May 26, 2014
Levitation (from Latin levitas “lightness”) is the process by which an object is suspended by a physical force against gravity, in a stable position without solid physical contact. A number of different techniques have been developed to levitate matter, including the aerodynamic, magnetic, acoustic, electromagnetic, electrostatic, gas film, and optical levitation methods.
Although any electromagnetic force could be used to counteract gravity, magnetic levitation is the most common.
Diamagnetic materials are commonly used for demonstration purposes. In this case, the returning force appears from the interaction with the screening currents. For example, a superconducting sample, which can be considered either as a perfect diamagnet or an ideally hard superconductor, easily levitates in an ambient external magnetic field. The superconductor is first heated strongly, then cooled with liquid nitrogen to levitate on top of a diamagnet.
– In a very strong magnetic field, by means of diamagnetic levitation even small live animals have been levitated. Scientists have levitated frogs, grasshoppers, and mice by means of powerful electromagnets utilizing superconductors, producing diamagnetic repulsion of body water. The mice acted confused at first, but adapted to the levitation after approximately four hours, suffering no immediate ill effects.
– It is possible to levitate pyrolytic graphite by placing thin squares of it above four cube magnets with the north poles forming one diagonal and south poles forming the other diagonal.
– Pudong International Airport in Shanghai, China, sports the first commercial high-speed magnetically levitated (maglev) line in the world.
Magnetic Levitation is in development for use for transportation systems. Magnetic levitation is used to suspend trains without touching the track. This permits very high speeds, and greatly reduces the maintenance requirements for tracks and vehicles, as little wear then occurs. This also means there is no friction, so the only force acting against it is air resistance. Due to the lack of friction on guide rails, they are potentially faster, quieter and smoother than wheeled mass transit systems.
Other levitation methods:
A number of different techniques, that don’t involve magnetism, have been developed and are commonly used to produce the stable levitation of matter:
– Electrostatic Levitation, whereby levitation an electric field is used to counteract gravitational force.
– Aerodynamic Levitation is achieved by floating the object on a stream of gas, either produced by the object or acting on the object. For example, a ping pong ball can be levitated with the stream of air from a vacuum cleaner set on ‘blow’.
With enough thrust very large objects can be levitated using this method. Hovercrafts however do not use powerful downthrusts to achieve stable levitation but instead rely on producing a region of high pressure underneath them.
– Acoustic levitation uses sound waves to provide a levitating force.
– Gas Film: This technique enables the levitation of an object against gravitational force by floating on a thin gas film formed by gas flow through a porous membrane. A common example of this is air hockey, where the puck is lifted by a thin layer of air.
– Optical Levitation is a technique in which a material is levitated against the downward force of gravity by an upward force stemming from photon momentum transfer.
– Casimir Force: Scientists have discovered a way of levitating ultra small objects by manipulating the so-called Casimir force, which normally causes objects to stick together due to forces predicted by quantum field theory. This is, however, only possible for micro-objects.
– Buoyant Levitation: Gases at high pressure can have a density exceeding that of some solids. Thus, they can be used to levitate solid objects through buoyancy. Noble gases are preferred for their non-reactivity. Xenon is the densest non-radioactive noble gas, at 5.894g/L. Xenon has been used to levitate polyethylene, at a pressure of 154atm.
– Gravity Shields: In 1948 successful businessman Roger Babson formed the Gravity Research Foundation to study ways to reduce the effects of gravity. Their efforts were initially seen as somewhat “crankish”, but they held occasional conferences that drew such people as Clarence Birdseye of frozen-food fame and Igor Sikorsky, inventor of the helicopter.
– US Gravity Control Propulsion Research (1955â€“1974): Military support for anti-gravity projects was terminated by the Mansfield Amendment of 1973, which restricted Department of Defense spending to only the areas of scientific research with explicit military applications. The Mansfield Amendment was passed specifically to end long-running projects that had little to show for their efforts.
Under the general relativity, gravity is the result of following spatial geometry (change in the normal shape of space) caused by local mass-energy. This theory holds that it is the altered shape of space, deformed by massive objects, that causes ‘gravity’, which is actually a property of deformed space rather than being a true force. Although the equations cannot produce a “negative geometry” normally, it is possible to do so using a “negative mass”. The same equations do not, of themselves, rule out the existence of negative mass.
