The reconciliation of "locality" in Quantum Field Theory (QFT) with the non-locality of Quantum Mechanics (QM) as described by Bell's theorem is a challenging and ongoing topic of research in the field of quantum foundations.
Bell's theorem demonstrates that certain correlations observed in entangled quantum systems cannot be explained by any theory that relies on local hidden variables. In other words, it suggests that the predictions of quantum mechanics violate the principle of locality, which states that events in one region of space cannot instantaneously affect events in another distant region.
Quantum Field Theory, on the other hand, is a framework that combines quantum mechanics and special relativity, and it is based on the concept of local interactions. In QFT, fields exist at every point in spacetime, and particles are excitations of these fields. The theory is constructed to respect relativistic causality, where information and interactions propagate at or below the speed of light.
Reconciling these two seemingly contradictory aspects is an active area of research and has led to various proposed solutions and interpretations. Here are a few approaches that have been explored:
Loopholes in Bell's theorem: Some researchers have examined potential loopholes in Bell's theorem that may allow for local explanations of the observed correlations. These include assumptions of free will, hidden variables, or the presence of uncontrolled influences. However, experimental tests of Bell's theorem have significantly constrained these loopholes, making it difficult to explain the observed violations of locality.
Non-locality as an emergent property: Some theoretical frameworks propose that non-locality arises as an emergent property in certain quantum systems or from underlying structures. For instance, entanglement could be viewed as a form of non-local correlation that arises from a deeper level of reality. These approaches aim to provide a consistent framework where locality emerges at larger scales while allowing for non-local behavior at the microscopic level.
Information causality: Another approach is to explore the concept of information causality, which considers that the transfer of information is limited by the speed of light. While this doesn't fully resolve the non-local aspects of quantum mechanics, it suggests that the transmission of classical information between distant regions is limited, even though quantum entanglement can still exhibit non-local correlations.
It's important to note that the resolution of the tension between locality and non-locality in quantum mechanics is an active area of research and remains an open question. Different interpretations and approaches continue to be explored, and there is ongoing debate and investigation to deepen our understanding of these fundamental aspects of quantum theory.