3.2 The Gauge/Gravity Duality

summary

If we consider a set of boxes, we would intuitively expect the amount of information we could store inside to scale with the volume of the boxes.

However, with enough gravity, the set of boxes will collapse into a black hole.
The information stored in a black hole scales with its surface area.
We know that black holes are the most entropic objects in the universe.
This gives rise to the Holographic Principle, which states that all of the information within a three dimensional system can be represented on a two dimensional surface.

A ‘duality’ is a situation in which the same physical reality can have several different descriptions.

The Gauge/gravity duality, also known as the AdS/CFT correspondence, states that string theory is equivalent to gauge theory, a non-gravitational quantum field theory.
String theory describes the ‘bulk’ of the universe, while gauge theory describes what happens at the ‘boundary’.
Because the two descriptions live in different numbers of dimensions, we call such a correspondence holographic.
The extra bulk dimension can be encoded in a scale size along the boundary.

Over ten thousand papers have been published that reference the original gauge/gravity duality paper.

The gauge/gravity duality theory has been used to describe systems ranging from micro Kelvin atoms to quark-gluon plasmas with temperatures of several trillion Kelvins.
It has enabled physicists to study strongly interacting field theory by working with higher-dimensional gravity.
This study of field theory has in turn enabled physicists to study quantum gravity.

Of all known systems, black holes are the...