[...] The maximal amount of energy that can be jammed into a sphere of the size R coincides with the mass of a black hole with radius R:
As a result, there is a maximum amount of information that can be crammed inside a sphere of the radius R, and this amount is proportional to
where Area is the surface area of a sphere with radius R and is a very tiny area called the Planck area.
This observation allows many people to think that maybe relevant degrees of freedom in physical problems involving gravitation actually live on a surface rather than in a volume - and that is where the term “holographic principle” comes from. Relevant degrees of freedom live on a surface, interact with each other there, and the 3d world we see is in a sense fiction - reflection of this dynamics on a surface.