[McQueen]

Alan Calverd: I don't have a problem with the gravitational shift of GPS satellite clocks - it's a simple computation built into the firmware. Aiming a gun at  moving target is a bit of an art, but you can learn to synchronise the arrival of the shot with the predicted position of a bird. Though squirrels are more difficult because they run in random spurts.

This is how the GPS system works:

“Each GPS satellite continuously transmits a radio signal containing the current time and data about its position. Since the speed of radio waves is constant and independent of the satellite speed, the time delay between when the satellite transmits a signal and the receiver receives it is proportional to the distance from the satellite to the receiver. A GPS receiver monitors multiple satellites and solves equations to determine the precise position of the receiver and its deviation from true time. At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time).”

Nothing in that passage as far as I can see about special relativity. Gravity does play a part in speeding up clocks, therefore regardless of whether it is a digital clock or a mechanical one, if gravity pulls on the components with less force, the clocks will speed up. This is exactly what happens when clocks are placed in satellites many hundreds of kilometres above the earth’s surface where the force of gravity is weaker. The fact that clocks speed up does not mean that gravity effects time itself! Further common sense tells us that if General Relativity makes a difference then special relativity should also make a difference with 4 satellites up in space, surely each would be measuring time in a different way from the others, since each is viewing the others through its own frame of reference? How would the software adjust for that? As I said special relativity is untenable by any standard.

[McQueen]

 

Bored Chemist: Space isn't getting "chopped"; what would be in the gap between the two bits of separated space?

Why don't you tell me. You are the one supporting the twin paradox where the twins really do have different ages after one goes off into space travelling at some fraction of the speed of light while the other remains at home. You might as well ask, what happened to the years that the twin in space lost or the twin on the ground gained?  You are using a ridiculous etymology...

[Bored chemist]

Nothing in that passage as far as I can see about special relativity.

Then don't pretend it is relevant.

Find a better passage, like this one.
https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Special_and_general_relativity

. You might as well ask, what happened to the years that the twin in space lost or the twin on the ground gained?

Time passed at different rates for the two people. So what?
Why is that difficult?

How would the software adjust for that?

I don't know and I don't care.
But my GPS works, so I know that the software does the job.

Of course it helps that you are wrong about this.

if General Relativity makes a difference then special relativity should also make a difference with 4 satellites up in space, surely each would be measuring time in a different way from the others, since each is viewing the others through its own frame of reference?

They are all in free fall. So they all experience exactly the same gravitational effects/
So they all keep time WRT each other.
There's nothing for the software to correct on that score.

Gravity does play a part in speeding up clocks, therefore regardless of whether it is a digital clock or a mechanical one, if gravity pulls on the components with less force, the clocks will speed up.

Why?
And why is the extent of the change exactly that which is calculated by GR?

[Halc]

This is how the GPS system works:

“Each GPS satellite continuously transmits a radio signal containing the current time and data about its position. Since the speed of radio waves is constant and independent of the satellite speed, the time delay between when the satellite transmits a signal and the receiver receives it is proportional to the distance from the satellite to the receiver. A GPS receiver monitors multiple satellites and solves equations to determine the precise position of the receiver and its deviation from true time. At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time).”

Nothing in that passage as far as I can see about special relativity.

Nothing in that passage concerning gravity or other relativistic adjustments they decide to put into its design either. You've simply not chosen a passage that gets into those details since it is fairly irrelevant to how it works, but very relevant if you're actually engineering the system.

Gravity does play a part in speeding up clocks, therefore regardless of whether it is a digital clock or a mechanical one, if gravity pulls on the components with less force, the clocks will speed up.

It is not a function of gravitational force, but rather gravitational potential.  A clock at the center of Earth will be more dilated than one at the surface despite no gravitational force there.  The potential is lower there, and that's what counts.

The fact that clocks speed up does not mean that gravity effects time itself!

Technically, it is the geometry of spacetime (which is distorted by the presence of mass) that effects time itself.

Further common sense tells us that if General Relativity makes a difference then special relativity should also make a difference with 4 satellites up in space, surely each would be measuring time in a different way from the others, since each is viewing the others through its own frame of reference?

SR very much needs to be taken into consideration by said engineers, else the system will not work.  Yes, each satellite is moving relative to any of the others, so none of their clocks are in sync in any satellite's momentary inertial reference frame.  So what? They're not 'viewing' each other.  We on Earth listen to them all, and we must track how far out of sync they grow over time.

Look at the ISS clocks, which run slower, not faster, despite being in orbit just like the GPS satellites. SR explains it, despite your seeming denial of its effects.

