"Norbert_Paul" <email@example.com> wrote in message news:firstname.lastname@example.org... > Tom Potter wrote: >> "Sam Wormley"<email@example.com> wrote in message >> news:ypKdnctDJ_vmQjDMnZ2dnUVZ_rmdnZ2d@giganews.com... >>> On 6/3/13 11:52 PM, Tom Potter wrote: >>>> Sammy, how do you think special relativity compares to Maxwell's >>>> Equations, Newton's Laws, Ohm's Law, Kirchoff's Laws... >>> >>> All working tools of physics, Potter. >> >> The issue is: >> >> "Why are so many impressionable people, >> so fixated on Relativity, >> >> considering that overall >> it wastes time, money and minds > Well, actually we are a clandestine sect where > c is our God and St. Albert is the prohet. > >> whereas many other tools of physics >> are more widely used and >> have a far more POSITIVE impact on society? > The golden rule directly follows from relativity: > What is good and what is bad depends on the observer. > Hence, play safe when doing questionalbe things. > You are not sure if you are the oberver at the bad > side. > >> Is it possible that the Mass Media >> has brainwashed impressionable people >> to believe that Relativity is a better "tool"? > No. It is not the media. We are clandestine as I > told you before. > >> Do you think that people >> should get a reasonable rate of return >> for the time, mind and money >> they expend acquiring information about a "tool". > The blessings of c are our return. > A:"mc^2 = En" > >> Considering that a pipe wrench is a more useful "tool" >> than Relativity, >> do you think that it would be a good idea for >> the Mass Media to hype pipe wrenches >> and for schools to have many classes >> and much discussion about pipe wrenches. > Yes, definitely! For forward for it! > > But I haven't heard of, say, GPS-positioning > being adjusted by pipe-wrences. Can you be more > percise on that? How is your navigation assistant > adusted by pipe wrences? Or don't you use any? > Is such object witche's brew to you? > Besides you can easily identify members of our > sect. Everyone of us adores his navigation > assistant on his altar in his car. > >> It is my perception that if someone needs a "tool" >> to do a job, they will find one or create one. > Curiosity and scientific interest is a tool, too. > It leads to other tools of yet unforseeable use. > You surely must know of Daniel C. Stillson. > >> For example, at this time >> "tools" are needed to acquire more energy >> and to use energy more efficiently. >> Do you think this "need" will >> result in new "tools" to do the job? > No. You already have a pipe wrench. > >> A mind is a terrible thing to waste. > Who do you mean?
Thanks to my pal "Norbert_Paul" for demonstrating how people have been conditioned by the Mass Media to believe that Relativity is/was essential to the design, operation and maintenance of the GPS System.
Here is how the GPS system actually works.
If my pal "Norbert_Paul" reads and understands this, he will understand that relativity is not needed to design, engineer and maintain the GPS System.
1. Light travels at a constant speed "c" of about 299 792.458 meters per second in the absence of matter, and in media with sparse matter, such as the Earth's atmosphere.
2. Time interval measurements of E-M waves in air, and space, are equivalent to distance measurements.
distance = time interval * c
3. Synchronized clocks can be used to quantize the distance between the points by measuring the time it takes light/radio waves to travel from one point to another.
Clock(A) sends a message that it is time(X). Clock(B) notes that it is time(X) + I1 on its' clock.
The distance between the clocks is I1 * C
In other words, systems of synchronized clocks can quantize the distances between the clocks, by transmitting the time at each clock's location.
Any clock can determine the distances between it and other clocks, by simply determining time(I) for all of the other clocks.
For example, if one measures a time delay of "I1" of a radio wave from New York, they must be somewhere on the surface of a sphere, with a distance radius of I1 * C, centered about New York
If they also measure a time delay of "I2" of a radio wave from San Francisco, they must be somewhere on the surface of a sphere, with a distance radius of I2 * C, centered about San Francisco.
If they measure both, they must be on a circle represented by the intersection of the two spheres.
As can be seen, the measurement of a third point, would be the intersection of the circle with another sphere, and would let tell the observer that they are on one of two points.
A fourth measurement would resolve the situation, and tell them at which of the two points they are located.
4. As the GPS satellites are moving, whereas New York and San Francisco are located at fixed points (With respect to Earth bound observers.), it is necessary that GPS receivers know where the satellites were when they transmitted the time.
This is handled, by having each satellite transmit its' position in space, along with the time data.
Each satellite not only transmits where it is ("ephemeris data"), it transmits its' orbital data ("almanac data"), along with its' time.
The "ephemeris data" serves the same purpose to the GPS receiver, as the Sun does is to a sailor with a sextant.
