How important to geometric theories is the GPB confirmation of the geodetic effect?

Discussion in 'Physics & Math' started by brucep, Jul 29, 2012.

  1. brucep Valued Senior Member

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    How important is the Gravity Probe B confirmation of the geodetic effect? My amateur opinion is it's very important for geometric theory. Any theory which describes spacetime using dimensions of space and time. No mater how many dimensions. I think it might 'round file' theory based on other stuff, like aether theories which allow for the detection of the aether or aether theories where the aether isn't detectable like Lorentz ether theory. I could be missing something in my amateur analysis?
     
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  3. OnlyMe Valued Senior Member

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    The GP-B data confirms predictions of GR, which is a geometric description of the relationship and interaction of objects, we experience and observe as gravitation. In that respect it is another confirmation.

    There are some relativistic ether models. I don't think any have been successful in duplicating the success of GR, but then neither has any attempt to develope a model of quantum gravity.

    One of the big problems that aether — ether theories carries with it is preconceived deffinitions. If one discards the fixed historical definition, there are some aspects of current theory that would be difficult to distinguish from a truly relativistic ether.

    It is unfortunate that the word itself carries so much historical and fringe baggage. There just does not seem to be an equivalent word – concept that bridges the gap between the math of current theory and the limitations of the lay publics understanding.

    I don't think that the concept of some kind of ether will be completely set aside, until a true Unified theory is discovered.

    In any case, I don't believe that the GP-B results eliminates the possibility that some relativistic ether exists. After all in some respects that is exactly what spacetime is. Something that interacts with matter and is detectable only by observations of the interaction between matter and matter, and matter and EM radiations. Spacetime itself is transparent. We cannot see or detect it except as it interacts with matter and EM radiation. Things we can observe and detect... And that is what the GP-B experiment has shown, that space seems to be a dynamic counter part to matter and something we can only detect, by how a material object interacts with it.

    I have to end by saying that the aether as it is most commonly defined and described historically and in many current fringe "theories", most certainly does not exist.
     
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  5. brucep Valued Senior Member

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    The experiment measured, the geodetic effect, spacetime curvature. The experiment was in the developmental stages for > 50 years. This experiment would have measured 'a geodetic effect' even if it missed the GR prediction. So maybe I should be asking is a measurement of the geodetic effect = to detecting real natural phenomena? I'm not to sure I understand what you mean by 'the relativistic aether'. Thanks for the interesting comments. Sorry I didn't 'reply with quote'. Old age issues.
     
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  7. OnlyMe Valued Senior Member

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    It measured changes in the precession of gyroscopes in orbit around the earth, over time. The explaination for those changes is that they were affected by the curvature of space. If GR is an entirely accurate description of why things are the way they appear to be, and not just a very successful predictive geometric model, then the experiment was an indirect measurement of the curvature of spacetime.

    The experiment measured, within the context of GR, curvature associated with both gravity and the Earth's spin, or frame dragging.

    I never used the phrase, "relativistic aether", I said there are relativistic ether models.... The distiction is that though both terms generally result in a bad taste in many if not most physists today, "aether" is to closely connected with the fixed space of Newtonian dynamics.

    The aether or luminiferous aether was fixed, static and did not interact with matter at all. A relativistic ether, must be dynamic and changing over time. It could even be imagined to interact weakly with matter.., in a manner that would be difficult to distinguish from the dynamic nature of space and spacetime within the context of GR.

    I am not attempting to promote "an ether" model. What I have been attempting to point out is that if one discards the deffinition associated with the aether of the 1800s, the way space and spacetime are described and modeled in GR and an ether that interacts only weakly with matter, would be difficult to distinguish one from the other. Neither one could be observed directly, but only through how matter and EM radiation is influenced by them.

    No one today can say how gravity works. All we can do is describe how matter behaves, within the context of how we experience gravity. On that account I believe GR has an upper hand over the few credible papers exploring relativistic ether I have seen. Where frame-dragging is concerned, there may be more potential for a relativistic ether, since even interacting only weakly, over time the ether or space must be considered, an active component of any inertial system. Space or the ether, either one would be "drug" along with the motion of matter and.., though only very weakly, they both must also resist that same motion.., or at least any changes in "that" motion.

    I believe that frame-dragging was the more important of the two curvatures of spacetime that the GP-B experiment confirmed. While the experiment only confirmed frame-dragging associated with the rotation or spin of a gravitational mass, it supports the second prediction that the linear motion or in the case of moons and planets the orbital motion must also drag space along weakly.

