One of the most intriguing theoretical predictions concerning black holes, objects with such a strong gravitational field that even light cannot escape them, is that they have nonzero entropy. The surface enclosing the region from which light cannot escape is called the event horizon, and the so-called Bekenstein-Hawking formula states that the entropy of a black hole is proportional to the area of its event horizon. When comparing this result to the Sackur-Tetrode equation for the entropy of a common physical system such as an ideal gas, one noticeable difference is that the entropy of an ideal gas is proportional to the number of particles distributed over the volume of the box that contains the gas, unlike the black hole entropy, which is proportional to the area of its event horizon. This suggests that all degrees of freedom of a gravitational system are somehow encoded on a boundary of the region enclosing it. This is what is meant by saying that gravity is holographic. One of the most precise formulations of this concept is given in the famous AdS/CFT correspondence, and one big part of our project is dedicated to exploring this challenging idea in cases where gravity possesses a geometrical feature known as torsion.
