Vacuum energy is the energy that exists in an "empty" piece of space. Quantum field theory considers the vacuum ground state not to be completely empty, but to consist of a seething mass of virtual particles and fields. Some believe that vacuum energy might be "dark energy", represented by the "cosmological constant" (λ) in general relativity or possibly something called "Quintessence". The cosmological constant, as most grand unified theoryies state, predicts a non-zero constant from the energy of vacuum fluctuations.
In vacuum energy, the fact that and area of the field of space is represented by a probability distribution and, since these fields do not have a permanent existence, they are called "vacuum fluctuations". Vacuum energy also causes changes in the magnetics. One example is the Casimir effect in which two metal plates reduces the vacuum energy between them, thereby creating a measurable force.
Another magnetic example is the accelerating universe in which the expansion of the universe appears to be increasing and is driven by the vacuum energy released as space expands. Vacuum energy is thought to be similar to the negative force of gravity. In 1934, Georges Lemaître interprets the cosmological constant as due to a vacuum energy with an unusual perfect fluid equation of state.
In 1973, Edward Tryon proposes that the universe may be a large scale quantum mechanical vacuum fluctuation where positive mass-energy is balanced by negative gravitational potential energy. Inflation is the idea—first proposed by Alan Guth (1981)—that the nascent universe passed through a phase of exponential expansion that was driven by a negative vacuum energy density (positive vacuum pressure). During the 1980s, there was many attempts to relate the field that generates the vacuum energy to specific fields that were predicted by Grand Unified Theories or to use observations of the universe to constrain those theories. These efforts produced a null-result and the exact nature of the particle or field that generates the vacuum energy density for inflation (the "inflaton") remains a mystery.
Vacuum energy has a number of consequences. Vacuum fluctuations are always created as a pair of fields. Examining normal physical processes with knowledge of these field phenomena can lead to interesting insight in electrodynamics. During discussions of perpetual motion, the topic of vacuum energy usually encourages serious inquiries.
See also: Magnetic flux, Virtual particle
