No, quantum field theory (QFT) has not completely replaced quantum mechanics in the physics world. Quantum mechanics and quantum field theory are both important frameworks for describing the behavior of particles and fields at the quantum level, but they have different scopes and applications.
Quantum mechanics is a fundamental theory that describes the behavior of individual particles, such as electrons or photons, as quantum objects. It provides a mathematical framework to calculate the probabilities of various outcomes when measuring properties like position, momentum, and energy of particles. Quantum mechanics is incredibly successful and forms the foundation of many areas of physics, including atomic and molecular physics, condensed matter physics, and quantum information theory.
Quantum field theory, on the other hand, extends the principles of quantum mechanics to fields, which are pervasive throughout space and time. In QFT, particles are described as excitations or quanta of these fields. This framework is particularly useful for describing the behavior of particles in high-energy physics, such as elementary particles and their interactions. Quantum field theory is essential for understanding phenomena in particle physics and is a key component of the Standard Model, which describes the electromagnetic, weak, and strong nuclear forces.
While quantum field theory incorporates quantum mechanics, it does not render it obsolete. Quantum mechanics is still used in many areas of physics where the effects of fields are not dominant, such as the behavior of individual atoms or molecules. Additionally, quantum field theory can be mathematically challenging and is typically introduced at more advanced levels of study, while quantum mechanics remains a fundamental part of physics education.
In summary, quantum field theory has not replaced quantum mechanics in the physics world. Both frameworks are valuable and are used in different contexts to understand the behavior of particles and fields at the quantum level.