Quantum mechanics is indeed considered one of the most fundamental branches of physics. It provides a framework for understanding the behavior of particles at the microscopic scale and has been highly successful in describing a wide range of phenomena. Quantum mechanics is based on principles of wave-particle duality, superposition, and probabilistic measurements.
While quantum mechanics is foundational to understanding the behavior of particles, it is important to note that it is not the sole basis of all reality. The laws of classical physics, such as Newtonian mechanics and general relativity, are still valid and applicable in many everyday situations and at macroscopic scales. Classical physics provides accurate descriptions of the motion of everyday objects, the behavior of planets, and the mechanics of macroscopic systems.
However, at the microscopic level, where the behavior of particles and interactions between them are involved, quantum mechanics becomes indispensable. It is the basis for understanding the behavior of atoms, subatomic particles, and the fundamental forces of nature.
That said, it is important to recognize that there are unresolved questions and areas where quantum mechanics and classical physics do not easily reconcile, such as the unification of general relativity and quantum mechanics (quantum gravity). Additionally, the macroscopic world emerges from the microscopic quantum realm through processes known as quantum decoherence and the correspondence principle, but the exact mechanisms and the boundary between quantum and classical domains are still topics of investigation.
In summary, while quantum mechanics provides a fundamental framework for understanding the behavior of particles and is crucial for describing the microscopic world, classical physics remains valid and applicable at macroscopic scales. The interplay between quantum and classical physics shapes our understanding of the diverse phenomena observed in the universe.