If a quantum particle is observed to have a definite position, what is the underlying cause according to quantum state dynamics?

When a particle is measured to be at a definite position, the quantum state “collapses” to a position eigenstate, a process driven by the interaction with the measuring apparatus. This collapse is not a physical motion but a mathematical update that removes all other possible positions from the wavefunction. The underlying cause is the entanglement between the particle and the measurement device, which forces the superposition to reduce to a single outcome. For example, when an electron hits a screen, its wavefunction spreads over many points, but the act of detection at one spot instantaneously eliminates the other possibilities. Thus, the definite position results from the measurement‑induced collapse of the quantum state.