Quantum mechanics is a highly successful and comprehensive theory that has been tested and verified in a wide range of experiments. It provides a framework for understanding the behavior of particles and systems at the microscopic level, such as atoms and subatomic particles.
However, when it comes to predicting the behavior of macroscopic systems, such as everyday objects or large collections of particles, quantum mechanics becomes less relevant and classical physics, which includes Newtonian mechanics and electromagnetism, provides accurate predictions.
The transition from the quantum realm to the classical realm is known as the quantum-classical boundary or the quantum-classical divide. It arises due to a process called decoherence, in which the delicate quantum superpositions and entanglement of particles interact with their surrounding environment and become entangled with it. As a result, the quantum behavior is suppressed, and the system appears to behave classically.
Macroscopic systems typically have a large number of particles and interact strongly with their environment, causing their behavior to become effectively classical. For example, the position and momentum of macroscopic objects can be described with high precision using classical mechanics, without the need to invoke the probabilistic nature of quantum mechanics.
Therefore, for most practical purposes, the behavior of macroscopic systems can be accurately predicted using classical physics. Quantum mechanics is not typically required to describe or predict the behavior of everyday objects, as their quantum properties are negligible at macroscopic scales.
However, it's worth mentioning that there are ongoing debates and investigations into the boundary between the quantum and classical realms. Some researchers are exploring the possibility of observing quantum effects in larger systems or investigating the emergence of classical behavior from quantum principles. These studies often involve examining systems with specific properties or in highly controlled environments, but they do not challenge the overall validity of classical physics for macroscopic systems in our everyday experience.