Global Positioning System (GPS) and Relativity - a rebuttal

Discussion in 'Physics & Math' started by James R, Jun 13, 2005.

  1. James R Just this guy, you know? Staff Member

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    I quote here from an article by John Baez, titled "Some Scientifically Inaccurate Claims regarding Cosmology and Relativity", which can be found here:

    http://math.ucr.edu/home/baez/RelWWW/wrong.html#gps

    The entire page is well worth a read, but in this post I will concentrate on Baez's description of the Global Positioning System (GPS).

    MacM, a well known crank on sciforums, has filled numerous threads with the claim that the GPS system does not use Einstein's relativity, and that in fact using relativity would mean that the GPS system wouldn't work. This is utterly wrong, since the system was designed and tested using that very theory.

    It appears MacM has borrowed most of his views from Tom Van Flandern, who Baez refers to in his article.

    Anyway, I now summarize Baez's explanation of how GPS relies on relativity, by extracting some relevant statements. Again, I urge you to read the entire article, if you're interested. The following is by Baez:

    --------

    In a paper remarkable chiefly for the extraordinary number of obvious errors it contained (see above), Tom Van Flandern, ("The speed of gravity-- what the experiments say" Phys.Lett.A 250 (1998) 1-11, also available here), stated:

    the Global Positioning System (GPS) showed the remarkable fact that all atomic clocks on board orbiting satellites moving at high speeds in different directions could be simultaneously and continuously synchronized with each other and with all ground clocks. No "relativity of simultaneity" corrections, as required by SR, were needed. This too seemed initially to falsify SR. But on further inspection, continually changing synchronization corrections for each clock exist such that the predictions of SR are fulfilled for any local co-moving frame. To avoid the embarrassment of that complexity, GPS analysis is now done exclusively in the Earth-centered inertial frame (the local gravity field). And the pre-launch adjustment of clock rates to compensate for relativistic effects then hides the fact that all orbiting satellite clocks would be seen to tick slower than ground clocks if not rate-compensated for their orbital motion, and that no reciprocity would exist when satellites view ground clocks.​

    At first glance, Van Flandern here appears to be claiming that the fact that the GPS continues to operate with great accuracy has in fact disproven the predictions of str concerning moving clocks (Van Flandern doesn't mention the gtr effects, but they are also significant). On careful reading, in this paper he actually appears to be saying in effect that anything that can be explained using str can be explained just as well using the Lorentz ether theory (let), a theory which he has never specified but which is usually taken to be mathematically equivalent to str, but with a different interpretation of Lorentz transformations, one which most physicists since Lorentz's day have found implausible.

    ...

    Before we can understand why, contrary to Van Flandern's assertions, relativity theory is actually working just fine in the GPS, we need to understand the basic principles behind its design and daily operation, so I'll begin by explaining (in an oversimplified way) how the GPS works, what the most important non-relativistic sources errors are, and how they are overcome. Once this is out of the way, I'll discuss the relativistic sources of error, and how they are overcome.

    ...

    A good way to start thinking about the general principle behind GPS is as follows. Suppose you know your precise range r1 to an object S1 with precisely known position x1 (a point in E^3, ordinary Euclidean space). Then you know you are located somewhere on a sphere of radius r1 and center x1. Next, suppose you also know your precise range r2 to a second object S2, with precisely known position x2. Then you know you are located somewhere on the circle which is the intersection of the first sphere with the sphere of radius r2 and center x2. Now suppose you also know your precise range r3 to a third object S3, with precisely known position x3. If you know all three things at the same time, then you know you are located on one of the two points in which three circles intersect! This process is called trilateration by geographers.

    The basic idea behind GPS is to adapt this idea by providing users with a "constellation" of satellites as "orbiting landmarks", which always know their precise position with respect to the Earth's surface, as well as the precise UTC at their location, and which continually transmit this dual information at regular intervals. The current (Block 2) GPS constellation consists of (at least) 24 Earth orbiting satellites, called SV's, in circular orbits about 11,000 nm (20,200 km) above the Earth's surface (that is, 26,750 km above the center of the Earth), traveling at 4 km/sec, giving an orbital period of precisely twelve sidereal hours; that is, the satellites rotate once every twelve hours with respect to the fixed stars, not with respect to the Earth, which is of course itself rotating underneath the satellites. (The actual number of satellites in orbit varies from time to time because new ones are launched, with a Delta 2 rocket, as old ones begin to wear out. The design life of each satellite is 7.5 years.)

