Einstein's Relativity and Everyday Life -- Clifford M. Will

Discussion in 'General GPS Discussion' started by Sam Wormley, Jun 5, 2006.

  1. Sam Wormley

    Sam Wormley Guest

    Einstein's Relativity and Everyday Life -- Clifford M. Will


    Einstein's Relativity and Everyday Life
    Clifford M. Will

    What good is fundamental physics to the person on the street?

    This is the perennial question posed to physicists by their non-science
    friends, by students in the humanities and social sciences, and by
    politicians looking to justify spending tax dollars on basic science.
    One of the problems is that it is hard to predict definitely what the
    payback of basic physics will be, though few dispute that physics is
    somehow "good."

    Physicists have become adept at finding good examples of the long-term
    benefit of basic physics: the quantum theory of solids leading to
    semiconductors and computer chips, nuclear magnetic resonance leading
    to MRI imaging, particle accelerators leading to beams for cancer
    treatment. But what about Einstein's theories of special and general
    relativity? One could hardly imagine a branch of fundamental physics
    less likely to have practical consequences. But strangely enough,
    relativity plays a key role in a multi-billion dollar growth industry
    centered around the Global Positioning System (GPS).

    When Einstein finalized his theory of gravity and curved spacetime in
    November 1915, ending a quest which he began with his 1905 special
    relativity, he had little concern for practical or observable
    consequences. He was unimpressed when measurements of the bending of
    starlight in 1919 confirmed his theory. Even today, general relativity
    plays its main role in the astronomical domain, with its black holes,
    gravity waves and cosmic big bangs, or in the domain of the
    ultra-small, where theorists look to unify general relativity with the
    other interactions, using exotic concepts such as strings and branes.

    But GPS is an exception. Built at a cost of over $10 billion mainly for
    military navigation, GPS has rapidly transformed itself into a thriving
    commercial industry. The system is based on an array of 24 satellites
    orbiting the earth, each carrying a precise atomic clock. Using a
    hand-held GPS receiver which detects radio emissions from any of the
    satellites which happen to be overhead, users of even moderately priced
    devices can determine latitude, longitude and altitude to an accuracy
    which can currently reach 15 meters, and local time to 50 billionths of
    a second. Apart from the obvious military uses, GPS is finding
    applications in airplane navigation, oil exploration, wilderness
    recreation, bridge construction, sailing, and interstate trucking, to
    name just a few. Even Hollywood has met GPS, recently pitting James
    Bond in "Tomorrow Never Dies" against an evil genius who was inserting
    deliberate errors into the GPS system and sending British ships into
    harm's way.

    But in a relativistic world, things are not simple. The satellite
    clocks are moving at 14,000 km/hr in orbits that circle the Earth twice
    per day, much faster than clocks on the surface of the Earth, and
    Einstein's theory of special relativity says that rapidly moving clocks
    tick more slowly, by about seven microseconds (millionths of a second)
    per day.

    Also, the orbiting clocks are 20,000 km above the Earth, and experience
    gravity that is four times weaker than that on the ground. Einstein's
    general relativity theory says that gravity curves space and time,
    resulting in a tendency for the orbiting clocks to tick slightly
    faster, by about 45 microseconds per day. The net result is that time
    on a GPS satellite clock advances faster than a clock on the ground by
    about 38 microseconds per day.

    To determine its location, the GPS receiver uses the time at which each
    signal from a satellite was emitted, as determined by the on-board
    atomic clock and encoded into the signal, together the with speed of
    light, to calculate the distance between itself and the satellites it
    communicated with. The orbit of each satellite is known accurately.
    Given enough satellites, it is a simple problem in Euclidean geometry
    to compute the receiver's precise location, both in space and time. To
    achieve a navigation accuracy of 15 meters, time throughout the GPS
    system must be known to an accuracy of 50 nanoseconds, which simply
    corresponds to the time required for light to travel 15 meters.

    But at 38 microseconds per day, the relativistic offset in the rates of
    the satellite clocks is so large that, if left uncompensated, it would
    cause navigational errors that accumulate faster than 10 km per day!
    GPS accounts for relativity by electronically adjusting the rates of
    the satellite clocks, and by building mathematical corrections into the
    computer chips which solve for the user's location. Without the proper
    application of relativity, GPS would fail in its navigational functions
    within about 2 minutes.

