Negative energy

Negative energy is a concept used in physics to explain the nature of certain fields, including the gravitational field and a number of quantum field effects.

In more speculative theories, negative energy is involved in wormholes which allow time travel and warp drives for faster-than-light space travel.

The strength of the gravitational attraction between two objects represents the amount of gravitational energy in the field which attracts them towards each other. When they are infinitely far apart, the gravitational attraction and hence energy approaches zero. As two such massive objects move towards each other, the motion accelerates under gravity causing an increase in the positive kinetic energy of the system. At the same time the gravitational attraction - and hence energy - also increase in magnitude. But the law of energy conservation requires that the net energy of the system does not change. This can only be resolved if the change in gravitational energy is negative, thus cancelling out the positive change in kinetic energy. Since the gravitational energy is getting stronger, this decrease can only mean that it is negative.

A universe in which positive energy dominates will eventually collapse in a "big crunch", while an "open" universe in which negative energy dominates will either expand indefinitely or eventually disintegrate in a "big rip". In the zero-energy universe model ("flat" or "Euclidean"), the total amount of energy in the universe is exactly zero: its amount of positive energy in the form of matter is exactly canceled out by its negative energy in the form of gravity.

Negative energies and negative energy density are consistent with quantum field theory.

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