Bousso's holographic bound
Encyclopedia
A simple generalization of the Black Hole entropy bound (cf. holographic principle
) to generic systems is that, in quantum gravity
, the maximum entropy
which can be enclosed by a spatial boundary is given by a quarter of its surface area. However, as a general rule, this simple generalization appears to be false, because the spatial boundary can be taken to be within the event horizon
of a black hole. It also fails in cosmological models.
Raphael Bousso
came up with a modification that the spatial boundary should not be a trapped surface. This lead him to come up with Bousso's holographic bound, also known as the covariant entropy bound. Basically, a spatial boundary is valid if, when you consider both null sheets orthogonal to its tangent space, the expansion factor both point in the same direction. This defines inside and outside. The entropy of the interior region is bounded by the surface area of the boundary.
Holographic principle
The holographic principle is a property of quantum gravity and string theories which states that the description of a volume of space can be thought of as encoded on a boundary to the region—preferably a light-like boundary like a gravitational horizon...
) to generic systems is that, in quantum gravity
Quantum gravity
Quantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...
, the maximum entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
which can be enclosed by a spatial boundary is given by a quarter of its surface area. However, as a general rule, this simple generalization appears to be false, because the spatial boundary can be taken to be within the event horizon
Event horizon
In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...
of a black hole. It also fails in cosmological models.
Raphael Bousso
Raphael Bousso
Rafael Bousso is a theoretical physicist and string theorist. Currently he is a professor at Department of Physics, UC Berkeley. He is known for the proposal of Bousso's holographic bound, also known as the covariant entropy bound.-Career:...
came up with a modification that the spatial boundary should not be a trapped surface. This lead him to come up with Bousso's holographic bound, also known as the covariant entropy bound. Basically, a spatial boundary is valid if, when you consider both null sheets orthogonal to its tangent space, the expansion factor both point in the same direction. This defines inside and outside. The entropy of the interior region is bounded by the surface area of the boundary.