    So the next time your plane approaches an airport in bad weather, and
    you just happen to be wondering "what good is basic physics?", think
    about Einstein and the GPS tracker in the cockpit, helping the pilots
    guide you to a safe landing.


    Clifford M. Will is Professor and Chair of Physics at Washington
    University in St. Louis, and is the author of Was Einstein Right? In
    1986 he chaired a study for the Air Force to find out if they were
    handling relativity properly in GPS. They were.
    Sam Wormley, Jun 5, 2006
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  2. Sam Wormley

    Bhanwara Guest

    And apparently a master and skilled BS'er too.

    1) GPS corrections do not actually use the relativistic computations,
    they just re-synchronize. GR says "you have a mismatch,
    as would have any another system which would have computed
    the time required for light to travel the distance.

    2) There is indeed a difference between GR, and any non-GR system
    used to compute the time required for light to travel the distance.
    But this difference is much smaller than the 38 microseconds,
    and cannot be discovered at this scale.

    Basically, instead of using GR, one could have divided the
    distance by the speed of light to arrive at the time difference.
    That works, too.
    Bhanwara, Jun 5, 2006
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  3. Sam Wormley

    dda1 Guest

    I told you, Mukes Prasad, eating your own shit on a daily basis makes
    you mad (in addition to your being born a cretin). See here, how GPS
    really works, fuckhead:


    Do your parents know? Are your children retarded? Of course!
    dda1, Jun 5, 2006
  4. Sam Wormley

    Sam Wormley Guest

    Ignorance is bliss!
    Sam Wormley, Jun 5, 2006

  5. No, apparently not. I know Dr. Will personally. He has to be one of the
    straightest, least tolerant of any kind of BS man I've ever known. Read
    his book. It's an easy read, marvelously written. You can see his dry,
    to the point, matter of fact approach to problems from the way he
    Randy M. Dumse, Jun 5, 2006
  6. Sam Wormley

    Sue... Guest

    What planet are you from? Even the steward of a nukular
    arseinall isn't choosen on merit. I'ts about *marketing*.


    Sue..., Jun 5, 2006
  7. What an argument for top posting
    Robert Boucher, Jun 5, 2006
  8. Sam Wormley

    The Sorcerer Guest

    | What an argument for top posting
    The Sorcerer, Jun 5, 2006
  9. Sam Wormley

    Tom Roberts Guest

    The 38 microsec per day drift of a standard clock in GPS orbit was
    _measured_ during the initial setup of the first satellite. If, as you
    claim, this correction was to be applied by simply "re-synchronizing"
    the clocks, then in order to meet the accuracy specification of 3
    meters, the clocks would need to be "re-synchronized" 3,800 times per
    day, or almost 3 times every minute. Needless to say, a system based on
    such frequent "re-synchronization" could not possibly work. And indeed,
    the actual system uses corrections applied typically daily, and these
    corrections are MUCH smaller than 38 microsec (because the basic 38
    microsec per day is programmed into the satellites).

    That is not the problem. The problem is that standard clocks located in
    the satellites drift by ~38 microsec per day relative to standard clocks
    on earth.

    Hmmm. The "distance' is what one wants to determine, because the GPS is
    a _geo-location_ system. Basically the satellites repeatedly broadcast
    their position and time, and the receivers use that information from 4
    or more satellites to determine their location on earth. You seem to be
    singularly ignorant of what the GPS is, why it was built, and how it
    works. Perhaps you should actually _LEARN_ something about it before
    attem[pting to discuss it.

    Besides, what you claim simply does not work when the clocks in orbit do
    not remain in synchronization with clocks on the ground.

    Neither. The _physical_ correction to tick rate is applied to the
    satellite clocks, and that keeps them _approximately_ in synch with
    earth clocks and each other. Due to uncontrollable variations, small
    corrections are uploaded to the satellites daily; these are typically a
    few nanoseconds, or about 0.1% of the GR correction.

