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When will we have anti gravity?

  1. Jul 22, 2006 #1
    It would probably be the biggest discovery known to mankind if we found out how to counteract the "force" of gravity. It kind of seems impossible; given that GR is correct, gravity is geometric, and is a result of curved spacetime.

    Perhaps if we found out about the "dark energy" that's expanding the universe and acting against gravity, will we be able to create antigravity devices?

    Imagine the manipulation of gravity!! No more oil, no more pollution, etc. Space travel far and beyond, maybe even time travel.
     
  2. jcsd
  3. Jul 22, 2006 #2

    Jorrie

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    Don't you think it will take energy to "manipulate gravity"?
     
  4. Jul 22, 2006 #3
    Well I doubt we will be able to consider it till we have a real TOE that resolves the assumptions like the one you've made here.
    Regardless of what high level physics put out in books or TV shows where they are trying to combine GR and QM, the key in all that is that they are TRYING. They have not done so, and as GR and QM stand now and always have they are not compatible and contradict each other in their basic understanding of reality. That means one or both must be wrong until something new is added or changed to give a complete description of physics. IMO only one of the two theories can survive not both, maybe nether one will.

    Once we do have a GUT and TOE, I suspect we have a good chance of learning that gravity cannot be counteracted or manipulated.
     
  5. Jul 22, 2006 #4
    Clearly both theories are correct in appropriate limits, as they have both individually made quantitative (and surprising) predictions that have since been confirmed experimentally. Both theories must survive in the appropriate limits of any "unified" theory.
     
  6. Jul 23, 2006 #5
    I disagree, a theory only good "in appropriate limits" is an incomplete theory. As both, GR & QM show the explanation offered by Newtonian Classical theory to be incomplete, it is never the less still quite useful.
    Einstein worked to complete GR by building a GUT to explain Electricity, Magnetism, and Gravity in one unified theory. (IMO doing so would also explain weak and strong as well for a full TOE, even though Einstein never worked on that).

    Niels Bohr claimed QM is complete in that nature will never let us see beyond the HUP, to find an unknown hidden variable. To which Einstein never agreed, and to this day GR vs. QM and the Standard Model are incompatible.
    Although I agree both are quite useful, neither have been shown to be complete, both are still at odds with each other.
    If you have trouble accepting that, pick from a few of the many credible Physicists you can find on a Brain Greene DVD to confirm it.
    The same Elegant Universe DVD will also talk about the DREAM of STRINGS where it requires a simple combining of GR & QM, but that “simple” result of Strings does not seem to come with a simple explanation of how or why they are compatible at all. We are to just trust and wait for the theory to produce a TOE.
    For me I do not buy that dream, and expect the string folks to come up with a proof before I will.

    IMO a simple understanding of the difference between GR demands of gravity based on four-dimensional curves and warps vs. QM expectation of particle exchanges, clearly shows they cannot both survive.
     
  7. Jul 23, 2006 #6
    EM just as much about as geometry is as gravity.


    Pete
     
    Last edited: Jul 23, 2006
  8. Jul 27, 2006 #7

    Office_Shredder

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    How to counteract gravity?

    Have you tried a pulley?



    Imagine you have some sort of anti-gravity shield. Take a big wheel, and put the shield under half of it. The wheel starts to spin. Free energy! Yay
     
  9. Jul 27, 2006 #8
    Actually anti-gravity is observed in nature. It is now apparant that the universe is expanding at an accelerated rate. This can be accomplished by introducing a non-zero cosmological constant into Einstein's equations of gravity. This non-zero cosmological constant acts in nature as anti-gravity. Einstein introduced this constant so as to allow for what he assumed as a static universe. Such a universe was held apart by anti-gravitational forces. Objects in GR such as a vacuum domain wall act as objects which forces/gravitationally accelerates particles away from the wall - i.e. antigravity.

    Pete
     
    Last edited: Jul 27, 2006
  10. Jul 27, 2006 #9

    Aether

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    How about that column of air above the anti-gravity shield. If it no longer has weight, then the atmospheric pressure due to the gravity acting on the rest of the atmosphere will cause the entire atmosphere to be purged into space. :surprised

    So, if your invention ever does turn this big wheel for free, then it will also immediately wipe out all life (aerobic life anyway) on earth...seems like a serious glitch. :bugeye:
     
    Last edited: Jul 27, 2006
  11. Jul 27, 2006 #10
    Not really, the air above say a “shield” with a 5 ft radius is not held in place by gravity acting directly on it mass. And the weight of the air close to the shield would have an insignificant effect in the local air pressure. Whoever the loss of weight for the air just a few feet above would be minor and even smaller the high you go in the air column as most of the effect of gravity on the individual parts would be small as most of the earth is still visible as a source of gravity for miles around this tiny little shield.

