Loop Quantum Gravity (LQG) and String/M-theory are two different approaches to a theory of quantum gravity, attempting to unify general relativity (which describes gravity on a large scale) with quantum mechanics (which describes the behavior of particles on a small scale). While both theories are still under development and lack experimental confirmation, they have distinct characteristics that make some people find LQG more promising than String/M-theory. Here are a few reasons why LQG is sometimes favored:
Background independence: LQG is built on the principle of background independence, which means that the theory does not rely on a pre-existing spacetime background. It treats spacetime as a dynamic entity that emerges from fundamental quantum structures. This feature is appealing because it aligns with the spirit of general relativity, where the geometry of spacetime is influenced by matter and energy.
Discrete spacetime: LQG suggests that spacetime is fundamentally discrete, meaning it consists of discrete building blocks or "atoms" of spacetime. This discretization helps to avoid singularities, such as those encountered in the mathematical formulation of general relativity. It provides a way to describe the fabric of spacetime at extremely small scales.
Quantum geometry: LQG employs the concept of quantum geometry, using mathematical tools from loop quantum gravity to describe the structure of spacetime on a microscopic scale. This approach attempts to quantize the geometry itself, treating lengths, areas, and volumes as discrete quantities subject to quantum laws.
Compatibility with quantum mechanics: LQG aims to reconcile general relativity with quantum mechanics in a more direct manner. It emphasizes a canonical quantization approach, which is based on principles similar to those of quantum mechanics. This compatibility with quantum mechanics may make it easier to incorporate other fundamental forces and particles into the theory.
It's worth noting that both LQG and String/M-theory are still active areas of research, and it is too early to determine which theory, if any, will ultimately prove to be the most successful in describing a complete theory of quantum gravity. The choice between the two theories often comes down to personal preference, the problem at hand, and the specific research interests of individual physicists.