    This means that each satellite comes over the same location along the same track over a fixed location on the surface of the Earth every 24 hours, or rather, four minutes earlier each day; the four minute discrepancy is due to the Earth's advance in its own orbit around the Sun. Incidentally, a common question is: why are the satellites not in geostationary orbits, like many communication satellites? The answer is that geostationary orbits are only possible over the equator, and as we've seen, trilateration won't work unless you can measure your distance to satellites in more than one plane. Since the designers of GPS were also looking ahead to future space-based applications, e.g. actively steering spacecraft in perfect formation (despite buffeting from the solar wind) by keeping their position using GPS, arranging the satellites so that their orbital period is precisely 12 sidereal hours turns out to be the simplest choice.

    Each satellite is visible above the horizon of a stationary user for about five hours. The satellites each orbit in one of six equally spaced planes (sixty degrees apart), each inclined at about 55 degrees to the equatorial plane of the Earth, and with (at least) four SV's in each plane. This configuration ensures that at any given at time and any given place on the Earth, five to eight satellites are in a direct line-of-sight from the user.

    Now, if one can provide a way for a ground receiver to synchronize its clock with the satellite clock, a simple measurement of the time delay in the signal received from a satellite in view of the Earthbound user, should result in a precise range to that satellite. Imagine for example a ground receiver which finds and locks onto one visible satellite, synchronizes its clock with the satellite clock, measures the time delay, computes the range, stores this number along with the reported position of the satellite, then locks onto a second visible satellite, and repeats this process until ranges and positions from three satellites have been obtained. This isn't how GPS works, but it's getting close!

    Before delving into a more accurate explanation of how GPS works, let's examine some nonrelativistic sources of error in the simple procedure I have just outlined. As I said, in principle, determining the range to each satellite is a matter of a simple computation: the time delay of each signal from the satellite, multiplied by the speed of light, gives the range! However, the signals are not in fact transmitted in along the geometric line of sight, because they are diffracted at the upper boundary of the ionosphere (at about 1000 km above the Earth's surface) and then again at the boundary between the ionosphere and the troposphere (at about 70 km above the Earth's surface). These boundary layers are move up and down, depending upon the time of day, the latitude, and other factors. Moreover, the lower 8-13 kilometers to the atomosphere are active participants in local weather conditions, and the speed of light in air is different from the speed of light in vacuo (and the temperature of the air matters!). In addition, satellites which are closer to the horizon will transmit signals which are subject to more atmospheric disturbance than those near the zenith. In sum, ionospheric, tropospheric, and local weather conditions can result in errors of ten meters or more. Furthemore, it is possible for the same signal to arrive at the receiver at different times, having taken multiple paths to get there; this can account for another half meter or so of inaccuracy. All these sources of error must be taken account of and corrected by the GPS system.

    Further "Newtonian" sources of error arise in determining the precise position of each satellite. In principle, a Keplerian orbit about the Earth is determined by six orbital parameters, usually taken to be the following:

    • the eccentricity of the elliptical orbit,
    • semi-major axis of the orbit,
    • the inclination of the orbital plane to the equatorial plane of the Earth,
    • the right ascension of the ascending node
    • the angular location of the perigee (point of closest approach),
    • the time at which the satellite passes the perigee

    ow, as I said, I have not yet described how GPS really works. There are two fundamental issues I have not addressed:

    * How does the ground receiver synchronize its (cheap, inaccurate) clock with the (highly accurate and expensive) atomic clocks carried aboard a given SV?
    * How do the SV's synchronize their atomic clocks with each other, and how is this collaborative timekeeping (called GPS time) converted by the receiver to the correct UTC for a given location on the ground?

    There is also a further component to the GPS system which I have not yet discussed. In addition to the satellites themselves, the space segment of the system, and the millions of hand held GPS receivers operated by people around the world, the user segment, there are also four unmanned ground stations (one located in Hawaii, a second on Kwajalein, an atoll in the Pacific Ocean; a third on Diego Garcia, an island in the Indian Ocean, and a fourth on Ascension Island in the Atlantic Ocean), which are devoted to carefully tracking the position of each GPS satellite, taking readings twice every three seconds. Each station automatically uses local weather and ionospheric conditions to average the tracking data, and every quarter hour, reports its best estimate of the position of each visible satellite to the master ground control station, which is located at Schriever AFB, Colorado Springs, CO. Here, the orbits and on-board clocks of each satellite can be adjusted if neccessary, using more sophisticated computer models (and bigger computers!) than can be carried on the SV's. This is the third component of GPS, the control segment.

    ...

    [At this point, Baez mentions a number of technical issues relating to signal frequencies of the satellites etc.]

    ...

