precisely the situation that was proposed.

But what is needed is driving to zero [math]f_{receiver}-f_{transmitter}[/math]. You need to make the proper frequencies the same in order to have proper time pass at the same rate in both transmitter and receiver. The reason for that is that both devices integrate the proper time [math]\tau[/math] in order to get their respective coordinate times [math]t[/math]. (see the Ashby monograph). GPS works off coordinate time [math]t[/math] and coordinate time is obtained via : [math]t=\int{\sqrt{1-(v/c)^2}d\tau}[/math].

Edited September 8, 2014 by xyzt

[swansont]

I always assumed that the clocks in orbit would not stay sync with the clocks on the ground if not adjusted to what you call their signal frequency, so I think that I made the distinction correctly between the clock frequency and the signal frequency. Does it matter that much if the relativity formulas were not absolutely necessary to the GPS? It would not change the fact that the clocks are drifting and that the drift is due to the limited speed of light, would it?

 

That's just it: synchronization of the clocks implies the clocks have the same frequency and phase. So (as xyzt has said repeatedly) you can't synchronize the clocks. Synchronization is the wrong terminology to use.

 

Drift is another term that has a specific meaning: it's a noise process in a clock (others include flicker and random walk), and has nothing to do with relativity.

[Le Repteux]

That's just it: synchronization of the clocks implies the clocks have the same frequency and phase. So (as xyzt has said repeatedly) you can't synchronize the clocks. Synchronization is the wrong terminology to use.

I see what you mean, and I think that you saw what I meant too, but that xyzt did not, so I repeat more clearly: I was always talking of synchronizing the ground clock's frequency with the orbiting signal frequency while changing that signal frequency progressively from earth so that the observed signal frequency that we receive on earth equals the frequency of our reference clocks on earth.

 

Drift is another term that has a specific meaning: it's a noise process in a clock (others include flicker and random walk), and has nothing to do with relativity.

I did not know about these specific noises, thanks for the information. I used the term drift because I read it right here in the beginning, and I thought that its meaning fitted the relativity frequency shift quite closely. Since frequency shift fits both doppler effect and relativity effect at the reception of the signal, what specific terms could we use to differentiate them: would "doppler shift" and "reception shift" be OK? And what specific term could we use to talk about the relativity effect at the emission of the signal: would "emission shift" be OK?

Edited September 8, 2014 by Le Repteux

[xyzt]

I see what you mean, and I think that you saw what I meant too, but that xyzt did not, so I repeat more clearly: I was always talking of synchronizing the ground clock's frequency with the orbiting signal frequency while changing that signal frequency progressively from earth so that the observed signal frequency that we receive on earth equals the frequency of our reference clocks on earth.

I saw it very precisely. This is what allowed me to point out the repeated error in your reasoning: you are not synchronizing the satellite clock with the Earth-bound clock.

[Le Repteux]

No, but as I tried to make clear, I was synchronizing the frequency of the signal from the orbiting clock, which is not its original actual frequency but which we can adjust from the ground, with the actual frequency of the Earth-bound clock.

Edited September 8, 2014 by Le Repteux

[xyzt]

No, but as I tried to make clear, I was synchronizing the frequency of the signal from the orbiting clock, which is not its original actual frequency but which we can adjust from the ground, with the actual frequency of the Earth-bound clock.

This doesn't do you or anybody else any good, as explained. The fact that IN REAL LIFE, the GPS receiver "down here" and the GPS transmitter "up there" end up ticking at the same frequency (courtesy of GR) should have given you the clue, long ago.

Edited September 8, 2014 by xyzt

[Le Repteux]

Yes, they end up ticking at the same frequency, but if we let them run for a long while without adjusting them, they will get out of sync just as if we had never adjusted them before launch, what would not prevent us from adjusting them again to the right frequency since we can adjust them from the ground. To me, the fact that we could do that means that we could have adjusted them progressively once in orbit instead of adjusting them in one shot prior to launch.

Edited September 8, 2014 by Le Repteux

[xyzt]

Yes, they end up ticking at the same frequency, but if we let them run for a long while without adjusting them, they will get out of sync just as if we had never adjusted them before launch, what would not prevent us from adjusting them again to the right frequency since we can adjust them from the ground. To me, the fact that we could do that means that we could have adjusted them progressively once in orbit instead of adjusting them in one shot prior to launch.

It really doesn't matter what it "means to you". It matters what it means to mainstream scientists in charge of building and maintaining GPS. The adjustments are to counter the effects of temperature, altitude variation, clock drift, etc., i.e. the small DEVIATIONS from the prescribed frequency. The corrections, contrary to your insistence, cannot and will not replace the process of SETTING the frequency at launch. Because, without knowing GR , you do NOT know what value to set the frequency.

Edited September 8, 2014 by xyzt

[Le Repteux]

Since you say that you are synchronized with the main stream scientists, I accept to stop arguing, but make sure you stay adjusted with them!