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Thread: Gravity/Antigravity Research

  1. #1
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    Gravity/Antigravity Research

    I am seeking information related to an alternate view of antigravity. Perhaps someone here has run into some related information somewhere and can help with information or links. So far, my own searches just keep turning up the same concepts.

    Generally, antigravity theorists seem to believe that antigravity would have a repulsive property. In other words, whatever thing might have antigravity would accellerate away from normal matter. An alternative is that things with antigravity would repel everything else - normal gravity or antigravity.

    That view, however, seems to contradict general relativity, in which gravity is seen as a distortion or curvature of spacetime. In the area near a star, for example, matter and energy follow paths governed by the distortion of spacetime and their own momentum.

    Essentially, the concept I am researching is that gravity is an accumulated quantity. Adding more mass adds more gravity. So, if such a thing as negative mass existed, then it would subtract from gravity instead of multiplying it negatively. In that sense, it seems that instead of being directly repulsed, an antigravity "thing" might only experience a reduction in the distortion created by a larger mass.

    In Newtonian terms, F = G * (m1 + m2)/R^2. m1 and m2 are summed. When m1 is much larger than m2 (think sun vs. asteroid), if the mass of the asteroid were negative, the resulting total gravitational force is still positive, and the two masses are still attracted, but just a little less than if the asteroid had normal mass.

    The curvature of spacetime induced by the larger mass would only be partially offset by the smaller mass.

    Artistic attempts to show the effect of gravity typically show a two-dimensional plane warped by a gravity source. The complementary view would have the antigravitational field warping the plane in the opposite direction. I can mentally understand the transformation from 2-d to 3-d, but how the 3-d is warped and how it could be warped differently might work mathematically, but not visually.

    Does anyone know if and where I might find some reliable information? If you're going to tell me to look at the Einstein field equations, I'm already there.
    Depending on whom you ask, everything is relative.

  2. #2
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    In newtonian terms the masses are multiplied,

    What you have calculated is the gravitational acceleration at a certain distance from an object consisting of two seperate masses, not a gravitational force between two masses (which you can see by dimensional analysis). In any case, there's no need to use GR here, GR reduces to newtonian gravity in the low-mass low-speed limit. You neither need high mass nor high speed to get a qualitative idea about how antigravity would function. If you put a high positive mass and small negative mass (small absolute value that is ) together you're right that far away it'll look like an object with just slightly less positive mass, but the question here is of course how the positive mass and negative mass interact among themselves, not what effect their combination has on something far away.
    Last edited by caveman1917; 2013-Mar-18 at 09:19 PM.

  3. #3
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    Quote Originally Posted by caveman1917 View Post
    GR reduces to newtonian gravity in the low-mass low-speed limit.
    Thanks for the clarification. While generally the Newtonian reduction of GR is "close enough", the sensitivity of my GPS indicates that "low-mass" and "low-speed" are somewhat arbitrary. The reduction may be only 100% accurate for zero mass. Nevertheless, if the GR model allows something having a "negative mass" (and I haven't quite gotten there yet in reviewing the field equations, so I have no idea what that might be) then if GR models gravity as a bending of spacetime, then would a "negative mass" act to bend spacetime in some "opposing" direction? In the 2-d artistic representations, something like a bump in the funnel.

    Note: I've quoted some terms, because if appropriate terms already exist, I haven't found them yet, which is partially why I'm having trouble finding any information. Sort of like trying to look up something in an unabridged dictionary without any idea what the word might be or if any word even exists.
    Depending on whom you ask, everything is relative.

  4. #4
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    Well to start off with really you want to be looking at the Stress-Energy tensor as the root of gravity. Mass is only part of the picture.
    http://en.wikipedia.org/wiki/Stress%...3energy_tensor

    Your issue is going to be working with momentum fluxes that are related to a negative mass, I suspect. You will sooner or later find that there is a strong temptation to insert arbitrary moduli functions (representing the breakdown of the inertial = gravitational relationship) to get things to work.

  5. #5
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    Thanks, Shaula. I'm not opposed to analyzing the math myself. I just hoped someone else might have already done that in a way that indicated either, "you can't do that because this would ...", or "if you do that then you also have to do this, which does/means ...". If the concept had been addressed before, I hoped to at least find a discussion.
    Depending on whom you ask, everything is relative.

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