In the theory of Loop Quantum Gravity (LQG), the underlying force that is responsible for the quantization of gravitational spacetime and the formation of spin networks is not a separate force in itself. Instead, LQG seeks to describe gravity itself, including the curvature of spacetime, in a quantum framework.
In LQG, spacetime is envisioned as a discrete structure rather than a smooth continuum. The fundamental building blocks of spacetime are known as "spin networks." These spin networks are graphs composed of interconnected nodes and edges, where the nodes represent elementary units of volume, and the edges represent quantum connections between these units.
The curvature of spacetime, which is traditionally described by General Relativity, arises in LQG as a result of the interconnections and interactions of these elementary units. The discrete geometric quantities associated with these spin networks, such as areas and volumes, are quantized, leading to a discrete and granular spacetime structure.
The quantization and curvature of spacetime in LQG are not described by an additional force acting on the singularities or loops. Rather, they emerge from the fundamental principles of the theory, which incorporate quantum mechanics and attempt to reconcile it with the gravitational field. The theory of LQG aims to provide a quantum description of gravity and the geometry of spacetime itself, without the need for additional forces beyond gravity.
It's worth mentioning that LQG is still an active area of research, and many aspects of the theory are still being developed and refined. While it offers intriguing possibilities for resolving the singularities of General Relativity and formulating a quantum theory of gravity, it is important to note that LQG is not yet a fully established and experimentally confirmed theory.