# From Coarse-Graining to Holography in Loop Quantum Gravity

## TL;DR

This paper explores how coarse-graining in loop quantum gravity relates to the holographic principle, proposing a way to reconstruct bulk states from boundary states through gauge equivalence, aiming to define holographic dynamics.

## Contribution

It introduces a novel approach linking coarse-graining, gauge invariance, and holography in loop quantum gravity, proposing a method to realize Hamiltonian constraints as gauge reductions.

## Key findings

- Boundary states can be reconstructed from bulk states with a single vertex and loop.
- Proposes gauge equivalence as a means to implement Hamiltonian constraints.
- Establishes a potential one-to-one correspondence between physical states and boundary states.

## Abstract

We discuss the relation between coarse-graining and the holographic principle in the framework of loop quantum gravity and ask the following question: when we coarse-grain arbitrary spin network states of quantum geometry, are we integrating out physical degrees of freedom or gauge degrees of freedom? Focusing on how bulk spin network states for bounded regions of space are projected onto boundary states, we show that all possible boundary states can be recovered from bulk spin networks with a single vertex in the bulk and a single internal loop attached to it. This partial reconstruction of the bulk from the boundary leads us to the idea of realizing the Hamiltonian constraints at the quantum level as a gauge equivalence reducing arbitrary spin network states to one-loop bulk states. This proposal of "dynamics through coarse-graining" would lead to a one-to-one map between equivalence classes of physical states under gauge transformations and boundary states, thus defining holographic dynamics for loop quantum gravity.