Quantum fields are fundamental entities in quantum field theory, a framework that combines quantum mechanics with special relativity. They are not made up of any other particles or constituents. Rather, quantum fields are the underlying mathematical structures that describe the behavior and interactions of particles.
In quantum field theory, every type of particle is associated with a specific quantum field. For example, there is an electron field, a photon field, a quark field, etc. These fields permeate all of space and time. Each field has associated excitations called particles, which can be created or annihilated in interactions.
Quantum fields are not directly observable, but their effects can be measured through interactions with particles. For example, the strength and nature of the interactions between particles are described by the properties of the respective quantum fields.
Regarding the formation of quantum fields, they are considered to be fundamental and have existed since the early moments of the universe. Quantum field theory is a fundamental framework used to describe the behavior of particles and their interactions across all scales, from subatomic particles to the largest cosmological structures. However, it is important to note that our current understanding of the universe suggests that the nature of quantum fields and the laws governing them may have evolved or changed during significant cosmic events, such as the early moments of the Big Bang or during phase transitions in the early universe.