    So, how can the ground receiver synchronize its clock with the satellite clock, in order to carry out the basic time delay computation outlined above? The answer is that it doesn't--- instead of sequentially locking onto and synchronizing clocks with four different satellites, as suggested above, the simplest (and cheapest) GPS receivers first lock onto the signal of one satellite, i.e. compare their internally generated C/A signal with the satellite signal until they get their own (cheap, inaccurate) clock in "roughly in synch" (modulo a still undetermined offset) with GPS time, and then records a reception time (by its own clock). It then locks onto the next signal, and repeats this process until four reception times (modulo undetermined offsets) have been recorded. Only then does it combine this data to determine the common offset of its clock from the satellite clocks, in effect resynchronizing its clock with three on-board atomic clocks. It then uses trilateralization and the declared position of each satellite as described above to determine the its own position. One way to think about this is that by locking onto four satellite signals, the receiver can determine its position and one more number, the offset of its clock from the highly stable, accurate, and mutually synchronized clocks carried by the satellites.

    The grand result is that SPS users can obtain their position accurate to within 100 meters (latitude and longitude), their altitude to within 150 meters, and the universal time to within 350 nanoseconds. PPS users can obtain their position accurate to within 20 meters, their altitude to within 30 meters, and the universal time to within 200 nanoseconds. Actually, even this is merely the tip of the iceberg--- more sophisticated users can use two or more sequential ground receivers, or a parallel receiver capable of locking onto several satellite signals at once, and can use various least squares estimations to collate the data collected in order to considerably improve on the stated accuracies, typically to a few meters in the position accuracy. Furthermore, stationary receivers (e.g. used by geologists to study the motion of tectonic plates, or volcanic terrain) currently achieve position accurracy on the order of one mm!

    ...

    [And now that you have a sense of how complicated the system is, we get to the relativity part]

    ...

    The first 10 GPS satellites, comprising Block I, were used for testing and for military geolocation, and were launched beginning in 1978. The next 24 satellites, comprising Block II, were launched between 1989 and 1994; these are the SV's used in the operational GPS system. The way in which Van Flandern's claims quoted above are misleading is now easily summarized:

    • It is true that the current (Block II) satellites carry clocks which are occasionally adjusted from the master ground control station.
    • It is completely false that the GPS somehow defies the predictions of relativity theory. Indeed, when the first atomic clock was sent into orbit in June 1977 (aboard a satellite which was a testbed for the Block I GPS), and I quote from Ashby's paper:

      there were some who doubted that relativistic effects were real. A frequency synthesizer was built into the satellite clock system so that after launch, if in fact the rate of the clock in its final orbit was that predicted by GR, then the synthesizer could be turned on bringing the clock to the coordinate rate necessary for operation. The atomic clock was first operated for about 20 days to measure its clock rate before turning on the synthesizer. The frequency measured during that interval was +442.5 parts in 10^12 faster than clocks on the ground; if left uncorrected this would have resulted in timing errors of about 38,000 nanoseconds per day. The difference between predicted and measured values of the frequency shift was only 3.97 parts in 10^12, well within the accuracy capabilities of the orbiting clock. This then gave about a 1% validation of the combined motional and gravitational shifts for a clock at 4.2 earth radii [the radius of the satellite's orbit].​
    • It is true that GPS is not used as a test of gtr, because it is simply not designed for that purpose. In particular, the orbiting clocks are occasionally reset from the ground to maintain the best possible synchrony of the orbiting clocks with one another and with UTC time.
    • It is completely false that the design of the GPS system ignores relativity theory. Relativistic effects in the GPS system are vitally important. The total difference in the rate of atomic clocks on board a GPS satellite and the reference clock at the USNO amounts to some 38,600 nanoseconds per day. (This is mostly due to a combination of the Sagnac effect for a clock which is moving wrt the GPS receiver, and the relative gravitational time dilation between a stationary clock on the Earth's surface and a stationary clock 20,200 km above the surface, as mentioned in the above quoted paragraph from Ashby's paper; frequency shifts in clocks on the ground wrt UTC due to inhomogeneties in the shape of the Earth also play a role.) In contrast, in order to maintain the accuracies listed above, the GPS system must maintain a timekeeping synchrony within 10 nanoseconds variation per day, indefinitely! The major way in which the 38,600 nanosecond per day discrepancy due to relativistic effects is accounted for is by building into the GPS software used to keep the satellite clocks in synch with each other and to synchronize GPS time with UTC an effective downward frequency shift of 446.47 parts per trillion in the orbiting atomic clocks. In addition to this basic conversion factor, GPS receivers are programmed to take account for the fact that slight eccentricities in the satellite orbits result in tiny periodic changes in the frequency of the orbiting clocks.

    At this point, I can do no better than send readers who have not already been there to Neil Ashby's paper for a detailed accounting of str and gtr effects which are significant in the GPS system. ... You can also try this paper by Charles W. Misner (Physics, University of Maryland), and this one by Clifford Will (Physics, Washington University). You can find additional references in the posts by Tom Roberts included in this collection.
     
