Can anyone explain to me what how is the act of observation defined in quantum mechanics? It is commonly said that the double slit experiment shows that if one simply observes the state of the electron as it passes through the slits, it effects the results. Many forms of observations are possible, from measurements of small currents induced by the passing of the charged electron, though measurements of the transferred momentum in the interaction with the slit. But are all these kinds of measurements and others considered observations? Would simply plugging off the machine which makes the measurements, cancel the observation? Would a burning of the output also eliminate it? So I guess my question is: What makes an observation an observation?