The concept of measurement plays both a central and a problematic role in quantum mechanics. First of all, and unusually, the word ‘measurement’ figures in the fundamental axioms of quantum mechanics - in principle (3) of Chapter 2 for example - and in this quantum physics is quite unlike classical physics as a whole. For though a measurement made on a classical system naturally involves an interaction between the system and a measuring apparatus, there is nothing special according to classical physics about measurement interactions. Describing the measuring process is a straightforward problem of applied classical physics. The classical laws of motion do not break down during the measuring process. For example, suppose you observe a classical particle using light bounced off it. In the classical account you can make the disturbance on the observed system as small as you like and, ‘in principle', you can observe the system with arbitrary accuracy. ‘In principle’ - a favorite expression of the philosopher of physics - means what it always means in physics. The contrast is with ‘in practice'. Of course, in practice there are all sorts of limitations on measurement. There are also some theoretical limitations, like those due to thermodynamics. But these are not the limitations imposed by the theory we are considering, namely classical mechanics. Such limitations as there are are imposed by some other theory. (The expression ‘in principle’ tends to be used when we are discussing the principles of a particular theory and, theoretically but not in practice, physics is a collection of disjoint theories.)
Abstract In the context of the century-long debate on quantum measurement problem, the current work proposes a model that describes the process of collapse of state by quantum interaction, which resolves the controversies of the framework of quantum mechanics and describes the entire domain of quantum-to-classical world including the weak measurement and partial collapse. ‘Measurement’, being the process of physically interacting with a system in order to extracting information from it, is theorized in the current model by synthesizing the quantum interaction between system and measuring apparatus with the information entropy of such process. The model assumes Schrödinger equation to be the only guiding equation for all physical systems including the measuring apparatus, and does not presuppose ‘superposition principle’, rather derives it theoretically from the formulation. The superposed state is shown to be independent of the choice of measurement operator (observable) or basis states (pointers) of the measuring apparatus. Most interestingly, the current model explains the non-observance of ‘superposition principle’ by classical systems as the classical limit of such quantum description of measurement. Along with solving the quantum measurement problem, the work also explains weak measurement and partial collapse, which can be further extended to investigate such several emerging critical phenomena.
Abstract In the context of the century-long debate on quantum measurement problem, the current work proposes a model that describes the process of collapse of state by quantum interaction, which resolves the controversies of the framework of quantum mechanics and describes the entire domain of quantum-to-classical world including the weak measurement and partial collapse. ‘Measurement’, being the process of physically interacting with a system in order to extracting information from it, is theorized in the current model by synthesizing the quantum interaction between system and measuring apparatus with the information entropy of such process. The model assumes Schrödinger equation to be the only guiding equation for all physical systems including the measuring apparatus, and does not presuppose ‘superposition principle’, rather derives it theoretically from the formulation. The superposed state is shown to be independent of the choice of measurement operator (observable) or basis states (pointers) of the measuring apparatus. Most interestingly, the current model explains the non-observance of ‘superposition principle’ by classical systems as the classical limit of such quantum description of measurement. Along with solving the quantum measurement problem, the work also explains weak measurement and partial collapse, which can be further extended to investigate such several emerging critical phenomena.