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  1. #1
    Sam Wormley's Avatar
    Sam Wormley Guest

    Default Time Too Good to Be True



    Time Too Good to Be True
    http://www.physicstoday.org/vol-59/iss-3/p10.html

    Without wishing to cause unnecessary distress, I would like to call
    attention to a couple of issues concerning time. The first is merely
    calendraic but the second concerns the future of time itself.

    The first issue is that we may have to say farewell to leap seconds.
    Leap seconds, as you might recall, are the occasional one-second
    adjustments of our clocks that are made to maintain harmony between
    the astronomical and atomic time scales. Personally, I would be sorry
    to see leap seconds go because that would cost me the pleasure of
    mulling over the best way to spend my next one. Although a mere
    second might seem to be too short to cause jubilation, I believe any
    gift of time deserves to be treasured. Also, one second is not really
    that short. It is long enough to record a few million high-energy
    scattering events, and in femtosecond physics, one second is
    virtually an eternity. Also, one second is sufficient for a word or
    quick kiss that might change your life.

    See: http://www.physicstoday.org/vol-59/iss-3/p10.html


  2. #2
    Richard Owlett's Avatar
    Richard Owlett Guest

    Default Time Too Good to Be True

    Sam Wormley wrote:


    I do not know what to say.
    That page was fascinating reading.
    Doubt I grokked 10% of its implications.
    thank you.


  3. #3
    Ben Rudiak-Gould's Avatar
    Ben Rudiak-Gould Guest

    Default Time Too Good to Be True

    Sam Wormley wrote:

    Leap seconds are slowly killing us. Every leap second they introduce makes
    the exact time of your death fall one second earlier. Man, I wish I'd been
    around during the switch from the Julian to the Gregorian calendar. Ten
    whole extra days of life! I don't understand those people who thought they'd
    lost ten days.

    -- Ben

  4. #4
    kashe@sonic.net's Avatar
    kashe@sonic.net Guest

    Default Time Too Good to Be True

    On Sun, 19 Mar 2006 19:49:59 GMT, Sam Wormley <swormley1@mchsi.com>
    wrote:


    I'll second that.

  5. #5
    Mike Jr.'s Avatar
    Mike Jr. Guest

    Default Time Too Good to Be True


    Sam Wormley wrote:

    First, cool article.

    Second, the discussion boils down to the concept of average
    signal-to-noise ratio. Beyond a certain precision, the signal will be
    swamped by the noise created by the various factors cited;
    gravitational blue shift, tidal oscillations, plate tectonic motions,
    compression/decompression of the earth's crust due to the affects of
    water (e.g. Amazon basin) and glacial retreat/advance. EE's deal with
    SNR all the time.

    --Best regards,
    --Mike Jr.


  6. #6
    Sam Wormley's Avatar
    Sam Wormley Guest

    Default Time Too Good to Be True

    Mike Jr. wrote:

    Once the clocks becomes the "lowest noise" standard reference, then
    the other observables, i.e., Geoid, altitude, horizontal shift, etc.
    can be deduced from the clocks.


  7. #7
    Martin Hogbin's Avatar
    Martin Hogbin Guest

    Default Time Too Good to Be True


    "Mike Jr." <n00spam@comcast.net> wrote in message news:1142855032.048462.128660@z34g2000cwc.googlegr oups.com...

    The problem described is more fundamental than that. In relativity
    proper time is different for every worldline. In other words every
    object has its own 'personal' time. There is no such thing as a
    'real' or universal time. With current clock accuracy we need to
    take relativity into account for things like the GPS system but it
    is still possible to define a universal time (UTC or IAT for example)
    that is valid for people on the Earth's surface. For all practical
    and measurable purposes there is still therefore the concept of
    'what time is it?'. The article pointed out that as we consider this
    question in greater accuracy that question ceases to have any
    meaning. Theoretical physicists have known this for years but
    soon it may have practical significance.

    Martin Hogbin




  8. #8
    Mike Jr.'s Avatar
    Mike Jr. Guest

    Default Time Too Good to Be True


    Martin Hogbin wrote:

    Martin,
    If your atomic clock was in deep space, far from any perturbing
    matter, you could push the accurracy much further. But the earth is a
    pretty noisy place.

    Even in deep space you would have to come up against a limit. How far
    down could you push it?

    To your point about UTC vs. individual world lines you should, in
    principle, be able to compute coordinate transformations bewteen any
    two such world lines. Sort of an adjustable UTC.

    --Mike Jr.


  9. #9
    Mike Jr.'s Avatar
    Mike Jr. Guest

    Default Time Too Good to Be True

    Sam,
    GPS is designed to do this now. The positions of the monitoring
    stations are very well known. So at the MS you measure your position
    and compute an error. This allows you to reverse engineer the bird's
    position. GPS has to model the geoid very closely. The Geoid is
    factored into the Kalman-Filter's ephemeris predictions.

    To your point, when the clocks hit their lower limit, we will be able
    to do this with more accuracy.

    BTW, I wonder what technology will replace atomic clocks ....

    --Mike Jr.


  10. #10
    Sam Wormley's Avatar
    Sam Wormley Guest

    Default Time Too Good to Be True

    Mike Jr. wrote:

    Light clocks...

 

 
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