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Frame-dragging question

  1. Jun 21, 2006 #1
    I heard that some kind of experiment on frame-dragging was in process (or is that finished?). What was the outcome? Was the theory of Relativity vindicated? Does anyone know... wiki isn't very clear on this and it's full of math I can't even begin to imagine to understand... oh yeah also apparently wiki needs someone with expertise to improve that page (as a lay person I had alot of trouble understanding what the heck was going on).

    Oh yeah and here is the link just in case anyone wants to fix it up http://en.wikipedia.org/wiki/Frame_dragging

    PS. Sorry if I posted in the wrong forum... I think I did :S
     
  2. jcsd
  3. Jun 21, 2006 #2

    pervect

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    I gather from some discussion pages that those "needs attention by an expert" remarks are mainly Chris Hillman's "Things to do" list.

    [add]
    See for instance

    http://en.wikipedia.org/wiki/User:Hillman/Wikiproject_GTR_draft
    http://en.wikipedia.org/wiki/User:Hillman/WikiProject_GTR/Tasks


    There probably is a need for a less technical but still accurate page to describe frame dragging. I would suggest that you utilize the wiki "talk page" to address your concerns, I'm sure that there are a lot of people in a similar boat. CH is certianly doing something valuable by trying to provide graduate level input into the Wikipedia pages. There is not currently anyone I'm aware of who is "looking out" for readers without a graduate level degree.

    Anway, there is an experiment that has been done on Frame dragging, it is known as "Gravity probe B".

    The data has all been taken, however the results have not yet been published.

    You might find

    http://einstein.stanford.edu/

    helpful. The main page is a discussion of the status of the experiment, but they also have some explanations of how the experiment works and what it is trying to measure.

    On the extreme high end of the comprehnsibility scale (and the extreme low end of the technical accuracy scale) for frame dragging there is:

    http://einstein.stanford.edu/content/education/EducatorsGuide/Page28.html

    To give a rough idea, here is a quote from the page as to what's needed to carry out the proposed activity:

     
    Last edited: Jun 21, 2006
  4. Jun 21, 2006 #3
    We are awaiting the results of the experiments conducted by Gravity Probe-B. The results will take another year or so in terms of getting digested and published.
     
  5. Jun 22, 2006 #4
    Which was dissapointing to me.
    With their understanding of the experiment, the researchers could have easily said whether the incoming results were in agreement with GR. This was a year ago. They just insist on sticking to tradition. I remember some comment on their site defending this conservative stance at the time.
     
  6. Jun 22, 2006 #5

    Garth

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    As one with a vested interest in the result, who is seeking a non-"traditional" (i.e. non-GR) result on the geodetic N-S precession measurement, I take exception to your insinuation. You might be interested in the thread Alternative theories being tested by Gravity Probe B.

    It may be frustrating to have to wait so long, but the experiment was very complicated with many different factors that might affect the result being assessed as accurately as possible to make that result as precise as possible. I am sure the accuracy and unambiguity thus obtained will make the wait worthwhile.

    From the GP-B website
    April 2007 should do it.

    Garth
     
    Last edited: Jun 22, 2006
  7. Jun 22, 2006 #6
    Thanks for your replies guys :)... can't wait till 2007
     
  8. Aug 1, 2006 #7
    With regards to the Wiki article there is a section about velocity frame dragging:

    No references are given.

    What is velocity frame dragging?
     
  9. Aug 1, 2006 #8

    pervect

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    I am not positive, but I would suspect that the author is talking about the apparent rotation of the fixed stars when something massive "whizzes by" them at a large velocity - or, alternatively, the same rotation as observed by someone quickly flying past a large mass.

    Basically, if you fix a telescope on a guide star, and a massive body "whizzes by", after the body passses the telescope won't be pointing at the guide star anymore, it will have rotated - even if care is taken to design the telescope such that there are no tidal torques on it.

    This is true even if the telescope has no angular momentum.

    I ran across this effect while working on another problem. I'm not sure what the literature has to say about it, unfortunately - it's not clear what to search for, even if I had better access to the literature.

    The most controversial thing I can think of offhand is that one might argue that the effect as described could be predicted from SR by treating gravity as a force as a result of Thomas precession.

    The effect is rather similar to the geodetic or "De-sitter' precession that one gets in an orbit around a non-spinning test body. (Google for more info - there are a lot of hits. My statements are based on

    http://en.wikipedia.org/wiki/Frame_...agihara_observers_in_the_Schwarzschild_vacuum

    which may not be the easiest thing to understand).

    The major difference is that the orbit in this case is not circular, it is a "flyby" orbit.

    Geodetic precession is one of the things that is going to be measured by gravity probe B. It is somewhat interesting in its own right, but perhaps not as interesting as the Lense-Thiring precession, which is due to the actual rotation of the Earth, and the gravitomagnetic field caused by that rotation.

    Note that the reason GP-B is in a polar orbit is so that the geodetic precession effects will occur at right angles to the Lense-Thirring precession.
     
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