    There is no way I can imagine that we could "see" the linear equivalent of frame dragging from within an inertial system. Like the solar system or even perhaps our own galaxy. However, if a large inertial system like a galaxy, were to drag space alone with it even weakly, over time the space would have to become a dynamic component of the whole system or slowly drag the system to a stop. (If the motion of a gravitational mass drags space along, which is confirmed by the GP-B experiment, then space must offer an equal resistence to being drug along.) From the outside one cannot see the dynamics of space directly, space cannot be seen, but the motion of the space might account for at least a part of the excess galactic orbital velocities observed. Remember that large inertial systems, galaxies have had billions of years for any weak interactions with the involved space to accumulate and build up. Therefore, in any large gravitational inertia system, the curvature of space must reflect the over all dynamics of the gravitational matter within that system.

    If such were to be even partially accurate and with the confirmation of frame-dragging it must, space itself could be thought of as a dynamic componet of any gravitationally significant inertial system, the effects of which could only be observed from outside of the involved inertial system.

    While the way I present "this picture" may be awkward, I believe the intend is captured within the context and predictions of GR, terminology aside.

    So the GP-B experiment is in many ways a vital affirmation of GR, but is also establishes that space cannot be thought of as just empty, it must be thought of as having some undefined intrinsic substance, through which its interaction with matter occurs. Space must be thought of as a thing, though unless some progress is made within quantum gravity, it does not appear that it can be thought of as having observable "parts" or particle of which it is composed.

    Boy, that went way off into the "ether". (pun intended)
     
  8. brucep Valued Senior Member

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    Thanks again for your comments. I take it your opinion is the GPB measurement of the geodetic effect was indirect. Something to think about: The measurement was made in the proper frame of the GPB satellite measurement device. This measurement is an invariant spacetime event. Like measurements made in the proper frame at CERN or proper frame measurements made of the Casimir effect [force]. My example of an indirect measurement would be the remote frame measurements of the Taylor-Hulse binary neutron star orbital decay attributed to gravitational radiation.

    For some interesting stuff [physics] on frame dragging pick project F The Spinning Black Hole. On page F-13 review equation [21] L/m = angular momentum per unit mass and set L/m = 0. Begin with section 8 Plunging: the Straight-In Spiral thru section 9 Ring Riders. Queries 15 thru 25. The object falling radially will be frame dragged [figure 3]. The object has angular motion with 0 angular momentum. That's the physics of a frame dragged object. Angular motion with 0 angular momentum. After that is a really cool explanation of the Penrose Process.
    http://www.eftaylor.com/download.html#general_relativity
     
  9. Trooper Secular Sanity Valued Senior Member

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    Good stuff, thanks! There's also some interesting articles and videos to watch from this link , if you haven't already.

    http://einstein.stanford.edu/highlights/status1.html
     
  10. brucep Valued Senior Member

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    Thank you fine lady. I'm sure I didn't read Clifford Will's paper and he's a favorite of mine. As a side note we're moving back to SoCal. Duh. It's 107 today in Kansas City. Why would an old surfer and die hard Charger fan move to KC? It was great having Parker live with us for this year but beyond that it's direct proof that I'm pseudo brain dead. No offense to residents of MO. You folks are tough and very friendly.
     
  11. OnlyMe Valued Senior Member

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    I see your point re: the indirect measurement. Even though all of the measurements were in the proper frame of the sattelite, even in the GP-B experiment it is and was the affects on the gyroscopes that was measured. In that sense the curvature of space/spacetime is measured indirectly by its affect on the gyroscopes. It was predicted by GR and so supports the geometric model... Still GR is a geometric model of the interaction of objects in space and time (or spacetime) which is inherently dynamically geometric.

    I did take a look at the above reference. It is seems well written and interesting. Enough so that I have it on my list to take a look at a hard copy. I spend too much time these days with electronic information.
     
  12. Farsight

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    3,492
    How important to geometric theories is the GPB confirmation of the geodetic effect?

    Very important IMHO. Without getting sidetracked into other theories / interpretation let's just agree that GPB confirms that frame-dragging is a real phenomenum. GPB concerns the gravitomagnetic field, and in my view this ought to be waving a big red flag about the nature of the electromagnetic field. However it doesn't seem to be happening. It's been over a year since this NASA report. Here's some excerpts:

    Einstein was right again. There is a space-time vortex around Earth, and its shape precisely matches the predictions of Einstein's theory of gravity.

    "This is an epic result," adds Clifford Will of Washington University in St. Louis. An expert in Einstein's theories, Will chairs an independent panel of the National Research Council set up by NASA in 1998 to monitor and review the results of Gravity Probe B. "One day," he predicts, "this will be written up in textbooks as one of the classic experiments in the history of physics."

    But if space is twisted, the direction of the gyroscope's axis should drift over time. By noting this change in direction relative to the star, the twists of space-time could be measured.


    But there seems to be no press mention of electromagnetism in the context of vortex or twist. I find this surprising particularly when you look at images of vector fields and read On physical lines of force where Maxwell talks about vortices and mentions a screw-like mechanism. These things take time I suppose.
     
  13. Tach Banned Banned

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    Really? LOL.
     