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  3. superluminal I am MalcomR Valued Senior Member

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    James,

    Just a quick comment. I have previously read this article and most of the other ones you have posted. All excellent info.

    Is it not yet obvious that the denial of SRT by certain folks is rooted in their inability to accept the fact that the universe is not open to intuitive understanding at a certain level? And with that in mind, they will never accept SRT?

    MacM's problem is with time dilation. He makes a distinction between "mutual time dilation" and "reciprocity". I still would like to hear his distinction here.

    Geist is stuck on absolutes. His arguments have been shown,very nicely by BillyT, to be circular, based on the presupposition of a non-existent value Va (Cu = unicorn color???).

    I think the psychology of the interaction between the participants of this discussion is becoming far more interesting than the subject itself!
     
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  5. James R Just this guy, you know? Staff Member

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    superluminal:

    That's right, but I think there's more to it than that. It's a desire to cut down the tall poppies. Since they don't understand the theories they are attacking, they don't understand why they aren't achieving what they think they are achieving, either.

    The usual suspects around here couldn't put a mathematical proof (or refutation) together to save their own life.

    I also think that some crackpots feel left out of the "club", because they weren't bright enough to keep up, and are therefore disgruntled and want revenge. The best revenge would be to see all those supposedly bright people proved wrong and forced to eat their words.

    Er... that was me, actually, though Billy T has made some good points, too.

    I have experienced the various psychologies at play for a number years now on different parts of the internet. Not everybody is motivated as I have said above, but many are.

    I have occasionally come across people who really want to get an education and who are willing to learn things. But I would never class somebody as a crank who acknowledges that they don't know all the answers and is willing to revise their views in the light of explanation.
     
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  7. 2inquisitive The Devil is in the details Registered Senior Member

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    Great, James R, just great! I am so glad you have taken an interest in GPS and taken
    the time from your busy schedule to understand how it operates. I like your presentation and agree it is a very good representation of how GRS works. I know I
    will be able to learn from you, to help clear up a few questions on EM wave propogation that I have. I see GPS as an experiment that helps us decipher exactly
    what is happening to the signal as it encounters different effects that changes its
    frequency. I am not actually trying to find fault with ANY theory, just to compare
    theory with actual results to the best of my limited abilities. That is where a knowledgable physicist can be invaluable in helping everyone, including myself, understand situations where theory and results seem somewhat confusing to us
    less informed members. I only have a limited understanding of GPS, but I know enough
    to tell when someone claiming to understand the system really understands it or not.
    I can clearly see that you do understand it now, James R. This quote from you was one of the keys:
    (This is mostly due to a combination of the Sagnac effect for a clock which is moving wrt the GPS receiver, and the relative gravitational time dilation between a stationary clock on the Earth's surface and a stationary clock 20,200 km above the surface, as mentioned in the above quoted paragraph from Ashby's paper; frequency shifts in clocks on the ground wrt UTC due to inhomogeneties in the shape of the Earth also play a role.)"
    No challenges from me as I agree with what you have stated. My questions relate to
    the details of how the inhomogeneties in the gravitational potential of the Earth's
    geoid affect the signals, for instance. Do variations in gravitational potential over the
    Earth's surface affect the orbital altitude of the SV's, resulting in a distance calculation
    that must be compensated for, or does the slight variation in gravity affect the frequency of the transmitted signal, or both? I believe you were referring to Earth's
    obliqueness in your statement, but the density of the Earth (water or rock) under the
    satellite also has a small, but measurable, effect in the precision GPS applications, such as
    the study of tectonic plate movement and surveying. As always, I like details, heh!
     
  8. geistkiesel Valued Senior Member

    Messages:
    2,471
    Billy T is a creep, who is a praticed and systematic distorionist, a convoluted and contradictory logician, that has the manifest inability to say the same thing out of both sides of his mouth.

    Can you prove the "Va" reference you utter there SL old chap? Or did you borrow the term to have sopmething to trash by innuendo, casting dispersion on the system by the simple referebnce to a term that readers have no reference to. . . . , well you kniow hiow to this better than any SL . . rational thought you are unable tio unsderstand and even if yiou did understand it your position wouldn't change would it?

    And you SL what have you to offer to the discussion except your "1000 points iof light mantra" , I mean "1000 experiments that prove . . "
    I
    You can talk your psychological profiles all you want SL, and in the mean time try answering the following with some attempt to include some scientific content.

    Two photons are emitted moving oppositely to each other from the midpoint of clocks located along the trajectory of the photons. The clocks and emission devices located at physical midpoint of the sources of the photons. are moving to the right. Now as Pete tells me, indirectly, that an observer on the moving frame will see the midoint of the emitted photons moving with the frame at the frame velocity. This, says Pete is what the moving observer sees. Pete cant fathom the effect of the postulates of light, but who cares, Pete is a committed SRTist,depsite what he says. Pete doesn't know period.