5. Ground stations continuously monitor the satellites' orbits and transmissions, and when changes exceed certain amounts, signals are sent to the offending satellites, updating their "almanac data", their "ephemeris data", their time settings, and drift in their clocks with respect to the master clock on Earth.
In other words, the ground station monitors the data transmitted by the satellites and when necessary sends them signals that tells them, that their clock is x nano-seconds fast, their orbit has changed to such and such (Perhaps because of dust drag, etc.), that their "ephemeris data" should be xxx, etc.
6. As portable GPS receivers do not have extremely stable oscillators, they must derive precision times from the satellites.
As the satellites are at an altitude of about 11,000 miles, (From the center of the Earth.) and radio waves travel 186,000 miles in one second, it takes about .006 seconds for the time, ephemeris, and almanac data to reach a sea level receiver.
This means that in a typical transmission, the GPS receiver must subtract about .006 seconds from its' clock, in order to set its' clock. GPS receivers receive and average the times from several satellites, and recursively home in on the master time, and make an adjustment for recursively computed position of the satellite.
In other words, at the reception of the first data, the GPS receiver knows the master time to about .006 seconds higher than the first time it receives, and as it picks up signals from other satellites, and recursively computes the distances to the satellites, and averages out multi-path signal variations, its' own clock homes in on the master clock time.
As the satellites take about 12 hours (43200 seconds) to orbit the Earth, and the ephemeris data takes about .006 seconds to reach the receiver, this means that the GPS receiver knows where the satellite is to an accuracy of about one part in 43000 / .006 = 71600000 parts, even without clock and ephemeris corrections.
Considering that the Earth is about 24,000 miles or 126,000,000 feet in circumference, this amounts to a sphere of uncertainty of about two feet.
7. The clocks used in the GPS system are extremely stable. They have a long term and short term stability of about 1 part in 10^14 over one day and even months.
As there are about 3 x 10^13 MICROseconds in a year, this means that the GPS clocks can maintain microsecond agreement for over a year, even if no corrections are made.
But of course, adjustments ARE made to the clocks on a regular basis by a ground clock, to which all of the GPS clocks are referenced to.
8. As the satellites have a life expectancy of about 10 years, their orbits are very stable. In other words, when ground stations get a fix on a satellite's orbit, we know pretty much where the satellite will be for a long time, and GPS receivers on the ground have an extremely dependable target to sight on
9. There is some variation in the time it takes the signal to reach the receiver due to multi paths taken by the radio wave to the GPS receiver, so GPS receivers are programmed to compute out the multi-path variations, and to compute the time, using the most reliable data it gets from several satellites.
10. The GPS satellites broadcast on two carrier frequencies: L1 at 1575.42 MHz and L2 at 1227.6 MHz. They transmit a "coarse acquisition code" at 1.0 bits per nanosecond and a "precision code" at a bit rate of 10.230 bits per nanosecond.
Frankly the usefullness of the "precision code" is vastly overrated as current commercial GPS receivers have the capacity to phase lock with the carrier frequency.
As light travels at about 300,000,000 meters per second, or 300 meters in one micro-second, a one nano second error would result in an error sphere of about .3 meters ( One foot), and a 10 nanosecond error would result in an error of about 3 meters or ten feet.
By averaging data from multiple satellites, a receiver can reduce the timing uncertainty due to multipaths, and can reduce the error sphere by only averaging where the error spheres of several satellites overlap.
The single largest contributor to time transfer uncertainty is path delay, the delay introduced as the signal travels from the satellite to the receiver.
Quasi-random numbers are used to identify each satellite, and can be used measure the time interval most accurately.
The GPS receiver performs auto-correlations on the signal to identify each satellite
and can be used minimize the jitter in the leading edge of the transmitted signal, caused by transmitter noise, receiver noise, environmental noise, multipath signal combining, jamming, etc.
In other words, a segment of the quasi-random signal is incrementally delayed, and multiplied by the signal stream.
<If two strings of random numbers are multiplied, a maximum occur when and if the strings match, otherwise the product tends toward zero.>
In summary, the largest contributor to time transfer uncertainty is caused by variations path delay, due to signals reflected off mountains, buildings, etc., and as noted, much of the path delay errors can be averaged out, because the satellites are moving, and signals are received from several satellites,
and as radio waves travel at different speeds in denser media, the use of two transmitted frequencies can be, and is, used to minimize atmospheric effects.
The best GPS receivers can, by using the methods addressed above, reduce the uncertainty in time to about one nanosecond, which amounts to a sphere of uncertainty of about one foot.
I trust that if my pal "Norbert_Paul" reads and understands this post he will realize that IF relativity is used in the design, engineering, and maintenance of a GPS System or device it wastes time money and minds.