Particles are quantized excitations of fields from "summary" of The Quantum Theory of Fields by Steven Weinberg,Weinberg S
Quantum field theory is a theoretical framework that combines the principles of quantum mechanics with the concepts of fields. In this framework, particles are viewed as quantized excitations of these fields. This means that the fields themselves are the fundamental entities, and particles are simply specific manifestations or vibrations of these fields. Each type of particle corresponds to a specific field, which permeates all of spacetime. For example, the electromagnetic field corresponds to photons, the particles that carry the electromagnetic force. Similarly, the electron field corresponds to electrons, the fundamental particles of matter. By quantizing these fields, we can understand the discrete and quantized nature of particle properties, such as energy and momentum. In classical field theory, fields are continuous and can take on any value at each point in spacetime. However, in quantum field theory, these fields are quantized, meaning they can only have certain discrete values. These quantized values correspond to the energy levels of the particles associated with the field. When a field is in its lowest energy state, it corresponds to the vacuum state, which is not necessarily empty but rather filled with quantum fluctuations. Excitations of the field above this vacuum state correspond to particles with specific properties such as mass, charge, and spin. The process of quantizing a field involves promoting the field to an operator that acts on a quantum state. This allows us to describe the creation and annihilation of particles as the field operators acting on the vacuum state. The interactions between particles are then described by how these field operators interact with each other. By treating particles as quantized excitations of fields, quantum field theory provides a unified framework for understanding the fundamental forces and particles of the universe. This approach has been highly successful in predicting and explaining a wide range of phenomena, from the behavior of subatomic particles to the structure of the cosmos.
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