According to the Copenhagen interpretation of quantum mechanics, which is one of the commonly used interpretations, objects do not physically disappear when we are not observing them. However, the interpretation does suggest that the behavior and properties of quantum systems are fundamentally probabilistic until they are measured or observed.
In the Copenhagen interpretation, a quantum system is described by a wave function, which is a mathematical description that contains all the possible outcomes of a measurement. When a measurement is made, the wave function "collapses" to a specific outcome, and we obtain a definite result. This collapse is often referred to as the "observer effect."
However, it's important to note that the Copenhagen interpretation does not imply that an object ceases to exist or physically disappears when it is not observed. Instead, it suggests that the object's properties are in a superposition of possibilities until a measurement is made, and the act of measurement determines a specific outcome.
The idea of observation or measurement affecting the behavior of quantum systems is a subject of ongoing debate and exploration within the field of quantum mechanics. Other interpretations, such as the many-worlds interpretation or the pilot-wave theory, offer different explanations for the behavior of quantum systems. Each interpretation has its own way of addressing the concept of observation and the nature of reality in the quantum realm.