While many know "negative energy" to refer to the negative chi, negative aura, or otherwise detrimental energy that a person gives off, the term also has a scientific definition. Based on the Heisenberg uncertainty principle, negative energy has to do with the inherent fluctuations in energy that exists in any energy or magnetic field. This form of "exotic matter" is a highly unpredictable force that has been proven to exist within the midst of fields of zero energy. Although difficult to identify, this type of energy is speculated to exist at the brink of black holes, and has been cited as a necessary prerequisite for time travel by Stephen Hawking.
The concept of negative energy was proposed by British physicist Paul Adrien Maurice Dirac in 1928, as a component of the Dirac equation. This equation was designed to be consistent to the standards of special relativity. In this equation, Dirac described how quantum states of positive energy would be offset by negative energy. Generally, these two types of energy will balance one another. Thus, a negative form of energy is not usually an observable phenomenon. However, in the instance of a pure vacuum, negative energy states will be expressed for all atoms within the vacuum while no positive energy states will be expressed. This concept is referred to as the Dirac sea.
Theoretically, a hole can develop in the Dirac sea if a stray gamma ray collides with electrons in a negative state of energy, thus converting it into a positively-charged electron. Such a hole in the Dirac sea would behave in the opposite way of the original, negatively-charged electron. The new positively-charged electron would be an example of antimatter. Thus, antimatter should not be confused with a negative state of energy.
In 1948, the Dutch physicist Hendrick Casimir predicted that a small attractive force could exist between two uncharged, parallel plates in a vacuum. Should the plates be resting extremely close to one another, negative energy is produced since the number of electromagnetic waves between the two plates becomes less than that of surrounding space. In essence, a negative state of energy becomes present when the wavelengths of particles in a certain region of space are less than what may normally be measured.
Casimir's predictions have been observed in two separate experiments. The first experiment occurred in 1958, and was overseen by M. J. Sparnaay. It produced results that were consistent with Casimir's theories. The second experiment, by Steve K. Lamoreaux, was conducted in 1997. Rather than using two plates in the experiment, Lamoreaux paired a single plate with another plate that was part of a nearly-precise sphere. This experiment also confirmed Casimir's predictions. While negative states of energy may not be observable, they have been proven both theoretically as well as by means of experiment.