    Your reading ability as as poor as your understanding of the GPS. Plain
    and simple: the GR correction is built into the satellites. <shrug>

    Tom Roberts
    Tom Roberts, Jun 6, 2006
  10. Sam Wormley

    Bhanwara Guest

    What you are saying COULD be right -- but your post is a basic
    repetition of published facts. Since relativity is heavily political
    and opposing viewpoints do not get equal press, therefore
    it is equally possible that there are facts that have not
    been published. In fact, it is highly possible.

    Furthermore, all theoretical considerations indicate that
    what you are saying should not be right. A theory resulting from
    random mathematical manipulation with no insight behind it
    just shouldn't describe reality, as it would be the wildest of
    coincidences . Therefore, in lack of open debates on the matter,
    it is at the very least very doubtful.
    Bhanwara, Jun 6, 2006
  11. Sam Wormley

    Bhanwara Guest

    In addition to "random mathematical manipulation", also
    note, theories resulting from failure to understand
    how an em wave could propagate in empty space. It is hard
    to see how theories built upon a failure to understand
    something, and upon random insightless mathematical
    manipulation, can describe reality. It is much easier
    to see how they can become political snowballs,
    and generate false but extremely complicated defenses.
    Bhanwara, Jun 6, 2006
  12. Sam Wormley

    Mike Guest

    You can find the correction factor by trial-and-error in a trivial way.
    GPS clocks are corrected just once before lift-off and that is all.

    [snip remaining crap]

    Is there another application of GR? Even the cats in the streets are
    starting getting tired of this apologetic talk about GPS and such.

    By the way, INS (inertial navigation system) worked in 747's long
    before GPS and did the job as well.

    SR/GR - hahahahahahahahahahahaha - Falsified over ten times

    Mike, Jun 6, 2006
  13. Sam Wormley

    Sam Wormley Guest

    I don't think there is anything political about relativity.
    Nor is there any lack of published results. NASA, NSF and
    other sources still fund basic scientific research including
    relativity. Its biggest application, GPS is $30B+ industry,
    applying relativity to create a global infrastructure benefiting
    people all over the world.
    Sam Wormley, Jun 6, 2006
  14. Sam Wormley

    Sam Wormley Guest

    Certainly some corrections could have been determined by trial and error,
    but relativity theory predicted the degree of correction and explains
    it cause! Relativity correction were designed into the engineering,
    not added "just once before lift-off",

    See: http://edu-observatory.org/gps/gps_books.html
    Sam Wormley, Jun 6, 2006
  15. Sam Wormley

    Bhanwara Guest

    No, there is no lack of published research. But
    all published research *must* support relativity
    in order to get published.

    There have been reports that papers were refused publication
    because they were seen as implying something against relativity.

    That's not open, honest, inquiry. Honest researchers
    would get all research widely published and openly
    debated, and see where it leads. Prior suppression
    and filtering, is nothing but cheating.

    So after it's been established clearly that a certain segment of
    the researchers routinely cheat in their behavior, you are asking
    for a lot of unwarranted trust, in taking it at faith that all the
    details have been published honestly where the same segment
    of the researchers is concerned.
    Bhanwara, Jun 6, 2006
  16. Sam Wormley

    oldpal Guest

    See what you started!

    How do you figure the gravitational force is four times weaker at
    20,000 km above the surface of the earth?
    oldpal, Jun 6, 2006
  17. One can but admire this reasoning. :)

    Paul B. Andersen, Jun 6, 2006
  18. Sam Wormley

    dda1 Guest

    No , cocksucker . The correct statement is : Failure for the cretin
    Mukesh Prasad to understand how em propagates in empty space (and
    failure to understand everything elese in physics).
    What did you graduate in? Cock sucking?
    dda1, Jun 6, 2006
  19. Sam Wormley

    dda1 Guest

    Where did you get that , idiot Mukesh Prasad?
    Because they were incorrect, refutable by prior experiment, shithead
    Mukesh Prasad
    Why, some of you cretin "papers" got rejected, Mukesh Prasad?

    They don't cheat. You try to and you get exposed every time, asshole!
    dda1, Jun 6, 2006
  20. Sam Wormley

    SamSez Guest

    [next time you line your hat, use a little more tinfoil...]
    SamSez, Jun 6, 2006
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