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In quantum field theory, the Casimir effect (or Casimir force) [1] is a physical force acting on the macroscopic boundaries of a confined space which arises from the quantum fluctuations of a field. The term Casimir pressure is sometimes used when it is described in units of force per unit area.
Virtual photons can be classified into positive and negative virtual photons. These classifications are based on the direction of their energy and momentum and their contribution to the electromagnetic force. [2] If virtual photons exchanged between particles have a positive energy, they contribute to the electromagnetic force as a repulsive force.
The nuclear force is powerfully attractive between nucleons at distances of about 1 femtometre (fm, or 10 −15 metres), but it rapidly decreases to insignificance at distances beyond about 2.5 fm. At distances less than 0.7 fm, the nuclear force becomes repulsive.
Calculating the attractive or repulsive force between two magnets is, in the general case, a very complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets. The magnetic pole model does depend on some knowledge of how the ‘magnetic charge’ is distributed over the magnetic poles.
If, however, the universe contains dark energy, then the resulting repulsive force may be sufficient to cause the expansion of the universe to continue forever—even if >. [10] This is the case in the currently accepted Lambda-CDM model , where dark energy is found through observations to account for roughly 68% of the total energy content of ...
The force may be either attractive or repulsive. The problem is to find the position or speed of the two bodies over time given their masses , positions , and velocities . Using classical mechanics, the solution can be expressed as a Kepler orbit using six orbital elements .
(3), is the two-site two-electron Coulomb integral (It may be interpreted as the repulsive potential for electron-one at a particular point () in an electric field created by electron-two distributed over the space with the probability density ()), [a] is the overlap integral, and is the exchange integral, which is similar to the two-site ...
In this modified Dirac theory, Kowitt postulated that the positron is not a hole in the sea of electrons-with-negative-energy as in usual Dirac hole theory, but instead is a hole in the sea of electrons-with-negative-energy-and-positive-gravitational-mass: this yields a modified C-inversion, by which the positron has positive energy but ...