The question of whether everything is quantum is a topic of ongoing debate and investigation in physics and philosophy. While quantum theory is incredibly successful in describing the behavior of fundamental particles and their interactions, its applicability to macroscopic objects and everyday experiences is less straightforward.
At the fundamental level, quantum theory provides a mathematical framework that describes the behavior of particles and fields on the smallest scales. It introduces concepts such as wave-particle duality, superposition, and quantum entanglement. Quantum theory is necessary to accurately describe and predict the behavior of particles in certain regimes, such as in the microscopic world of atoms and subatomic particles.
However, the transition from the microscopic quantum realm to the macroscopic world is not fully understood. Macroscopic objects, such as tables, chairs, and even larger systems like planets and galaxies, appear to follow classical physics described by Newtonian mechanics or general relativity. These classical theories are effective in describing the behavior of macroscopic objects with high precision.
The challenge lies in understanding the boundary between the quantum and classical realms. This is an area of active research in quantum foundations and quantum decoherence. The process of decoherence refers to the loss of quantum coherence and the emergence of classical behavior due to interactions with the environment.
Quantum effects can become negligible and effectively "wash out" as systems become larger and more complex, leading to classical behavior. The transition from the quantum to the classical realm is often referred to as the "quantum-classical boundary" or the "measurement problem."
In summary, while quantum theory provides a fundamental framework to describe the behavior of particles and fields on small scales, the question of whether everything is fundamentally quantum or whether there is a clear boundary between the quantum and classical worlds is still a subject of investigation and scientific inquiry.