    Can you grasp this SL? The photon moving to the left is obstructed in its trajectory by the clock that is moving to the right. Relative to the pont P, the emission point of the photons the left clock is moving with velocity v. The photon moves a distance ct abd the clock moves a distance vt wrt P.
    The right moving photon has moved a distance ct to the right wrt P. The right photon is 2vt short of the right clock when the left photon strikes the left clock.

    Is this an accurate description of what is occurring?
    I mean is the distance open to the left photlon the same as the distance avbailable to the right moving photon before the photons arrive at the clocks?
    From the point of emission the left photon will move a distance ct when striking the left clock.

    The right phjoton will move a distance ct + ct', where ct' = 2vt + vt' before striking the right clock. Now the postuilates of light tell us that the motion of light is independent of the motion of the source, the light moves at constant velocity c, the motion of llght isotropic. This means SL that what you speak is SRT silliness.
    Simply said. when the left and right photns have each moved a distance ct the left photn has reached the left clock while the right photon is still 2vt from the right vlock. The only way you keep SRT is to manipulate the motion of light by looking at it.

    I know that you and Pete agree that the observer sees the midpoint of the emiitted light moving with the observer.and hence the photon will arrive at the left and right clocks simultaneously, as if the frame were not moving.

    How do you unravel the governing influences of the three postulates of light I mentioned? How do let your observer report his silliness and grant him justification for assuming the midpoint oif the emitted light is moving at his velocity just because he perceives it that way? Even when his velocity is erronmeously perceived as at rest with respect to the embankment?

    I can understand the observer will become confused and take the physical midpoint for the actual invariant midpoint, but then SRT crumbles when you agree that the observer doesn't really have the powers to determine the laws of physics just because he perceibves things a certain way. You criticize classical analysts for accepting what they observe as flawed because the observation is coherent, logical, reasonable, in agreement with the laws of ophysics. Then you grant the ignorant observer the power of defining relauioty by what the observer "peceives." and more so whenh you emphsize thagt the perception ios "counter intuitive". Go figure.

    TYhis is indeed an interstingpsychiological stagte of mind. The taught loss of intuitive thought, the acceptance of the "not intuitively iobvious" the discarding iof aobservation, the loss of physical law the mouthing of postulates of light and the rude discarding of thaose postulates when convenient for the maintenace of SRT.

    You SRTists have bought onto irrational and unreasonable mental structures, but it is a tight knitg club, i must admit that.I do see that SL has devloped into the perfect SRT clone manfest by the sheer inability to talk in technical physical terms.
    Geitkiesel
     
  9. superluminal I am MalcomR Valued Senior Member

    Messages:
    10,876
    Ok Geist. This website (which I posted months ago) has what may be the best demonstration (IMO) of what is going on with spacetime frames, etc.

    http://casa.colorado.edu/~ajsh/sr/postulate.html

    Now. Geist. I comprehend your experiment 100% as I did when it was presented N months ago and probably long before that. It is exactly the same as the demonstration of Vermillion vs Cerulean at the center of their individual light cones. This is the solution to your light-source-in-the-middle of-a-moving-frame experiment. Simple huh?

    The crux of the matter is now this. Your analysis of the experiment assumes that there is no "skewing" of spacetime and the associated light cone and world-line of objects in different frames. If you assume that, then your analysis leads to the results that you see. How could it not?

    We all (SRTist's) accept the distortion of spacetime frames wrt other non-comoving frames. Do you grasp this? Therefore the solutions presented in the above website make perfect, bulletproof, sense to us.

    Ok. So, the postulates of special relativity were formulated to address some basic observations in the way-back. A key one being the MM null result (this and all subsequent verifications. If you refuse to accept these, then we may as well be talking religion. Pointless.). If the earth is moving and changing direction about it's own axis and in its orbit about the sun, and with its motion through the galaxy, and the galaxies motion through space, can we reasonably postulate that the earth is the non-moving reference for the whole universe?

    Of course not.

    Therefore, the interpretation of the MM null result must be this: If observers on a wildly moving planet measure the speed of light to be constant in all orientations, then all observers must measure the speed of light to be constant, otherwise you must endow the earth with some special status among all places in the universe. This would be absurd.

    Also, since the speed of light, which is featured in experimentally verified theories and equations that describe some of the most fundamental properties of the universe, is measured in all inertial frames to be c, then it is correct to state that "physics" in general will be the same regardless of your uniform motion. Right?

