The quest for a "Theory of Everything" that unifies general relativity (GR) and quantum mechanics (QM) is an ongoing challenge in theoretical physics. While it is an active area of research, no complete and fully validated Theory of Everything currently exists. However, I can provide some insights into your questions.
If a Theory of Everything were discovered—an equation or framework that successfully incorporates both GR and QM—it would be a significant scientific achievement. It would provide a comprehensive description of the fundamental forces and particles in the universe, allowing us to understand the behavior of matter and energy at all scales. This unified theory would encompass the macroscopic realm of gravity (described by GR) and the microscopic realm of quantum mechanics.
Regarding the origin of such a theory, there are various possibilities that scientists explore, beyond the idea of multiverses:
Mathematical elegance: Some physicists believe that the laws of nature possess inherent mathematical beauty and simplicity. They argue that a Theory of Everything should be elegant and possess mathematical properties that hint at its fundamental truth. This line of thinking seeks to find a theory that is compelling from a purely mathematical standpoint.
Symmetry and principles: Symmetry plays a fundamental role in modern physics, and many physicists search for theories that exhibit symmetries and obey certain fundamental principles. The search for a Theory of Everything often involves looking for symmetries, conservation laws, and fundamental principles that govern the behavior of matter and energy.
Fundamental building blocks: Another approach is to identify the most fundamental building blocks of the universe. This idea suggests that a Theory of Everything would describe the behavior of these fundamental entities and how they interact. String theory, for example, posits that tiny vibrating strings are the fundamental building blocks of matter and that their interactions give rise to the known particles and forces.
It's important to note that the loop of theorizing doesn't necessarily stop at finding a Theory of Everything. Scientific inquiry is an ongoing process, and even if a unifying theory is discovered, there will still be room for further exploration and refinement. New questions and phenomena may arise that require deeper understanding and refinement of the theory.
Science constantly evolves, and as new observations, experiments, and insights emerge, our understanding of the universe deepens. The quest for a Theory of Everything is part of this ongoing scientific journey, where theories are developed, tested, modified, and expanded upon to better explain the workings of the cosmos.