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I want to know if there is any anti-gravity material. I am thinking of making flying vehicles which are made up of anti-gravity material so that they will not experience any gravity on them and can easily take off and be more fuel efficient. Is there any such thing? Or any workaround?

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@downvoters and other commentators: I voted up made it from -2 to -1 since I have no answer for this simple question. Please be gentle with questioners. I would also appreciate if you, knowledgeable person, provide us a simple but reasonable logical answer to the question. You may explain more talking about anti-material too. Everybody can google so if you have something to share please do it otherwise just pass it. –  Developer Nov 2 '11 at 11:06
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I am also tempted to downvote because physics.stackexchange requires at least a tiny bit of own research effort to be successful. The person asking the question did not even use wikipedia to look up the term. The article on anti-gravity is well written there and explains why a simple anti-gravity material does not exist and possible directions for future work. I am also in favor of gentle treatment of questioners but a simple google or wikipedia search is not too much to ask for. –  Alexander Nov 2 '11 at 12:02
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See meta: meta.physics.stackexchange.com/q/952 –  David Z Nov 2 '11 at 21:35
    
isn't helium anti-gravity material? it does make balloons define gravity, just because it's gas don't mean it's not material? –  Val Jan 4 '13 at 14:00
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Hm.. this makes me remember a video of Feynman where some audience member asked him if there was any way to make an anti-gravity machine, to which he replied: your butt's one such machine. –  nervxxx Apr 8 '13 at 0:59

6 Answers 6

up vote 9 down vote accepted

When you say "anti-gravity material", the closest thing I can think of is the hypothetical concept of negative mass:

In theoretical physics, negative mass is a hypothetical concept of matter whose mass is of opposite sign to the mass of the normal matter. Such matter would violate one or more energy conditions and show some strange properties such as being repelled rather than attracted by gravity. It is used in certain speculative theories, such as on the construction of wormholes. The closest known real representative of such exotic matter is a region of pseudo-negative pressure density produced by the Casimir effect.

But it gets more complicated because there are actually three different kinds of mass: gravitational mass, passive grativational mass, and inertial mass:

Thus objects with negative passive gravitational mass, but with positive inertial mass, would be expected to be repelled by positive active masses, and attracted to negative active masses. However, any difference between inertial and gravitational mass would violate the equivalence principle of general relativity. For an object where both the inertial and gravitational masses were negative and equal, we could cancel out mi and mp from the equation, and conclude that its acceleration a in the gravitational field from a body with positive active gravitational mass (say, the planet Earth) would be no different from the acceleration of an object with positive passive gravitational and inertial mass (so a small negative mass object would fall towards the Earth at the same rate as any other object).

In any case, there does not exist any such thing, to the extent of human knowledge.

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Which is precisely why this is a good question! Why is gravity attractive?? Granted this is more philosophical than physics, it is still on the minds of us theorists. –  Chris Gerig Nov 28 '11 at 20:28
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@ChrisGerig: I have often heard it stated that the attractiveness of gravity is a feature of all spin 2 gauge theories. –  Jerry Schirmer Dec 6 '12 at 14:54
    
@JerrySchirmer Why is this so? –  namehere Dec 6 '12 at 16:09
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@namehere: I've never seen it adequately proven. But I have heard that statement many times. –  Jerry Schirmer Dec 6 '12 at 17:18
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@JerrySchirmer The proof is in Zee's QFT book in one of the early chapters. It's due to a simple pattern: spin-0 exchange -> universal attraction, spin-1 exhange -> attraction&repulsion, spin-2 exchange -> universal attraction, spin-3 exchange -> attraction&repulsion etc. Then there is a theorem that rules out interacting spin > 2 particles so all that's left is spin-0 (Higgs/pions), spin-1 (gauge bosons) and a single spin-2 (graviton). –  Michael Brown Apr 8 '13 at 2:26

In the spirit of conspiracies and dubious theories, take a look at the so called Biefeld Brown effect.Some have claimed that Penney's 1965 paper as a possible source of rationalizing their beliefs. I don't know enough to offer an opinion either way. However, Mythbusters et al have obtained negative results in all their experiments.Take it for what its worth.

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Forget anti-gravity material. As far as we know, there is none--gravity is always an attractive force. But there is a workaround: Use something with the appropriate properties, i.e. something that does have repelling force. Electromagnetism! All you need to do is separate enough charge, say a few grams of electrons, place half of them at the airport and attach the other half to your flying machine. Off they go with a mighty force that can lift Mount-Everest sized objects to the moon. Simple as that. (Calculation of the force between two 1g clouds of electrons left as an exercise--it's immense!).

Of course, the hard part is getting at a gram of electrons (without any positive charge nearby).

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And hey! We have mag-lev trains already! –  Jerry Schirmer Dec 6 '12 at 14:56

A from a theoretical physics point of view not completely off the mark approach to anti-gravity effects comes from certain versions of supergravity described in wikipedia, which is a unified supersymmetric point-particle quantum field theory.

Some particular versions of this theory not only contain the "usual" atractive graviton, a spin-2 particle, but in addition a so-called graviphoton is predicted (1). This graviphoton is a spin-1 vector field, interacts with mattar at the normal gravitational strength, and behaves generally like a massive photon. The fun thing about it is that it can give rise to attractive and repulsive forces. The repulsive forces feature can in principle give rise to anti-gravity effects, however the real-world / everyday usefulness of this has not yet been tested ... ;-)

For more see this blog article on Uduality (2).

