User:Authorfieldsofcolor/sandbox/measurement problem

A completely different and much simpler solution is offered by Quantum Field Theory. The measurement problem arises because Quantum Mechanics does not offer a picture of reality at every instant. Instead it describes superpositions of states with various probabilities until someone looks. On the other hand, Quantum Field Theory, in its “fields only” sense as formulated by Julian Schwinger,* does offer such a picture, namely fields (properties of space) and field intensities that are present at every point. However the field intensities are specified by vectors in an abstract Hilbert space, not by simple numbers. These fields evolve as specified by the QFT equations, but the equations do not tell the whole story. They do not describe how energy is transferred from one quantum to another. So in addition to the deterministic evolution governed by the equations, there is another process in which a field quantum deposits its energy (or part of its energy) into another quantum and disappears from all other points in space. While this process is not covered by the equations of QFT, it is necessary if quanta are to act as indivisible units.** Thus the QFT picture of a measurement consists of two phases. In the first phase an incident quantum, say a radiated photon, interacts with all quanta that it encounters, as per the field equations. This interaction is reversible and may be called the “entanglement” phase (although that word is sometimes used in other senses). Then, at some point that cannot be determined by the theory, the incident quantum collapses into one of these other quanta, say an atom in a Geiger counter, and transfers its energy to it. This initiates a chain of events that may lead to a macroscopic change, e.g., the death of a cat. While QFT does not specify when this collapse happens, it states that nothing happens until the quantum collapses, and after that everything is inevitable. In fact the QFT picture is the same as the “classical” picture: When the radiated quantum collapses into the Geiger counter, it creates an electric current that trips a relay that releases the poison gas that kills the cat. What could be simpler?
 * Julian Schwinger “The Theory of Quantized Fields” a series of five papers in Phys. Rev. 1951-54