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...

- Simplest in terms of their mathematical description
- Closest to an ideal fluid
- Most efficient at storing information
- Fastest to reach equilibrium
- Fastest to scramble information
- Fastest computers