Holographic principle

The holographic principle is a speculative conjecture by G. d't Hooft of quantum gravity theories that all of the information contained in a volume of space can be represented by a theory that lives in the boundary of that region. In other words, if you have a room then you can model all of the events within that room by creating a theory that only takes into account the what happens in the walls of the room. The holographic principle also states that at most there is one degree of freedom per Planck area in that theory.