Classical physics, which includes Newtonian mechanics and Maxwell's equations of electromagnetism, works well for describing the behavior of large or massive objects because it is based on macroscopic observations and simplified assumptions. These theories were developed before the advent of quantum mechanics and were successful in explaining the motion of planets, the behavior of fluids, and the interactions of everyday objects.
However, classical physics fails to accurately describe the behavior of small or sub-atomic entities due to several reasons:
Quantum Mechanics: At the sub-atomic scale, particles such as electrons and photons exhibit wave-particle duality, meaning they can behave both as particles and waves. Quantum mechanics, which was developed in the early 20th century, provides a more accurate framework for describing the behavior of these particles. It introduces probabilistic descriptions, uncertainty principles, and wave functions to account for the quantum nature of particles.
Uncertainty Principle: The Heisenberg uncertainty principle states that certain pairs of physical properties, such as position and momentum, cannot both be precisely determined simultaneously. This principle implies fundamental limitations on our ability to precisely know the properties of sub-atomic particles, and it is a consequence of the wave-like nature of particles.
Wave-Particle Duality: Quantum mechanics reveals that particles can exhibit wave-like behavior, such as interference and diffraction. This is in contrast to classical physics, which considers particles strictly as point-like objects. The wave-particle duality is a fundamental aspect of quantum mechanics and plays a crucial role in understanding the behavior of sub-atomic entities.
Quantum Interactions: Quantum mechanics introduces the concept of quantum interactions, which are fundamentally different from classical interactions. Quantum systems can be in a superposition of multiple states, and their interactions can lead to phenomena such as entanglement, where the properties of two or more particles become correlated in non-classical ways.
In summary, classical physics is an excellent approximation for describing macroscopic objects but fails to accurately describe the behavior of small or sub-atomic entities. Quantum mechanics provides a more comprehensive framework for understanding the probabilistic, wave-like nature of particles and their interactions at the quantum level. It is important to note that classical physics emerges as an approximation in situations where quantum effects can be neglected or average out, such as in macroscopic objects with a large number of particles.