    So, without the resources to do our own precision experiments, we accept what hundreds of scientists have been doing for decades - testing the postulates of relativity. All of the implications of the postulates have been tested time and again. This is why I post sites showing research results. If you refuse to accept these results, then you are on your own. Your logic will make sense only to you and a handfull of others who reject test results obtained by the people qualified and financially endowed enough to get them - physicists.

    Remember, your logic makes sense if spacetime frames don't shift for different observers. We accept the evidence that they do shift. Ok?
     
  10. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    by superluminal:

    Therefore, the interpretation of the MM null result must be this: If observers on a wildly moving planet measure the speed of light to be constant in all orientations, then all observers must measure the speed of light to be constant, otherwise you must endow the earth with some special status among all places in the universe. This would be absurd.
    ============================================================

    Why do you keep implying M&M means anything other than what was shown? What was shown in the experiment was that the speed of light from a source co-moving with the
    receptor AND THE MEDIUM is constant. The medium is Earth's atmosphere. Conduct
    the M&M experiment completely under water. Do you not think the results would be
    the same, since there is no relative velocity between source and receptor/beamsplitter? From that simple experiment, you conclude the speed of light
    is constant between relatively moving observers throughout the universe, regardless of
    motion or location of the observers. The speed of light is not the same in water as it
    is in the atmosphere, it also varies in different regions of our atmosphere. M&M does
    NOTHING to support the postulate that the speed of light in a vacuum is invariant to all observers,
    regardless of motion of source or receptor. The speed of light is NOT measured in all
    inertial frames to be 'c'. It is only postulated to be 'c' in a vacuum. It has never been
    measured between relatively moving frames in a vacuum, let alone in all inertial frames.
    The postulate is an assumption, not a verified fact.
     
  11. superluminal I am MalcomR Valued Senior Member

    Messages:
    10,876
    2inq,

    First, here it is again for the umpteenth time:

    http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#one-way tests

    Please read all of the experiment descriptions. Everything you said in your last post was wrong. All experimental evidence using laboratory sources, terrestrial sources, extraterrestrial sources, moving objects, different media, vacuum, and the easter bunny, support an isotropic nature of light in all circumstances.

    Please tell me what you are missing from the experimental list from the site listed above.

    And of course, the results of isotropy will be the same in any medium. As for the speed, when we talk about "c" we mean in vacuum. That is a fundamental constant of nature. We all know it changes with the refractive index of different media.
     
  12. 2inquisitive The Devil is in the details Registered Senior Member

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    3,181
    For the umpteenth time, PICK AN EXPERIMENT, one experiment, which ACCURATELY
    MEASURED the speed of light within the vacuum of space between two relatively
    moving frames. Since you haven't picked any experiments, let me pick some. From
    your source above:
    "The Fizeau Experiment
    Fizeau measured the speed of light in moving mediums, most notably moving water. Fresnel proposed a "drag coefficient" which putatively described how strongly a moving material medium "dragged" the ether. SR predicts no ether but does predict that the speed of light in a moving medium differs from the speed in the medium at rest, by an amount consistent (to within experimental resolutions) with these experiments and with the Fresnel drag coefficient."
    The speed of light in a moving medium differs from the speed of light in a medium at rest. Did you know this, superluminal? Light is not invariant wrt a moving observer in
    a medium. As I have stated many times, I believe the vacuum of space is not 'empty',
    but is a field through which light propogates. Yes, light propogates through the field
    at 'c', but that 'c' is relative to the 'c' of an observer in a different gravitational field.
    Much the same as the speed of light is different in any medium, but can you measure
    that difference while you and your measuring equipment are immersed within the same
    medium? The difference only shows up when comparing one medium to a different
    medium, like air and water, or one gravitational field to another gravitational field of
    different gravitational potential.
    Can I pick another experiment? How about this one:
    "The research leading up to this finding consisted of an analysis of electromagnetic radiation data that has been compiled and published by several independent research groups since the 1980's. In our analysis, John Ralston and I studied polarization measurements of electromagnetic synchrotron radiation emitted by distant radio galaxies. Extensive, computer aided calculations indicates that this radiation exhibits an unconventional rotation of its polarization plane. The effect is small, and comes in addition to other known, conventional polarization rotation effects.

    The polarization rotation has the characteristic property that it depends systematically on the angle between the radiation's direction of travel and a fixed direction in space. This result indicates that electromagnetic interactions are anisotropic in nature. It defies the notion that, in electromagnetism, all spatial directions are equivalent.

    Our research has also focused on constructing a theoretical generalization of electrodynamics that incorporates anisotropy in a way consistent with the observed data. "
    http://www.cc.rochester.edu/college/rtc/Borge/aniso.html


    Here is where it was published:
    http://arxiv.org/abs/astro-ph/9704196
     
    Last edited: Jun 14, 2005
  13. superluminal I am MalcomR Valued Senior Member

    Messages:
    10,876
    2inq,

    This is bullshit. Polarization rotation can be affected by many things such as intergalactic dust and gas. Did they consider this?

