I can provide you with an overview of the three theories you mentioned: string theory, M-theory, and loop quantum gravity (LQG).
String Theory: String theory is a theoretical framework that suggests that fundamental particles are not point-like objects but rather tiny, vibrating strings. It attempts to reconcile quantum mechanics and general relativity and is often considered a candidate for a theory of everything. String theory has different variants, such as Type I, Type IIA, Type IIB, heterotic SO(32), and heterotic E8×E8. However, it has not yet been experimentally confirmed, and there is ongoing debate about its predictive power and testability.
M-Theory: M-theory is an extension of string theory that attempts to unify various versions of string theory into a single framework. It incorporates 11 dimensions (compared to the 10 dimensions of traditional string theory) and includes not only strings but also other higher-dimensional objects called "branes." M-theory is still an area of active research, and many aspects of it are not fully understood. It is considered by some researchers as a potential candidate for a theory of everything, but definitive experimental evidence or a complete understanding is still lacking.
Loop Quantum Gravity (LQG): Loop quantum gravity is an approach to quantum gravity that seeks to describe the fundamental nature of space and time at the quantum level. It proposes that space is composed of tiny, discrete units called "loops" or "spin networks." LQG attempts to reconcile general relativity with quantum mechanics without the need for strings or extra dimensions. While loop quantum gravity offers a different perspective from string theory, it is also a subject of ongoing research and does not yet provide a complete and widely accepted theory of everything.
It is important to note that the nature of a theory of everything and its acceptance in the scientific community is still a subject of active research and debate. At present, there is no consensus on which theory, if any, is the correct description of the fundamental nature of the universe. Scientists continue to explore these theories, conduct experiments, and seek further evidence to evaluate their validity.