Anti-gravity

Transcript

1. Anti-gravity
   

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2. Anti-gravity is the idea of creating a place or object that is free
   from the force of gravity.
   

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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.
   

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4. Anti-gravity is a recurring concept in science fiction, particularly in
   the context of spacecraft propulsion.
   

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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.
   

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6. Under general relativity, anti-gravity is IMPOSSIBLE except under
   contrived circumstances
   

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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.
   

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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.
   

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9. The Institute for Gravity Research of the Göde Scientific
   Foundation has tried to reproduce different experiments which
   allegedly show an antigravity effect.
   

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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.
    

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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.
    

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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.
    

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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.
    

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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.
    

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