Anti-gravity

Transcript

1. Anti-gravity
2. Anti-gravity is the idea of creating a place or object that is free from the force of gravity.
3. It does not refer to 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 or aerodynamic lift.
4. Anti-gravity is a recurring concept in science fiction, particularly in the context of spacecraft propulsion.
5. In Newton's law of universal gravitation, gravity was an external force transmitted by unknown means. In the 20th century, Newton's model was replaced by general relativity where gravity is not a force but the result of the geometry of spacetime.
6. Under general relativity, anti-gravity is IMPOSSIBLE except under contrived circumstances
7. Quantum physicists have postulated the existence of gravitons, a set of massless elementary particles that transmit the force, and the possibility of creating or destroying these is unclear.
8. "Anti-gravity" is often used colloquially to refer to devices that look as if they reverse gravity even though they operate through other means, such as lifters, which fly in the air by using electromagnetic fields.
9. The Institute for Gravity Research of the Göde Scientific Foundation has tried to reproduce different experiments which allegedly show an antigravity effect.
10. All attempts to observe an antigravity effect have been unsuccessful. The foundation has offered a reward of one million euros for a reproducible antigravity experiment.
11. mimicking anti-gravity effect (1) Magnetic levitation suspends an object against gravity by use of electromagnetic forces. While visually impressive, gravitation itself functions normally in such devices. Various alleged anti- gravity devices may in reality work by electromagnetism.
12. mimicking anti-gravity effect (2) 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. Equivalently, 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.
13. mimicking anti-gravity effect (3) 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.
14. mimicking anti-gravity effect (4) Ionocraft, sometimes referred to as "Lifters", have been claimed to defy gravity, but in fact they use accelerated ions which have been stripped from the air around them to produce thrust. The thrust produced by one of these devices is not enough to lift its own power supply. Specifically, a special type of electrohydrodynamic thruster uses the Biefeld–Brown effect to hover.