Can someone explain in very basic terms the difference between these two?
In: Physics
The holographic principle is a statement about the structure of spacetime. Simulation theory, whatever you have in mind, most likely doesn’t tell you anything you don’t already know about spacetime. However, I think this question points to an interesting analogy that’s actually driven a lot of progress in AdS/CFT in recent years.
The analogy you might be thinking of might be something along the following lines. In the framework of holography, the geometry and dynamics of spacetime is fully encoded by the physics of a system on the boundary. One might say that in this sense, the boundary theory “simulates” the bulk system – the bulk is the program/software/simulation, the boundary the computer. This turned out surprisingly to be a really useful perspective, which I‘ll try to explain a bit now.
A basic observation is that the **boundary theory encodes information like a computer does**. Say you‘re interested in an apple you’re holding in your hand. In bulk theory your apple describes a little clump of energy localized near your hand. In the corresponding boundary description however, the information of your apple gets scrambled and smeared everywhere. This is like when you stare at an image of an apple on your screen, that image is localized as a clump of pixels at the center your screen but the instruction for producing that image is encoded in bits in your compute in an essentially incomprehensible way.
More generally, the bulk theory is something that (ideally) resembles the real world – much like how an image on your screen resembles the real world. The boundary theory on the other hand looks like a much simpler physical system in a lab – like switches and circuits in a compute that generate your image. And indeed it turned out to be useful in physics to ask questions about the *information theory* of the system on the boundary – as if it‘s a computational device encoding the data of the bulk it‘s “simulating”.
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