    (EDIT: Looks like they did. Nevermind...)

    Now,

    Wrong. Prove otherwise. Your beliefs are not consistent with observations. Check the experiments involving binary pulsars:

    Here are a set of moving sources, in space. What's the problem? Light is isotropic. Get used to it.
     
    Last edited: Jun 14, 2005
  14. superluminal I am MalcomR Valued Senior Member

    Messages:
    10,876
    http://redshift.vif.com/JournalFiles/V08NO3PDF/V08N3WOL.PDF
     
  15. James R Just this guy, you know? Staff Member

    Messages:
    39,397
    Can we please keep this thread for discussions of the GPS system?

    Thankyou.
     
  16. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    I don't see where I have said the velocity of light was source-dependent, do you?
    Just the opposite, I said the velocity of light was dependent upon the medium. What do you measure when you measure the speed of light in water, for instance? Does
    the speed of light in water depend on whether the light entered the water from the air
    or through a boundry of glass? Doesn't matter, the speed of light in water is not affected by the medium it traveled through before. The light would have to speed up
    if the transition were from glass-to-water and slow down if the transition were from
    air-to-water to give a consistent speed in the water. Same as when light enters our
    atmosphere, it has to slow according to the state of the atmosphere it is travelling through. Now, what happens when light from the surface is projected up through the
    atmosphere? It has to increase its velocity when entering the vacuum field. The speed
    of light is regulated by the medium through which it is travelling, not source or receptor. What do you believe regulates the speed of light to 'c' in a vacuum, superluminal? Yes, I know the permeability and permittivity of the vacuum. Does that
    not describe a field to you?
    Sorry, did you notice the title of this thread that James R started? I will not be distract
    by off topic posts again, I hope, hehe!
     
  17. James R Just this guy, you know? Staff Member

    Messages:
    39,397
    2inquisitive:

    I am not an expert, but I think probably both, in effect. The frequency difference would be minimal, I think, but the small shift in time dilation due to having a bit more or a bit less mass underneath the satellite is apparently significant enough to need compensation.

    Yes, that's completely correct. If the satellite is over Mount Everest, the time dilation will be slightly different to when it's over the Pacific Ocean, for example.
     
  18. superluminal I am MalcomR Valued Senior Member

    Messages:
    10,876
    Aye, captain.
     
  19. 2inquisitive The Devil is in the details Registered Senior Member

    Messages:
    3,181
    Thanks for your comments, James R. I'm happy to learn I didn't misinterpret GPS, and
    other satellite data, too much. At least, so far. Now, something a little more controversial. It seems to me (can't state it as a fact) that EM propogation SPEED is
    affected by gravitational potential it is travelling through. I mean 'c' is always measured as a constant by an observer within a certain potential, but when this
    measurement is compared directly with an observer's measurement in a different
    gravitational potential, a relative difference could be found. The clocks tick differently
    in different potentials. If a metal meter stick, measured by the speed of light in one
    location, is moved to a location with a lower gravitational potential, will the meter
    stick change length in its own frame of reference to make up for the faster clock, or
    will the meter stick remain the same length and the speed of light change slightly to
    continue to travel one meter in 1/299,792,458 of the faster second in the new gravitational potential? I realize this is not STR because gravity is the mechanism of
    change in clock beats, but which do you think may happen? Or am I making some
    fundamental error in my example? The changing frequencies of GPS clocks and signals
    is where I, uhh, deduced my example. Hope it is not off topic.
     
  20. MacM Registered Senior Member

    Messages:
    10,104
    Now this really takes the cake.

    I post a simple question 2 - 3 times and you continue to ignore it and run off and post this garbage. I'll repeat my question after I correct your extremely distorted record.

    1 - Why on earth would you quote John Baez's view of GPS. He has no specialty in that field. Your only reason is because he is a relativists. Many relativist, and simply ignorant people, mis-state the facts and claim SRT is used by or proven by GPS.

    John Baez
    http://andrej.com/mathematicians/B/Baez_John.html
    http://math.ucr.edu/home/baez/README.html

    2 - I have never once quoted Tom V. F. and I base none of my views on his work.

    3 - I have repeatedly referanced Ronald Hatch a world recognized, honored and distinguished specialist in the GPS field.

    Ronald Hatch
    http://www.ion.org/awards/dsaward2001.cfm
    http://www.egtphysics.net/scandclock.pdf

    Please all note page (4) 2nd paragraph, where he states the velocity affect on clocks is an energy function. I too have argued that possibility. Note also his Conclusions about SRT and GPS.

