Many here have argued that GPS supports or proves Relativity. I thought perhaps you might like the opportunity to explain why a surface clock and an orbital clock do not produce the correct relative velocity time dilation affect and they shift the correction to earth's central inertial frame - The pole. It seems GPS actually favors Lorentz over Einstein. Oh. GR fairs better but not perfect either. ******************************************************* http://egtphysics.net/GPS/RelGPS.htm RELATIVITY AND GPS (Section I: Special Relativity) Ronald R. Hatch The satellites of the global positioning system (GPS) travel around the earth in 12-hour periods in near-circular orbits. All of the satellites contain extremely precise atomic clocks whose rates depend both upon satellite velocity and altitude. An observer bound to the earth, in an airplane or in a satellite may determine his precise location by obtaining signals from several satellites simultaneously. This paper discusses the implications of GPS on Einstein's special theory of relativity. A subsequent paper will discuss the general theory. Introduction "Relativistic" effects within the Global Positioning System (GPS) are addressed. Hayden  has already provided an introduction to GPS, so the characteristics of the system are not reviewed. There are three fundamental effects, generally described as relativistic phenomena, which affect GPS. These are: (1) the effect of source velocity (GPS satellite) and receiver velocity upon the satellite and receiver clocks; (2) the effect of the gravitational potential upon satellite and receiver clocks; and (3) the effect of receiver motion upon the signal reception time (Sagnac effect) . There are a number of papers which have been written to explain these valid effects in the context of Einstein's relativity theories. However, quite often the explanations of these effects are patently incorrect. As an example of incorrect explanation, Ashby  in a GPS World article, "Relativity and GPS," gives an improper explanation for each of the three phenomena listed above. The three effects are discussed separately and contrasted with Ashby's explanations. But the Sagnac effect is shown to be in conflict with the special theory. A proposed resolution of the conflict is offered. The Sagnac effect is also in conflict with the general theory, if the common interpretation of the general theory is accepted. The launch of GPS Block II satellites capable of intersatellite communication and tracking will provide a new means for a giant Sagnac test of this general theory interpretation. Other general theory problems are reviewed and a proposed alternative to the general theory is also offered. Velocity Effects upon the Clock Rates. The fundamental question of velocity is always: "Velocity with respect to what?" Ashby, in the opening paragraph of his abstract, states: Important relativistic effects arise from relative motions of GPS satellites and users, ... And Ashby also states, at the start of a section on time dilation: First, clocks in relative motion suffer (relativistic) time dilation,... But these statements are patently untrue of GPS. It may appear to be a subtle difference, but it is very important to note that the GPS satellites' clock rate and the receiver's clock rate are not adjusted as a function of their velocity relative to one another. Instead, they are adjusted as a function of their velocity with respect to the chosen frame of reference—in this case the earth-centered, non- rotating, (quasi) inertial frame. The difference is easy to illustrate. GPS receivers are now routinely placed on missiles and other spacecraft. Spacecraft receivers can be used to illustrate Ashby's error. For illustrative simplicity, let us assume two "Star Wars" spacecraft are equipped with GPS receivers. Let one of the spacecraft move in an orbit such that the spacecraft follows a GPS satellite at a close and constant separation distance. Let the second "Star Wars" spacecraft move in the same orbit but in the opposite direction. The nominal velocity of a GPS satellite with respect to an earth-centered non-rotating frame is about 3.87 kilometers per second. Using this frame, the computed clock rates should slow by: (1) For low velocity compared to the speed of light, the change in frequency is approximated by 1/2 (v/c)2. Using this expression, one obtains a frequency decrease of 8.32 parts in 1011 for GPS satellites. Now, consider the first "Star Wars" receiver, which is following the GPS satellite. Since it has the same velocity relative to the earth-centered non-rotating frame, its frequency will be reduced by the same amount as the frequency of the GPS satellite; and there will, therefore, be no apparent relativistic shift in frequency of the received signal. This is, of course, also what one would get using the special theory of relativity, since there is no relative velocity between the first "Star Wars" spacecraft and the GPS satellite. However, for the second "Star Wars" spacecraft moving in the opposite direction in the orbit, the results are dramatically different. Relative to the earth-centered non-rotating frame, this second spacecraft's speed is no different than the speed of the first spacecraft or the speed of the GPS satellite. Thus, the expected frequency shift is the same 8.32 parts in 1011. This means that, in the earth-centered non-rotating frame, there is no apparent relativistic shift in frequency between the second "Star Wars" spacecraft and the GPS satellite, even when the relative velocity between the spacecraft receiver and the GPS satellite is 7.74 kilometers per second (approaching each other at twice the orbital speed). But, if Ashby were right, the relativistic induced difference in frequency between this second "Star Wars" spacecraft and the GPS satellite would be 33.28 parts in 1011. (Four times the amount a receiver stationary in the earth-centered non-rotating frame would see.) Is this large discrepancy in expected frequency difference detectable? Not really. The special theory, in addition to claiming the frequency received is a function of the relative velocity, also claims that the speed of light is isotropic relative to the (observer) receiver; and the GPS system uses the earth-centered non-rotating frame and also assumes the speed of light is isotropic in that frame. Jorgenson , ironically calling upon work by Ashby, shows that, if one chooses a frame based upon the instantaneous velocity of the second "Star-Wars" satellite receiver, one gets exactly the same received-frequency difference when one combines the relativistic clock shift with the Doppler and aberration effects. Jorgenson makes the following statement: In considering alternative coordinate frames, the differences in special relativity exactly counterbalance those in classical Doppler. Einstein's special relativity is the great equalizer of coordinate systems. We are given the option of choosing the one most convenient to our needs, and in the case of GPS, this is an earth-centered inertial frame. But Jorgensen confuses the special theory claims with the claims of the Lorentz ether theory. Indeed, many people claim that they are equivalent. However, as we shall see later, there is direct experimental evidence which supports the Lorentz ether theory over the special theory. Whenever a frame is chosen which does not coincide with the receiver or observer, experiment demands that the speed of light be treated as non-isotropic as far as the receiver or observer is concerned. But this is anathema to the special theory, since it is a direct contradiction of the special-theory teaching that the speed of light is always isotropic relative to the observer (Einstein's "convention" that the round-trip time of a light pulse is composed of two equal time intervals for the outgoing and incoming pulse). And it is this aversion to non-isotropic light speed, as we will see later, which is responsible for the myriad attempts to explain the Sagnac effect without admitting that it simply arises from the choice of an isotropic frame in which the receiver is moving. Ashby is guilty of claiming that clocks run at a rate determined by their relative velocity. In fact, the rate at which clocks run must be computed using the clock velocity with respect to the chosen isotropic light-speed frame. This is consistent with the Lorentz ether theory but not with the special theory. *************************************************** Are not Relativists guilty of distorting facts (lying) to claim more support for their theory when we should now move back to Lorentz?