Anti-gravity
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Anti-gravity is a hypothetical means of countering or otherwise modifying the effects of gravity, typically in the context of spacecraft propulsion. Such systems are limited to the realm of science fiction given the current understanding of the way gravity works, but this has not stopped legions of hopefuls from making various spinning disks and magnets in hopes of perfecting such a device.
The United States government and aerospace contractors publicly announced ambitious Manhattan project-style goals to crack the anti-gravity problem during the mid-1950's while the atomic airplane was on the drawing board, but by the end of 1957 no more information was flowing into the newspapers and magazines. Either their work never produced anything, or the projects were taken into the world of top secret.
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Anti-gravity in the context of mainstream physics
- Newton's Law of Gravitation considered gravity to be a force between two objects, causing attraction in proportion to the objects' mass. Under this interpretation, an object with negative mass would be repelled by ordinary matter, and could be used to produce an anti-gravity effect. Alternatively, depending on the mechanism assumed to underlie the gravitational force, it may seem reasonable to postulate a material that shields against gravity or otherwise interferes with the force. An example of such a material, cavorite, is a major deus ex machina of H. G. Wells' famous book, The First Men in the Moon, though it should be noted that Cavorite isn't consistent with even a Newtonian view of the universe (it causes violations of conservation laws). Neither negative-mass exotic matter nor a gravity-screening material have been observed experimentally. While the potential existence of exotic matter is still debated, general relativity presents persuasive arguments against the existence of screening materials.
- Einstein's theory of general relativity, published in 1915, supplanted Newton's model of gravity with an entirely different mechanism - one based entirely on the geometry of the universe. Gravity was no longer a force at all, but simply the consequence of the local slope of the universe in a direction the human eye cannot see: time. You stick to the floor not because gravity is pulling you down, but because that is the shortest distance between today and tomorrow. Under this model, gravity in a universe containing only matter with positive mass is purely attractive. No arrangement of ordinary matter can produce an anti-gravity effect. Spacetime geometries corresponding to true anti-gravity in general relativity require negative mass.
Some models of anti-gravity claim to derive from general relativity.
- The model of gravity proposed by the theory of general relativity breaks down under extreme conditions (too far inside a black hole, and in the very early life of the universe under the big bang model). In particular, most physicists believe that at extremely high energies, gravity and the other fundamental forces unify, which would allow gravity to be manipulated in ways that are not readily apparent now. Candidate models for this regime are theories of everything, which attempt to model all four forces (example: string theory), and theories of quantum gravity, which attempt to produce a model of gravity that is consistent with quantum mechanics, though not necessarily unified with the other forces.
Some models of anti-gravity claim to be based on quantum gravity models, though the connection of these to mainstream quantum gravity models is often tenuous.
Conventional effects that look like anti-gravity
- Magnetic levitation suspends an object against gravity by use of electromagnetic effects. While visually impressive, this is not an anti-gravity effect.
Critics of various alleged anti-gravity devices often suggest that unusual effects observed around them are due to electromagnetism.
- A tidal force causes objects to move along diverging paths near a massive body (such as a planet or star), producing effects that seem like repulsion or disruptive forces when observed locally. This is not anti-gravity. In Newtonian mechanics, the tidal force is the effect of the larger object's gravitational force being different at the differing locations of the diverging bodies. In Einsteinian gravity, the tidal force is the effect of the diverging bodies following different paths in the negatively curved spacetime around the larger body.
- Large amounts of normal matter can be used to produce a gravitational field that compensates for the effects of another gravitational field, though the entire assembly will still be attracted to the source of the larger field. Physicist Robert L. Forward proposed using lumps of degenerate matter to locally compensate for the tidal forces near a neutron star.
- The accelerating expansion of the universe due to dark energy is an effect that causes a large-scale repulsive force. However, this is not gravitational in nature, and so is not anti-gravity.
Anti-gravity in the context of non-mainstream physics
- In the 1990s, a Russian emigre scientist Eugene Podkletnov reported gravity shielding with spinning superconductors. Podkletnov claims he saw tobacco smoke rise over the spinning superconductor, so he measured the gravitational acceleration above the device and made the discovery. Podkletnov now claims to have created a force beam that is 200 times stronger than his first experiments.
NASA, Boeing, and BAe have all funded Podkletnov reproduction experiments, with little to no results.
- Another American scientist, Ning Li, independently predicted a gravity shielding effect with superconductors at nearly the same time as Podkletnov's announcements.
- In the 1970s, an American scientist proposed use superfluid helium in a toroidal vessel to create gravity control.
Related topics
Non-mainstream antigravity external links
As the effects described by the following links haven't been unambiguously replicated or described in peer-reviewed journals by people other than the effects' proponents, they are often claimed to be pseudoscience. Proponents of these anti-gravity models in turn often claim that they are dismissed out of hand without attempts at replication by the mainstream scientific community.
- http://www.americanantigravity.com - A non-profit organization containing a large database of information about alleged anti-gravity effects.
- http://www.space-mixing-theory.com/abstract2.htm - A web site describing apparent weight loss in charged capacitors.
- http://groups.yahoo.com/group/electrogravityresearch - Newsgroup discussions of an alleged anti-gravity device sold on the public market.
- http://jnaudin.free.fr/ - JLN Labs web site dedicated to the search of Free-Energy solutions and new generation of space-propulsion systems.
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