    Also I except conservation laws to hold, and we shouldn’t expect the gain of “Free Energy” created by the shield local would result in even more energy being created in the form of gases jetting out away from earth.

    Not included with the idea of a shield is an accounting for just where or how the total energy balance will be maintained. It should explain what reaction is expected where to balance the apparent gain in local energy in the turning “anti-gravity” wheel. Such a shield is not going to provide a free lunch by moving the wheel and creating some weird local air currents. The real glitch is the idea holds out no option to explain where the energy would be lower as a result of the local gain.
     
  12. Jul 27, 2006 #11

    selfAdjoint

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    I don't believe this analysis. Consider gravitational potential energy. The region immediately outside the circle is at zero gravitational potential relative to itself. Immediately inside the circle the potential would be "infinite"; at least a very huge number, relative to the earth's surface. The physics at this discontituity cannot just be handwaved away. I remember an old discussion of this issue in Astounding Science Fiction magazine (as it still was at that date in the fifties of tha last century). They concluded that the physics discontinuity was a deal buster.
     
  13. Jul 27, 2006 #12

    Aether

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    It's not? :bugeye:
    My point is to illustrate why we wouldn't be well served by having such things around even if it were possible. Some people seem to think that it would be great if we had access to such things.
     
  14. Jul 27, 2006 #13

    pervect

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    There would be a lot of unpleasant consequences to having some "lump form" of exotic matter (i.e. matter with a negative mass) as well.

    The key point is that if you push on it, the exotic matter will move towards the push, because it has a negative inertial mass.

    This leads to a rather large variety of unpleasant behaviors.
     
  15. Jul 27, 2006 #14

    DaveC426913

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    You assume way too many absolutes. Absolute range (as opposed to diminishing), absolute speed (as if it would pour out of the Earth all at once) and all sorts of others.

    That's like saying 'if we Earthlings ever invented the magnet, we would immediately be crushed by the Moon!'
     
    Last edited: Jul 27, 2006
  16. Jul 28, 2006 #15

    Aether

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    I did assume that the gravitational mass of the earth was concentrated at a point which is a standard assumption for modeling orbits, but it doesn't work out here as RandallB said. I didn't assume absolute speed: the air would pour out at the speed of sound; that and the radius of the evacuating cylinder would determine the rate at which the air poured out...then the seas would vaporize, I forgot to mention that.
     
    Last edited: Jul 28, 2006
  17. Jul 28, 2006 #16
    Maybe when we have anti-mass?

    Or something that curves spacetime in the other direction?
     
    Last edited: Jul 28, 2006
  18. Jul 28, 2006 #17
    Of course not - how much does one cubic foot of air just above the "shield" weigh do you think? How is that tiny weight going to compare with the 14lb/sq in pushing from all sides going to compare?
     
  19. Jul 28, 2006 #18
    I have no clue what you are talking about.
    SHREDDER was talking about a “Shield” not some negative mass or some "infinite" potential “inside a circle”. (I understand gravitational potential inside a sphere but not inside a flat circle.)

    If you are trying to construct some mathematical model for such an impossible Shield, worrying about the interior of the shield is like claiming to know what a singularity looks like.
    Showing that such a shield will not blow off our atmosphere is easy.
    But building a rational explanation of how the law of energy conservation could be maintained is so unlikely that I suspect someone, much better at math than I, could show the law would have to be violated for such a shield to exist.
     
  20. Jul 28, 2006 #19

    DaveC426913

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    Again, said as if a fridge magnet would suck the Moon down from the sky.

    Why do you assume the effect would extend to the edge of the atmosphere instead of falling off logarythmically and having a barely useful range?

    Why would it not be dependent on the power of the device? Say, 10,000 watts gets you antigravity in a one cubic inch volume?

    Now you've got a one cubic inch volume of air that weighs nothing. Or almost nothing (nobody said the effect was a simple on/off).

    You could still scale it up, but - like almost every other engineering effort we're familiar with, it would be difficult (though not impossible) to scale it up to commmercially-viable levels.

    And nobody said it would be energy-efficient. An anti-gravity engine might replace the jets in a 747, but might be as heavy and use as much fuel.
     
  21. Jul 28, 2006 #20

    Aether

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    For simplicity, let's consider just one nitrogen molecule at mean sea level (MSL) and standard temperature and pressure (STP) instead of one cubic foot of air, and then see if we can predict what would happen to it if gravity were not acting directly on its mass, ok? My initial guess is that it would be out in space within a matter of minutes.
     
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