  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.
