In 1667, Newton mathematically deduced the nature of gravity, demonstrating that the same force that pulls an apple down to earth also keeps the moon in its orbit and accounts for the revolutions of the planets.
But today, we are still thwarted in attempts to measure it with any great precision.
In lab experiments carried out since the 1930s, gravity has consistently defied efforts to be measured to more than a few decimal places.
According to Einstein, gravity is not some kind of "force field", like magnetism, which can - in principle at least - be screened out.
Newton's model was replaced by the more general and complete description encoded in general relativity.
Instead, General Relativity (see "Relativity" topic page) views gravity as a distortion in the very fabric of space and time, that permeates the whole cosmos. As such, any claim to have shielded objects from gravity is to challenge Einstein himself.
In the first mathematically accurate description of gravity, Newton's law of universal gravitation, gravity was an external force transmitted by unknown means.
According to General Relativity, anti-gravity is deemed to be highly unlikely or even, impossible.
According to the major directions of physical research, it is considered highly unlikely that anti-gravity is possible.
Under Newtonian gravitation, where gravity is a force being transmitted from point to point, this approach made sense; the gravitational field would be blocked by an appropriate shield in the same way a magnetic field could be blocked by diamagnetic substances.There are strong reasons to believe that no such substance can exist. Consider the results of placing such a substance under one-half of a wheel on a shaft. The side of the wheel under the substance would have no weight, while the other side would. This would cause the wheel to continually "fall" toward the side under the plate. This motion could be harnessed to produce power for free, a clear violation of the first law of thermodynamics. More generally, it follows from Gauss's law that static inverse-square fields (such as Earth's gravitational field) cannot be blocked (magnetism is static, but is inverse-cube).
It is claimed the US Air Force also ran a study effort throughout the 1950s and into the 1960s.Former Lieutenant Colonel Ansel Talbert wrote two series of newspaper articles claiming that most of the major aviation firms had started gravity control propulsion research in the 1950s. However there is little outside confirmation of these stories, and they take place in the midst of the policy by press release era, it is not clear how much weight these stories should be given.
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.