Both general relativity and Newtonian gravity appear to predict that negative mass would produce a repulsive gravitational field. In particular, Sir Hermann Bondi proposed in 1957 that negative gravitational mass, combined with negative inertial mass, would comply with the strong equivalence principle of general relativity theory and the Newtonian laws of conservation of linear momentum and energy. Bondi’s proof yielded singularity free solutions for the relativity equations. In July 1988, Robert L. Forward presented a paper at the AIAA/ASME/SAE/ASEE 24th Joint Propulsion Conference that proposed a Bondi negative gravitational mass propulsion system.
Every point mass attracts every other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses.
– Bondi Negative Gravitational Mass Propulsion System: a negative mass will fall toward (and not away from) “normal” matter, since although the gravitational force is repulsive, the negative mass (according to Newton’s law, F=ma) responds by accelerating in the opposite of the direction of the force. Normal mass, on the other hand, will fall away from the negative matter. He noted that two identical masses, one positive and one negative, placed near each other will therefore self-accelerate in the direction of the line between them, with the negative mass chasing after the positive mass. Notice that because the negative mass acquires negative kinetic energy, the total energy of the accelerating masses remains at zero. Forward pointed out that the self-acceleration effect is due to the negative inertial mass, and could be seen induced without the gravitational forces between the particles.
The Standard Model of particle physics, which describes all presently known forms of matter, does not include negative mass. Although cosmological dark matter may consist of particles outside the Standard Model whose nature is unknown, their mass is ostensibly known â€“ since they were postulated from their gravitational effects on surrounding objects, which implies their mass is positive. (The proposed cosmological dark energy, on the other hand, is more complicated, since according to general relativity the effects of both its energy density and its negative pressure contribute to its gravitational effect.)
– Fifth force: Under general relativity, any form of energy couples with spacetime to create the geometries that cause gravity. A longstanding question was whether or not these same equations applied to antimatter. The issue was considered solved in 1960 with the development of CPT symmetry, which demonstrated that antimatter follows the same laws of physics as “normal” matter, and therefore has positive energy content and also causes (and reacts to) gravity like normal matter (see gravitational interaction of antimatter).
For much of the last quarter of the 20th century, the physics community was involved in attempts to produce a unified field theory, a single physical theory that explains the four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. Scientists have made progress in unifying the three quantum forces, but gravity has remained “the problem” in every attempt. This has not stopped any number of such attempts from being made, however.
Generally these attempts tried to “quantize gravity” by positing a particle, the graviton, that carried gravity in the same way that photons (light) carry electromagnetism. Simple attempts along this direction all failed, however, leading to more complex examples that attempted to account for these problems. Two of these, supersymmetry and the relativity related supergravity, both required the existence of an extremely weak “fifth force” carried by a graviphoton, which coupled together several “loose ends” in quantum field theory, in an organized manner. As a side effect, both theories also all but required that antimatter be affected by this fifth force in a way similar to anti-gravity, dictating repulsion away from mass. Several experiments were carried out in the 1990s to measure this effect, but none yielded positive results.
– General-Relativistic “Warp Drives”: There are solutions of the field equations of general relativity which describe “warp drives” (such as the Alcubierre metric) and stable, traversable wormholes. This by itself is not significant, since any spacetime geometry is a solution of the field equations for some configuration of the stressâ€“energy tensor field (see exact solutions in general relativity). General relativity does not constrain the geometry of spacetime unless outside constraints are placed on the stressâ€“energy tensor. Warp-drive and traversable-wormhole geometries are well-behaved in most areas, but require regions of exotic matter; thus they are excluded as solutions if the stressâ€“energy tensor is limited to known forms of matter. Dark matter and dark energy are not understood enough at this present time to make general statements regarding their applicability to a warp-drive.
– Breakthrough Propulsion Physics Program: During the close of the twentieth century, NASA provided funding for the Breakthrough Propulsion Physics Program (BPP) from 1996 through 2002. This program studied a number of “far out” designs for space propulsion that were not receiving funding through normal university or commercial channels. Anti-gravity-like concepts were investigated under the name “diametric drive”. The work of the BPP program continues in the independent, non-NASA affiliated Tau Zero Foundation.
