Negative Observations in Quantum Mechanics

In quantum mechanics, it is possible to make observations that affect physical entities without there being a physical interaction between the observer and the physical entity measured. Epstein (1945) and Renninger (1960) discussed this situation, and Renninger called this type of observation a "negative observation." Empirical research on electron shelving supports the possibility of negative observations (Bergquist, Hulet, Itano, and Wineland, 1986; Nagourney, Sandberg, and Dehmelt, 1986; Sauter, Neuhauser, Blatt, and Toschek, 1986). Two scenarios are presented that emphasize the role of human observation in negative observations. The first is modeled after the two hole gedankenexperiments of Feynman, Leighton, and Sands (1965) and portrays negative observations in a non-technical manner. The second scenario allows for quantifying the affect on physical entities of negative observations in a simple fashion. In addition, various issues related to negative observation are discussed, including an objection that might be raised. The Schrodinger cat gedankenexperiment is discussed briefly as well.