Anti-gravity

Anti-gravity is the concept of a force that would exactly oppose the force of gravity. Anti-gravity does not refer to either the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism, aerodynamic lift, or ion-propelled "lifters", which fly in the air by moving air with electromagnetic fields. Historically, anti-gravity was considered a possibility after the discovery of antimatter. Once the nature of antimatter was more clearly established, it was clear that gravity works the same for both matter and antimatter. Experimental measurements rule out repulsion between antihydrogen and the mass of the Earth. Under the current laws of physics, anti-gravity is not possible without some form of exotic matter such as negative mass (which has never been observed). Anti-gravity is a recurring concept in science fiction.