Abstract: In quantum mechanics, the state of a system is described by the wave function. It is remarkable that, according to the quantum theory, the wave function changes with time in two seemingly distinct ways. There is a change in time that can be calculated from the time-dependent Schrodinger equation, and also the wave function is believed to change discontinuously as a result of measurements. However, despite much effort, what constitutes a measurement and how a measurement causes a change in the wave function remains unclear. I will describe a series of experiments in which a part of the wave function of an electron is trapped in a box with walls sufficiently thick to prevent escape by tunneling.