Final answer:
If quantum physics is not applicable to macroscopic objects, this implies that the behavior of large-scale objects is accurately described by classical mechanics, and the peculiar quantum effects are negligible or undetected at that scale.
Step-by-step explanation:
If Quantum Physics is not applicable to macroscopic objects, this implies that the strange and often counterintuitive principles of quantum mechanics do not manifest in the behavior of large-scale objects that we can observe in the everyday world. Instead, the classical mechanics describe the motion and phenomena of macroscopic objects.
Niels Bohr's correspondence principle states that for large systems, quantum mechanics predictions must agree with those of classical mechanics. This is because the quantum properties that are significant at the atomic and subatomic levels become negligible at the macroscopic scale. In essence, quantum mechanics and classical mechanics are not competing theories but are complementary, with quantum mechanics describing both micro and macro world, while classical mechanics is a limit of quantum mechanics applicable at large scales.
This correspondence also means that features like wave-particle duality, which are essential to describe microscopic particles, do not have observable effects on the motion of macroscopic objects. The motion of macroscopic objects, such as chairs and baseballs, can be predicted with extremely high accuracy using classical physics without needing to consider quantum effects. For example, the wave properties suggested by the de Broglie wavelengths of macroscopic objects are immeasurably small and thus do not affect their motion in a way we can detect.