– Empirical Claims and Commercial Efforts: There have been a number of attempts to build anti-gravity devices, and a small number of reports of anti-gravity-like effects in the scientific literature. None of the examples that follow are accepted as reproducible examples of anti-gravity.
– Gyroscopic devices: A “kinemassic field” generator from U.S. Patent 3,626,605: Method and apparatus for generating a secondary gravitational force field.
Gyroscopes produce a force when twisted that operates “out of plane” and can appear to lift themselves against gravity. Although this force is well understood to be illusory, even under Newtonian models, it has nevertheless generated numerous claims of anti-gravity devices and any number of patented devices. None of these devices have ever been demonstrated to work under controlled conditions, and have often become the subject of conspiracy theories as a result. A famous example is that of Professor Eric Laithwaite of Imperial College, London, in the 1974 address to the Royal Institution.
– Another “rotating device” example in shown a series of patents granted to Henry Wallace between 1968 and 1974. His devices consist of rapidly spinning disks of brass, a material made up largely of elements with a total half-integer nuclear spin. He claimed that by rapidly rotating a disk of such material, the nuclear spin became aligned, and as a result created a “gravitomagnetic” field in a fashion similar to the magnetic field created by the Barnett effect. No independent testing or public demonstration of these devices are known.
In 1989, it was reported that a weight decreases along the axis of a right spinning gyroscope. A test of this claim a year later yielded null results. A recommendation was made to conduct further tests at a 1999 AIP conference. Thomas Townsend Brown’s gravitator.
– Biefeld-Brown effect: Electrogravitics and United States Gravity Control Propulsion Research; Brown’s Gravitator: In 1921, while still in high school, Thomas Townsend Brown found a high-voltage Coolidge tube seemed to change mass depending on its orientation on a balance scale. Through the ’20s Brown developed this into devices that combined high voltages with materials with high dielectric constants (essentially a large capacitors) that he called a “gravitator”. Brown made the claim to observers and in the media that his experiments were showing anti-gravity effects. Brown would continue his work and produced a series of high-voltage devices in the following years in attempts to sell his ideas to aircraft companies and the military. He coin the names Biefeldâ€“Brown effect and electrogravitics in conjunction with his devices. Brown tested his asymmetrical capacitor devices in a vacuum supposedly showing it was not a more down to earth electrohydrodynamic effect generated by high voltage ion flow in air.
Electrogravitics is a popular topic in ufology, anti-gravity, free energy, government conspiracy theorists and related websites, books and publications with claims the technology became highly classified in the early 1960s and that it is used to power UFOs and the B-2 bomber. There is also research and videos on the internet purported to show lifter-style capacitor devices working in a vacuum, therefor not receiving propulsion from ion drift or ion wind being generated in air.
Follow-up studies on Brown’s work and other claims have been conducted by R. L. Talley in a 1990 US Air Force study, NASA scientist Jonathan Campbell in a 2003 experiment, and Martin Tajmar in a 2004 paper. They have found that no thrust could be observed in a vacuum and that Brown’s and other ion lifter devices produce thrust along their axis regardless of the direction of gravity consistent with electrohydrodynamic effects.
– Gravitoelectric Coupling:
In 1992, the Russian researcher Eugene Podkletnov claimed to have discovered, whilst experimenting with superconductors, that a fast rotating superconductor reduces the gravitational effect. Many studies have attempted to reproduce Podkletnov’s experiment, always to negative results.
Ning Li and Douglas Torr, of the University of Alabama in Huntsville proposed how a time dependent magnetic field could cause the spins of the lattice ions in a superconductor to generate detectable gravitomagnetic and gravitoelectric fields in a series of papers published between 1991 and 1993. In 1999, Li and her team appeared in Popular Mechanics, claiming to have constructed a working prototype to generate what she described as “AC Gravity.” No further evidence of this prototype has been offered.
Douglas Torr and Timir Datta were involved in the development of a “gravity generator” at the University of South Carolina. According to a leaked document from the Office of Technology Transfer at the University of South Carolina and confirmed to Wired reporter Charles Platt in 1998, the device would create a “force beam” in any desired direction and that the university planned to patent and license this device. No further information about this university research project or the “Gravity Generator” device was ever made public.