  14. Trooper Secular Sanity Valued Senior Member

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    I don’t think it has anything directly to do with electromagnetism or with conventional magnetism, does it?

    http://www.usnews.com/science/articles/2011/05/05/gravity-probe-b-finally-pays-off

    http://en.wikipedia.org/wiki/Frame-dragging#Analysis_of_experimental_data
     
  15. brucep Valued Senior Member

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    4,098
    Frame dragging doesn't have anything to do with electromagnetism. The big error bar was related to problems with the measurement device which is documented in the GPB literature. Francis Everitt gives a brief explanation in the article you linked. The experiment was still able to detect the effect. As you know the topic of this thread was the measurement of the geodetic effect. That measurement was very accurate. I was hoping to get some response whether the geodetic measurement directly detected real natural phenomena. Spacetime curvature. I was hoping to hear a scientific opinion from folks like AN, Prom, and Pryzk. I'm guessing there's a possibility that my analysis is a 'bit silly'. And those folks might point out why 'it's scientifically silly' or not. I'm just curious about all the great experiments and theoretical models. I appreciate all the comments to this point in the thread. Thank you Trooper.
     
  16. OnlyMe Valued Senior Member

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    The GP-B experiment tracked, measured and recorded the orientation of four gyroscopes, relative to the sattelite, which istself was aligned to a guide star, all over time.

    If one interprets these results within the context of GR, the orientation of the gyroscopes represents! An indirect measurement, of the effect of the curvature of space, on those gyroscopes, over time. This is an interpretation, not a direct measurement of the curvature of spacetime. GR remains our best theoretical model applicable to the situation. The experiment thus further supports the predictions and applicability of GR.., and a geometrically curved spacetime.

    With today's technology there seems no way to directly measure the curvature of spacetime. Space itself is transparent to the methods of observation at our disposal. All we can do is observe "things" in space and interpret those observations.
     
  17. OnlyMe Valued Senior Member

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    I don't think that either electromagnetism or magnetism is directly involved, in the frame-dragging effect.

    However, the experiment did have to account for and compensate for the effects of magnetic fields both internal and external to the sattelite. The functional design of the sattelite left aspects of the experiment susceptible to being influenced by magnetic and electromagnetic fields.
     
  18. kaduseus melencolia I Registered Senior Member

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    That may be because it is, like the aether, a problem with definition.
    Initially gravity was defined differently, the motions of the heavens, and the reason a pebble remains on a beach.
    It is ony since Newton combined the two under one description that we use the term gravity as a generic term.
    Why should we treat the mechanism for a singular object the same as the mechanism for multiple objects?
    I certainly don't orbit the earth, I sit upon it, occasionally forgetting what keeps me here.

    Can I suggest you use Newtons simple description of a planar gravitational rotation, fit it into a volumetric space, and describe the problems with the mechanism using a uniform medium.
    Then switch to a non uniform medium.... the mechanism is problematic at first, but when you remember to use path of least resistance the mechanism will resolve itself.
     
  19. brucep Valued Senior Member

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    I'm pretty sure the measurements made in the proper frame of the measuring device are direct. IE: the GPB experimental device is measuring the geodetic effect on itself [the experimental measuring device]. LIGO would be directly measuring a gravitational wave as it changes the geometry [moves] of the experimental apparatus.
     
  20. OnlyMe Valued Senior Member

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    Let me start by saying that both the geodetic and frame-dragging effects exist.

    Yes those measurements are direct....., measurements of changes in the orientation of the four gyroscopes, as the sattelite orbits the earth, are direct measurements.... They remain indirect measurements of the curvature of space, which is our best explanation of why the gyroscopes are affected by the sattelites orbit in the way that they are.
     
  21. RealityCheck Banned Banned

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    Hi brucep, OnlyMe, everyone.

    Just going out, so briefly...

    OnlyMe: Can you or anyone clarify the 'status' of such a reference frame (axis aligned to star all that time) insofar as it is THE reference frame for the observations/measurements going on within the satellite/gyroscope assembly?

    Back in a couple days. Cheers!

    .
     
  22. Farsight

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    It's related. See gravitoelectromagnetism on wikipedia.

    See the Maxwell's equations section of the wiki magnetic field article, and look at curl aka rot which is short for rotor, along with Larmor precession. IMHO your amateur opinion is more correct than you currently appreciate.
     
  23. OnlyMe Valued Senior Member

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    You can find pretty much all the information available about the GP-B experiment here, http://einstein.stanford.edu/highlights/status1.html.

    Basically to insure the sattelite maintained a relatively fixed frame of reference for the test, it was designed to align itself with a guide star or fixed point in the distance relative to the earth and thus the experiment. For the data collected, to be of any use, it was important that the sattelite's orientation in space always be known and fixed. (note, that is its orientation, not its location, as it was in orbit...) The orientation of the gyroscopes was being measured relative to the sattelite. A distant fixed star was the best or easiest way to establish a relatively fixed frame of refrence for the sattelite.
     

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