In quantum field theory (QFT), the fact that fields respond instantly to certain changes or interactions, such as entanglement, is related to the concept of non-locality. Non-locality refers to the idea that the effects of a change in one part of a quantum system can be immediately observed or measured in another distant part of the system, without any delay or communication between them.
This non-local behavior arises due to the nature of quantum entanglement, which is a fundamental feature of quantum mechanics. When two or more particles become entangled, their quantum states become correlated in such a way that the state of one particle cannot be described independently of the state of the other(s). This entanglement can occur between particles that are separated by large distances.
In QFT, particles are described by quantum fields, which permeate all of space. These fields are quantum mechanical entities that can exhibit the phenomenon of entanglement. When two quantum fields become entangled, the entanglement can extend over a large region of space, potentially encompassing the entire system described by those fields.
The instantaneous response of fields to entanglement or other interactions is a consequence of the underlying mathematical formalism of QFT, which involves the concept of field operators and their commutation or anti-commutation relations. These mathematical relations allow for the non-local behavior observed in quantum systems.
Regarding the nature of such fields and why they respond globally, QFT does not provide a complete understanding of the fundamental nature of fields or the mechanisms behind their global responses. It is a mathematical framework that successfully describes the behavior of quantum systems, but it does not necessarily address the underlying "why" questions of the physical world. The nature of quantum fields and their non-local behavior is still an active area of research and exploration in theoretical physics.