    4 - I have also repeatedly referanced Niel Ashby. He is also good but not as experienced in the GPS field. He does more in the theoretical explanations but even he is careful to refer to GR and velocity compensation or relavistic adjustments and not harp about SRT perse.

    Niel Ashby
    http://www.colorado.edu/physics/Web/directory/faculty/ashby_n.html
    http://www.leapsecond.com/history/Ashby-Relativity.htm

    Finally everyone should be aware of what Hafele of the H&K Atomic Clock Tests had to say to the US Government In Secret before they massaged the data to claim they had proven Einstein's Time Dilation.

    ************** Extract from following Link ********************

    http://www.electromagnetism.demon.co.uk/16133.htm

    "Most people (myself included) would be reluctant to agree that the time
    gained by any one of these clocks is indicative of anything .... the
    difference between theory and experiment is disturbing."

    - Hafele, Secret United States Naval Observatory internal report, 1971.

    Obtained by A G Kelly two decades later under the Freedom of Information
    Act.
    **********************************************************

    Your lead referring to me as a well known crank would be an insult if it were not for the fact that it is totally without foundation and is frequently used by you and others in an effort to demean what I say without addressing the issue. In the final analysis it is the issue which demonstrates which of us has the better grip on reality.

    Now for the fourth time:

    "A" and "B" are two clocks with a relative velocity of 0.866c. What is the gamma function between these clocks according to SRT?

    You are such a non-crank smart ass and know so damn much about
    GPS and relativity, surely you can answer this question.

    PS: Your good friend Yuriy the physicist is listed on Crank.Net. He agreed with you on GPS and relativity. Wonder what we should gather from that?

    PSS: If you want to know the truth I am starting to enjoy this. Your repeated personal attacks on me can mean nothing other than you are scared shitless that what I am presenting is starting to gain traction and you have no valid responses.

    PSSS: If you claim you do then please post ONE case of SRT reciprocity that has been observed and/or data recorded.
     
    Last edited: Jun 14, 2005
  21. energy1 Registered Member

    Messages:
    22
    Well, that is a true statement, and a good deduction on your part, 2inquis. Its well known experimentally that there is a time delay for EM radiation going through a gravity field, (as measured by someone outside of the field). Its called the Shapiro time delay; and has been exper. verified a number of times, usually by bouncing microwaves off Mars or Venus in superior solar conjuctions where the beam passes very close to the solar surface; (and also bouncing off Voyager spacecraft through the solar field). And, as you say, it is expected (by GR) that within the gravitational field there is no 'local' variation in c.

    Please Register or Log in to view the hidden image!



    However, I should say this is an extremely small effect, and only becomes measureable due to 1). the time accumulation over such long distances ( >100 million miles), and 2). due to the very high gravitational potential of the sun. (I think a GR explanation would say it is equivalent to the lengthening of the path due to the bending of light in the solar gravitational field).

    I could be mistaken but I believe the effect would be totally undetecable in a terrestrial environment even with extremely accurate cesium clocks.
    IOW, this effect should be way below the limits of GPS accuracies. Its simply a matter of the magnitude of the effect.

    I haven't been following closely here so I'm not sure how these details will affect your arguments.

    Energy
     
    Last edited: Jun 14, 2005
  22. MacM Registered Senior Member

    Messages:
    10,104
    It is interesting how you can assert MacM has a problem. It is not I that have a problem.

    The problem would be for anyone that doesn't understand the differance between "Mutual Dilation" and "Reciprocity" to even have comments about the theory, much less berate those that point out these inconsistancies in SRT.
     
  23. James R Just this guy, you know? Staff Member

    Messages:
    39,397
    MacM:

    Interesting that you don't comment on the content of my first post at all, but concentrate on argument by authority.

    Baez is an excellent physicist, and very knowledgable about relativity - much moreso than me, I'll wager.

    I've read a lot of his stuff, and it's all good.

    Strange that your views are so close to his, then.

    Fair enough.

    It's hard to tell whether he has a good point in his paper, without examining it in detail. The argument is complex, and probably wrong. It doesn't match up with your simplistic arguments, in any case.

    There's only one source for the statement you so love to quote, which is rather dodgy if you ask me. Anyway, relativity doesn't hinge on the result of one experiment, as you would have us believe.

    I have no intention of going off on this tangent in this thread. I've already replied several times to you regarding this in another thread. Read those replies.

    First, Yuriy is not my "good friend". Whatever gave you that idea? I don't even know him.

    Secondly, he is listed for one specific thing on crank.net. That doesn't mean he is cranky on everything, or even on the thing he is listed for, necessarily. That's just somebody's opinion. You have a listing there, too, of course, don't you? I guess that makes you at least as cranky as Yuriy, right?

    Yawn.

    In which reference frame?
     

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