| Vacuum State |
Article Index for Vacuum |
Website Links For Vacuum |
Information AboutVacuum State |
| CATEGORIES ABOUT VACUUM STATE | |
| quantum field theory | |
|
If the quantum field theory can be accurately described through Perturbation Theory , then the properties of the vacuum are analogous to the properties of the Ground State of a quantum mechanical Harmonic Oscillator . In this case the Vacuum Expectation Value (VEV) of any Field Operator vanishes. For quantum field theories in which Perturbation Theory breaks down at low energies (for example, Quantum Chromodynamics or the BCS Theory of Superconductivity ) field operators may have non-vanishing Vacuum Expectation Value s called Condensate s. In the Standard Model , the non-zero vacuum expectation value of the Higgs Field , arising from Spontaneous Symmetry Breaking , is the mechanism by which the other fields in the theory acquire mass. In many situations, the vacuum state can be defined to have zero energy, although the actual situation is considerably more subtle. The vacuum state is associated with a Zero-point Energy , and this zero point energy has measurable effects. In the laboratory, it may be detected as the Casimir Effect . In Cosmology , the energy of the vacuum state appears as the Cosmological Constant . An outstanding requirement imposed on a potential Theory Of Everything is that the vacuum energy of the vacuum state must explain the physically observed cosmological constant. For a Relativistic field theory, the vacuum is Poincaré Invariant . Poincare invariance implies that only Scalar combinations of field operators have non-vanishing VEVs. The VEV may break some of the Internal Symmetries of the Lagrangian of the field theory. In this case the vacuum has less symmetry than the theory allows, and one says that Spontaneous Symmetry Breaking has occurred. |
|
|