The minisuperspace in
physics
Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
, especially in theories of
quantum gravity
Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the v ...
, is an approximation of the otherwise infinite-dimensional
phase space
The phase space of a physical system is the set of all possible physical states of the system when described by a given parameterization. Each possible state corresponds uniquely to a point in the phase space. For mechanical systems, the p ...
of a
field theory.
The phase space is reduced by considering the largest
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
modes to be of the order of the size of the universe when studying
cosmological model
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fu ...
s and removing all larger modes.
The validity of this approximation holds as long as the
adiabatic approximation holds.
An example would be to only consider the scale factor and Hubble constant for a
Friedman–Robertson–Walker model in minisuperspace model the small true vacuum bubble which is nearly spherical with one single parameter of the scalar factor a is described as minisuperspace. It plays a significant role in the explanation of the origin of universe as a bubble in quantum cosmological theory.
References
Quantum gravity
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