The compatibility of the Many-Worlds Interpretation (MWI) with Quantum Field Theory (QFT) is a topic of ongoing debate among physicists. While it is not accurate to say that MWI is inherently incompatible with QFT, there are challenges and open questions when trying to combine the two frameworks.
MWI suggests that the wave function, which describes the state of a quantum system, never collapses, but instead branches into multiple distinct branches corresponding to different outcomes of a measurement. In this interpretation, each branch represents a different "world" or "timeline" in which a different outcome of the measurement occurs. This approach allows for the existence of a multitude of parallel universes.
In the context of QFT, the wave function is replaced by a quantum field, and particles are viewed as excitations of these fields. QFT is a powerful framework that successfully describes the behavior of particles and fields, incorporating both quantum mechanics and special relativity. However, it is primarily formulated in terms of a single universe, and it is not immediately clear how to extend it to incorporate the branching of multiple universes as proposed by MWI.
One challenge is related to the interpretation of the quantum field itself. In MWI, the branching of universes implies that all possible outcomes of a measurement occur in different branches. However, in QFT, the field represents the particle's state in a single universe. There is no clear framework within QFT to incorporate the existence of multiple universes or branches as suggested by MWI.
Additionally, the interpretation of probabilities in MWI poses challenges in the context of QFT. MWI suggests that probabilities arise due to our subjective uncertainty about which branch or universe we find ourselves in. However, QFT relies on probabilities to describe the outcomes of measurements and interactions within a single universe, without considering multiple branches.
It's important to note that while MWI and QFT are fascinating theoretical frameworks, their combination and compatibility are still subjects of active research and debate. Various attempts have been made to reconcile these frameworks, but a widely accepted and fully consistent framework incorporating both MWI and QFT has not yet emerged.