In the 1990s, physicists Gerard 't Hooft and Leonard Susskind posited a hypothesis that shocked science and public opinion alike. It is known as the Holographic Principle and defends the idea that the universe can be interpreted as a hologram. What does that mean?
The problem with the holographic principle is that it uses a term that refers to a completely wrong idea: that our universe is really a hologram. From there, to think that what we experience is not real and ends up in the Matrix, there is very little, but it is not true. The universe is not a hologram, but perhaps it could be explained as one.
The holographic principle explains the force of gravity by encoding it in two dimensions, which would allow us to arrive at a universal model of physics and study phenomena that we currently do not understand from a completely new perspective.
Seriously considering the above argument, a possible conclusion is to raise this level to a fundamental principle, thus establishing that any theory that aspires to a candidate for quantum gravity must have a number of states limited by the exponential of the area of the region considered. So a particularly attractive solution emerges when considering that, perhaps what happens is that all the physics inside the box is completely described by a quantum system without gravity, but instead of occupying all three dimensions, it just lives on the surface of the box, thus saturating the proposed height. In this pictureTherefore, the three-dimensional world is a mere illusion, a hologram created by two-dimensional "pixels" whose complicated dynamics create the impression of the existence of new dimensions and gravity as emergent concepts. This exotic idea, proposed by Gerardus' t Hooft and Leonard Susskind, is known as the holographic principle, and its subsequent refinements have spearheaded quantum gravity research for the past two decades.
Naturally, these vague ideas did not take true form until, years later, Juan Maldacena proposed a concrete model in which this principle can be carried out with precision: the so-called AdS / CFT correspondence. Without going into the details of this model, we can draw a lesson from it that ties one last loose end in our thought experiment. In particular, if all the physics of our box is described by pixels at the edge, it seems fair to ask what the typical states of those pixels look like at different energies.
