Classical mechanics and quantum physics are distinct theories that describe the behavior of physical systems at different scales. While classical mechanics is highly successful in describing the macroscopic world, it is not sufficient to explain phenomena that occur at the microscopic level, where quantum mechanics becomes necessary.
Quantum mechanics is the branch of physics that deals with the behavior of particles at the atomic and subatomic levels. It introduces concepts such as wave-particle duality, superposition, and quantum entanglement, which are not accounted for in classical mechanics. Quantum mechanics provides a probabilistic description of the behavior of particles, where quantities like position and momentum are represented by wavefunctions, and measurements give probabilities of obtaining particular outcomes.
However, classical mechanics can emerge as an approximation in certain circumstances when quantum effects can be neglected or when systems are large and their quantum behavior is averaged out. This is known as the correspondence principle. In the macroscopic limit, classical mechanics is an excellent approximation for describing the behavior of objects, as quantum effects become negligible.
It's important to note that quantum mechanics encompasses classical mechanics as a special case but extends its description to the microscopic realm. Therefore, classical mechanics can be seen as a limiting case of quantum mechanics, applicable when the quantum behavior becomes insignificant compared to the macroscopic scale of observation.
In summary, classical mechanics and quantum mechanics are separate theories that are applicable in different domains. Classical mechanics can be seen as an approximation of quantum mechanics in certain limits, but it cannot fully account for the phenomena observed at the quantum level.