References:

(1) A model for a light graviphoton, R. Barbiery and S. Cecotti, Zeitschrift für Physik C Particles and Fields, 33(2), 1986, 255-261

(2) Antigravity from Supergravity, Physics blog post on: U.Duality thoughts on the new mathematics and physics, posted 24. November 2012

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I dont know why people have to downvote (again without saying what is technically or physically wrong!) my answer here; supergravity is an accepted mainstream high energy physics theory. Must be non physics reasons then ... -> Not cool, this takes away the fun of posting anything here on this site :-/ –  Dilaton Apr 7 '13 at 19:02
    
+1 but The link seems to be broken. Could you fix it? –  Dimensio1n0 Jun 22 '13 at 14:59
    
@dimension10 I can fix it in about 24 hours, I am currently traveling and typing on my iphone ... –  Dilaton Jun 22 '13 at 22:04
    
@dimension10 hm, from my laptop when I use firefox for example, the links seem to work. I can however add some information to retreave the posts by googling in case it does not work for some reason. –  Dilaton Jun 24 '13 at 13:00
    
I tried again and now it works. For some reason, there is some serious problem with my internet these days. It singles out certain sites (e.g. the entire of Physics S.E., or arXiV, or certain blogs some times) for a period of time and simply gives random error messages. Maybe I should wait for a longer time before commenting... –  Dimensio1n0 Jun 24 '13 at 14:00

Anti-gravity is impossible, as it would let you build a perpetual motion system, as follows.

Assume we have a system in which we can capture the kinetic energy of a falling mass. For example, a ball that falls onto a scooped wheel to drive it. Take the ball and move a sheet of anti-grav material under it. As the ball now no longer feels the earth's gravity, we can push it up above the wheel without using any energy. Now remove the anti-grav sheet. The ball will fall onto the wheel and thus generate energy.

This violates the law of conservation of energy, i.e. the first law of thermodynamics. Hence it is impossible, and hence anti-gavity cannot exist.

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It doesn't have to violate conservation of energy if moving the sheet needs appropriate amounts of energy. You simply assume it doesn't. –  Jens Apr 8 '13 at 7:50
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This is wrong for three reasons. First, you need energy to move the object because it still has inertial mass. Second, the sheet will move. Third, the sheet (planar) will not homogenously shield the gravitational field of the earth (sphere). –  WIMP Apr 8 '13 at 8:18

What does General Relativity have to say about this issue?

Instead of going into more recent developments, which others, such as Dilaton already have, I will discuss the general relativistic perspective on this. So, start with the Raychaudhuri Equation:

$$\frac{\mbox{d}\theta}{\mbox{d}\tau}=-\left(\theta^2+\sigma^2\right)-R_{\mu\nu}v^{\mu}v^\nu$$

With $\theta^2$ and $\sigma^2$ are appropriately defined as $\theta^2=\left(\frac{\theta_\mu^\mu}{3}\right)^2$ and $\sigma^2=\sigma_{\mu\nu}\sigma^{\mu\nu}$ and also, under the assumption that the worldline of the centre of energy is completely time-like. Just for the time being, forget about $\sigma^2$.i.e. say that the object is not under any shearat all. $$\frac{\mbox{d}\theta}{\mbox{d}\tau}=-\theta^2-R_{\mu\nu}v^\mu v^{\nu}$$

Now, for there to be any anti-gravitational effect, $R_{\mu\nu}v^\mu v^{\nu}$ must be positive. Whether or not the worldlines go forward in time, or backwards, $v^\mu v^\nu$ must be negative since it is completely time-like, and thus, $R_{\mu\nu}$ must be negative. Now apply the Einstein Field Equation: $$G_{\mu\nu}=\kappa T_{\mu\nu}$$ $$R_{\mu\nu}=\kappa\left({T_{\mu\nu}-\frac{T}{2}g_{\mu\nu}}\right)$$

Thus, the anti-gravity condition imposes the following constraint: $$T_{\mu\nu}<\frac{T}{2}g_{\mu\nu}$$

Taking the trace of the inequation with respect to the Minkowski metric tensor (for fun, or maybe not really), letting $g=g_\mu^\mu$: $$T<\frac{T}{2}g$$ $$g>2$$ Wow, like we didn't know that before from the Einstein Field Equation before!

Conclusion: General Relativity does not disallow antigravity. Only a negative time-time component of the SEM tensor is necessary. : )

What does Newtonian Gravity have to say about this issue?

Let's go a step simpler and just handle Newtonian Gravity now. Well, you know this. Its really simple.

$$\|\vec F\|<0$$ $$G\frac{m_1m_2}{r^2}<0$$ $$\frac{m_1m_2}{r^2}<0$$

SPATIAL distances are always real numbers so the denominator must be non-negative. $$m_1m_2<0$$

Solutions:

  1. Tachyons...

PROBLEM: TACHYON CONDENSATION (SEN CONJECTURE)

  1. One negative mass, one positive mass...

NO PROBLEM!

enter image description here

Due to lack of spacetime, I couldn't write that Newton was actually telling Einstein that even Kindergarden kids could learn his theory of gravity but not the latter's! And that Einstein was mocking Newton.

Image Courtesty Wikipedia :).!

For your specific case, however, don't bother buying so much negative stress-energy-momentum tensor, instead just use two magnets (like poles repell) or really light objects.

Edit: Oops! I mean "lack of space"!

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protected by Qmechanic Apr 7 '13 at 15:27

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