Negative energy

Negative energy is a concept used in physics to explain the nature of certain fields, including the gravitational field and various quantum field effects. Negative energy is a concept used in physics to explain the nature of certain fields, including the gravitational field and various quantum field effects. In more speculative theories, negative energy is involved in wormholes which may allow for 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 approach 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 not change. This issue 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 cancelled out by its negative energy in the form of gravity. Negative energies and negative energy density are consistent with quantum field theory. In quantum theory, the uncertainty principle allows the vacuum of space to be filled with virtual particle-antiparticle pairs which appear spontaneously and exist for only a short time before, typically, annihilating themselves again. Some of these virtual particles can have negative energy. Their behaviour plays a role in several important phenomena, as described below. In the Casimir effect, two flat plates placed very close together restrict the wavelengths of quanta which can exist between them. This in turn restricts the types and hence number and density of virtual particle pairs which can form in the intervening vacuum and can result in a negative energy density. This causes an attractive force between the plates, which has been measured. Virtual particles with negative energy can exist for a short period. This phenomenon is a part of the mechanism involved in Hawking radiation by which black holes evaporate. It is possible to arrange multiple beams of laser light such that destructive quantum interference suppresses the vacuum fluctuations. Such a squeezed vacuum state involves negative energy. The repetitive waveform of light leads to alternating regions of positive and negative energy.