Quantum mechanics, as currently understood, is primarily formulated to describe the behavior of microscopic particles, such as atoms and subatomic particles. At the macroscopic scale, classical mechanics, which is a branch of physics that predates quantum mechanics, provides an excellent description of everyday objects like balls, sand grains, and larger systems.
Macroscopic objects consist of an enormous number of particles, and their behavior can be effectively described using classical mechanics due to a principle known as the correspondence principle. This principle states that the predictions of quantum mechanics converge to the predictions of classical mechanics as the number of particles involved becomes large. In other words, macroscopic objects exhibit behaviors that are consistent with classical physics, as quantum effects tend to average out at larger scales.
While quantum mechanics may not be necessary to describe the macroscopic behavior of objects, it still underlies the fundamental nature of matter and energy. The macroscopic world emerges from the underlying quantum mechanical properties of its constituents. The principles of quantum mechanics govern the behavior of the atoms and particles that make up macroscopic objects, even if those objects themselves can be well-described by classical mechanics.
It is important to note that there are some areas of research where quantum effects on macroscopic scales are being explored, such as quantum optics, superconductivity, and quantum coherence in large molecules. These areas investigate phenomena where macroscopic objects may exhibit quantum-like behaviors or are engineered to manifest quantum properties. However, these situations typically involve carefully controlled experimental conditions or highly specialized systems, rather than everyday macroscopic objects.