Negative Observations in Quantum Mechanics

Abstract

In quantum mechanics, it is possible for a person to make observations that affect physical entities without there being a physical interaction between the human 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 for negative observation are presented in this paper. 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 effect on physical existents 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 Schrödinger cat gedankenexperiment is discussed as well.