According to Loop quantum gravity (LQG), loops are the quantum excitations of the gravitational

field and they are space. Because there is no background space. Only loops over loops and these loops intersect each other just like a net. Interesting fact is that, the points at which loops intersect, i mean at the nodes “quanta of space” ( also called elements of space or grains of space)was found! Two adjacent quanta or elements of space are separated by a surface, and the area of this surface is also quantized. Nodes carry quantum numbers of volume elements and links carry quantum numbers of area elements. These quantum numbers and their algebra looked like the spin angular momentum numbers of elementary particles. So they are called spin network.

Here are few selected articles which should work well to understand spin network.

- “Loop Quantum Gravity“, by Carlo Rovelli ( For conceptual understanding read the article)
- “ A Spin Network Primer“, by Seth A. Major [suitable for students of advanced quantum mechanics (undergraduate)]
- “Loop Quantum Geometry: A primer “ , by Alejandro Corichi
- “Spin Networks and Quantum Gravity” by Carlo Rovelli, Lee Smolin
- “Spin networks in nonperturbative quantum gravity” by John Baez
- “Diffeomorphism-Invariant Spin Network States” by John Baez

**Useful articles for Quantum Mechanics :**