Quantum mechanics and quantum field theory are both fundamental frameworks in modern physics, but they have different scopes and applications. While quantum mechanics provides a description of the behavior of particles on an individual level, quantum field theory extends this framework to describe the interactions of particles within a field.
There are several reasons why quantum mechanics continues to be used alongside quantum field theory in the physics community:
Applicability to different scales: Quantum mechanics is particularly well-suited for describing the behavior of particles on the microscopic scale. It successfully explains phenomena in atomic and molecular physics, solid-state physics, and many other areas. Quantum field theory, on the other hand, is typically applied to high-energy particle physics and the study of fundamental particles and their interactions. While there is overlap between the two frameworks, they are often used in different contexts.
Complexity and computational challenges: Quantum field theory is more mathematically and computationally involved compared to quantum mechanics. Calculations in quantum field theory often require advanced techniques such as perturbation theory, Feynman diagrams, and renormalization. These calculations can be computationally intensive and challenging, making quantum field theory less accessible for certain applications where quantum mechanics provides sufficient accuracy and simplicity.
Phenomenological models: Quantum mechanics provides a rich set of phenomenological models that have been extensively tested and verified experimentally. These models, such as the Schrödinger equation and the matrix mechanics formalism, offer accurate predictions for a wide range of systems. In many cases, quantum mechanics provides a practical and effective framework without the need to delve into the more complex formalism of quantum field theory.
Conceptual clarity: Quantum mechanics has a well-established and widely understood conceptual framework. It provides a clear and intuitive picture of quantum phenomena, including wave-particle duality, superposition, and quantum measurement. Quantum field theory, on the other hand, introduces additional concepts such as fields, particles, and vacuum fluctuations, which can be more abstract and challenging to grasp. As a result, quantum mechanics continues to be a preferred choice for pedagogical purposes and in many practical applications.
While quantum field theory provides a more comprehensive framework that unifies quantum mechanics and special relativity, its full application and understanding require a deeper level of mathematical and theoretical knowledge. Quantum mechanics remains a powerful and versatile tool in its own right, serving as the foundation for many branches of physics. The adoption of quantum field theory depends on the specific research area and the level of complexity required to address the physical phenomena under investigation.