I'm well aware of the common adage and quantum fact that, until a particle is measured by some sort of instrument, it exists in a state of superposition, can interfere with itself, etc. My questions pertains to the definition of "measurement". In order for something to qualify as a measurement and collapse the wave function, does a human being actually have to observe the results? For instance, let's say you had a Mach–Zehnder interferometer at your disposal, and placed detectors along the photon trajectories that told you down which path the photon traveled. Abiding by the Mach–Zehnder thought experiment, this would collapse the wave function, and you'd have 50-50 odds of seeing the photon at either detector at the end of the experiment. However, what if nobody actually looked at the results? What if the devices made the measurement, but - say - the monitor displaying the results was turned off? The experimenter had no knowledge of what either sensor had actually measured. Will such measurement still collapse the wave function, or will the photons continue on, as though nothing ever happened, and interfere with each other as they would had no measurement taken place? Or will the detectors somehow be included in an even larger wave function, altering the results but not into the 50-50 odds we see when someone makes a direct observation?