What is anti -gravity technology?

Answer 1

Anti-gravity technology is sometimes portrayed as technology able to make an object immune to gravity, but this concept in flawed.

It is not possible to shield an object from gravity (such as you might shield an object from an electric field), because everything that has energy (which basically means everything) 'feels' gravity. Also gravity is universally attractive so no cancellation can be made by using oppositely gravitationally charged particles.

Also any object shielded from gravity (assuming that this is possible) would not simply float above the ground. It would be flung away from the Earth since there is nothing keeping in achored to the Earth anymore, and the Earth moves around the Sun at a great speed. (Note that birds are still anchored to the Earth via gravity, so they are not thrown away.)

Instead what people tend to call anti-gravity technology is simply technology meant to counteract the force of gravity. For example if gravity pulls you downwards, you provide an equal force upwards. This can be done in many ways, using rockets, wings or even something as simply as someone lifting you.

A popular realisation of this are for example MagLev trains. These are trains which use electromagnetic forces to levitate a train above the track. Gravity still acts, but another force is simply provided to counteract it.