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.
Contents
- Gravitational energy
- Quantum field effects
- Casimir effect
- Squeezed light
- Hawking radiation
- Fractal physics
- Wormholes
- Warp drive
- References
In more speculative theories, negative energy is involved in wormholes which allow time travel and warp drives for faster-than-light space travel.
Gravitational energy
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.
Quantum field effects
Negative energies and negative energy density are consistent with quantum field theory.
Casimir effect
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.
Squeezed light
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.
Hawking radiation
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.
Fractal physics
Fractal physics theory is based on the idea of scale-invariance, that a phenomenon may be fundamentally the same whether viewed on a cosmic scale or at a subatomic scale. Specifically, it extends the two special relativity postulates to scale. The first postulate assumes that the absolute uniform scale cannot be detected, the second that the speed c of electromagnetic radiation photons in vacuum is independent of scale.
Fractal physics theory requires the presence of both negative and positive energies.
Wormholes
Negative energy appears in the speculative theory of wormholes. A wormhole directly connects two locations which may be separated arbitrarily far apart in both space and time, and in principle allows near-instantaneous travel between them.
Warp drive
A theoretical principle for a faster-than-light (FTL) warp drive for spaceships has been suggested, involving negative energy. It comprises a solution to Einstein's equations of general relativity, in which a bubble of spacetime is moved rapidly by expanding space behind it and shrinking space in front of it.