in reply to Re^13: Converting GPS seconds to readable time&date (relativity)
in thread Converting GPS seconds to readable time&date

Well its way beyond me, but this experiment seems to explain it to me clock times going East vs. West So I'm guessing the GPS satellites are travelling either E or W, to remain at a constant point above the ground point, and as the plane experiment shows, the clocks will be different. Beyond that, I'm not going to think about it anymore, it's blowing my mind. :-)
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  • Comment on Re^14: Converting GPS seconds to readable time&date (relativity)

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Re^15: Converting GPS seconds to readable time&date (relativity)
by BrowserUk (Patriarch) on Jan 12, 2009 at 18:50 UTC

    One mistake that I (and others I think) made, is in thinking that GPS satalittes are goestationary. They're actually in Medium Earth Orbit (20200k) and orbit the earth every 11h 58m. They're also run at an inclination of 55 degrees, so that adds another relative motion.

    To my mind, the most amazing bit about relativity is not the math (which I have to take as read), nor the apparent paradoxes it produces; it's how anyone ever came up with the notion in the first place.

    Conceptually, it's right up there with the blind French mathematician, Bernard Morin who proved (topologically), that you can turn a hollow sphere inside out without breaking or creasing the surface.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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      As this thread has run so far into off-topic land already, there is a really good video that introduces the topology needed and then the steps taken in the proof: Turning A Sphere Inside Out (20 educative minutes)

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        Hm. 20 minutes at say 5MB per minute ~100MB. With my connection that's about 8 hours of download time (I couldn't hack the link to get a better estimate.)

        For now, I'll live with knowing that it's "possible"; that the math will remain forever beyond me; and that to date, no one seems to have found a practical application for it.

        And I'll save the video for "Real Soon Now" (if my TelCo ever fulfills its promise), for when I get broadband.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

      and orbit the earth every 11h 58m.

      It takes 24 hours for a person to orbit the center of the earth, so while the speed I gave was off, the satellites are still faster.

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        According to this they circulate the Earth at 3.9 km per second. But that's deceptive because its the relative speed of the observer that is crucial.

        And that waxes and wains like the tides, and oscillates sinusoidally at twice its orbit frequency, with its progression around the orbit. And then there's that it is moving in an orbit relative to a point that is moving in a smaller orbit, so a bit like spirograph if you ever saw the toy.

        Now we know why all the relativity examples use straight line motion away and back from a distant point :)

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

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