The claim that macroscopic objects have quantum nature but their quantum effects are essentially ignorable stems from the concept of decoherence. Decoherence refers to the phenomenon where a quantum system, when interacting with its environment, loses its quantum coherence and behaves more like a classical system. It is a process that leads to the suppression of quantum interference and the emergence of classical-like behavior.
In macroscopic objects, such as everyday objects we encounter in our daily lives, the interactions with their surrounding environment are extremely complex and occur on a large scale. These interactions result in the rapid entanglement of the object's quantum state with the environment, leading to decoherence.
Decoherence effectively washes out the quantum behavior of macroscopic objects, making their behavior statistically well-described by classical physics. The quantum effects become negligible and average out over many particles or measurements, giving rise to the appearance of classical behavior.
While macroscopic objects can still exhibit some residual quantum effects, such as superconductivity or superfluidity, these effects are typically confined to highly controlled and specialized environments. In most everyday situations, the macroscopic objects we encounter can be adequately described using classical physics because their quantum behavior is effectively "hidden" or "masked" by the overwhelming influence of their environment.
It is important to note that the claim that macroscopic objects are fundamentally quantum in nature but exhibit classical behavior is still a topic of ongoing research and debate among physicists. Some interpretations of quantum mechanics, such as many-worlds interpretation or objective collapse theories, propose different perspectives on the nature of macroscopic objects and the boundary between the quantum and classical realms. The field of quantum foundations aims to investigate these fundamental questions regarding the nature of reality at different scales.