False vacuum

False vacuum: The false vacuum is a peculiar form of matter which is predicted to exist by many (probably most) current theories of elementary particles. Particle physicists describe the false vacuum, like all forms of matter, in terms of fields. Originally the phrase "false vacuum" was used to describe a region in which one or more fields have a set of values that do not minimize the energy density, but which are in a local valley of the energy density diagram. Classically such a state would be absolutely stable, since there would be no energy available for the fields to jump over the hills that surround the valley. By the rules of quantum theory, however, the fields can tunnel through the hill of the energy density diagram and settle eventually in the true vacuum, the state of lowest energy density. The false vacuum is nonetheless metastable, and in fact it can endure for a period which is long by early universe standards. The false vacuum has a negative pressure which creates a repulsive gravitational field, capable of driving the universe into a period of exponential expansion called inflation. Similar effects occur if the fields are at the top of a broad plateau, instead of in a valley, so in this book I have stretched the phrase "false vacuum" to include this case as well.