How would the software adjust for that? As I said special relativity is untenable by any standard.

All these fancy posts about how it works, but always twisted, typical of a denier.  .

The GPS satellites move at a fairly constant speed relative to Earth, so the clocks are adjusted to compensate accordingly. The software only need deal with deviations from perfect orbits, and these deviations are significant, especially with the moon up there yanking everything this way and that.

[alancalverd]

As I said special relativity is untenable by any standard.

And yet I navigate hundreds of miles above the clouds and end up in the right place (within 5 degrees of the runway), at the correct height (within 50 ft) entirely due to everyone else's understanding of relativity.

How sad that my life depends on something you don't believe in. - it's like religion in reverse!

[Bored chemist]

Perhaps McQueen should enrol in a university physics classand pester then to do this
That way, he can see relativity in action with his own eyes.
https://arxiv.org/abs/1108.5977

It's probably just about in the realms of what an amateur could do as a DIY set up.
That way you don't need to worry about conspiracy from "Big Science"

[alancalverd]

Ah, progress! In my day we (or at least I) didn't have a magnetic spectrometer or even a reliable surface-barrier detector to hand. We measured kinetic energy with a calorimeter and wavelength with a sodium chloride crystal and dental x-ray film. But undergraduates were mostly stoned and ready to believe anything in the Sixties.

[McQueen]

The problem as I see it is that many of the contributors and ‘experts’ on this forum desperately believe in Newton’s notion of absolute time and space and at the same time swear blind that Einstein’s special relativity is what works.  Yet the two points of view are incompatible. In special relativity lengths do really  contract and time  really  does dilate. One cannot claim to believe in special relativity and still harbour the hope that everything will work out and that the distance from London to New York will remain the same, whether you travel by turbojet or by prop plane. It doesn’t.  For instance :

“Everything is relative; it depends on your frame of reference. Different observers see different things if they are in different reference frames (i.e., they are moving relative to each other).”

Would most of you be in agreement with this statement, that different observers, moving relative to each other at constant speeds see different things, because they are in different frames of reference?

Here is another statement which is a little more clear:

Different observers (i.e., observers moving relative to each other) measure different times, lengths, and masses. Only spacetime is observer independent.

What is the difference? The difference is that Newton believed in absolute space and time, whereas Einstein created the notion of spacetime, where time and space were no longer immutable but changed according to the frame of reference (i.e., if the objects were moving relative to each other)  Note that this need not include relativistic speeds. Einstein frequently used trains in his examples.

Before 1905, scientists considered space and time as completely independent objects. Time could not affect space and space could not affect time. After 1905, however, the Special Theory of Relativity destroyed this old, but intuitive, view. Specifically, Special Relativity showed us that space and time are not independent of one another but can be mixed into each other and therefore must be considered as the same object, which we shall denote as space-time. The consequences of space/time mixing are:
•   time dilation
•   and length contraction.

 From the above it is obvious that if there are 4 GPS satellites and one  ground station, they are all moving with respect to one another and would measure different times. To claim that they are all falling through space at the same speed is wrong. Each satellite is at a slightly different altitude and hence all have different speeds. Which means that  they are in different frames of reference with regard to each other and therefore measure different times. Wikipedia not withstanding.

[alancalverd]

They don't measure time. They transmit time signals. The GPS receiver does the measuring.

[McQueen]

They don't measure time. They transmit time signals. The GPS receiver does the measuring.

Congratulations like Alice in the Caucus race, we are back at the beginning and who knows that may very well be the best place to be. 

[Bored chemist]

They don't measure time. They transmit time signals. The GPS receiver does the measuring.

Congratulations like Alice in the Caucus race, we are back at the beginning and who knows that may very well be the best place to be. 

Are you aware that, before launch, the clocks on the GPS satellites were carefully set to run at the wrong rate?

[alancalverd]

And resynchronisation is (theoretically) easy because all the ground stations know where they are. Or at least they think they do. There's nothing quite as upsetting to GPS as a tectonic plate shift, though rebuilding a runway can add a last-minute frisson for the user. Like the man said, New York ain't always where it used to be.

[hamdani yusuf (OP)]

Time dilation from STR and GTR have opposing effects to orbiting satellites.
 
https://en.wikipedia.org/wiki/Time_dilation#Combined_effect_of_velocity_and_gravitational_time_dilation

[hamdani yusuf (OP)]

The graph shows gravity potential due to a solid sphere. It should somehow be related to blue curve in previous graph.