The question you've asked is related to the philosophical concept known as "phenomenalism" or the "problem of existence." Phenomenalism suggests that the existence of something depends on its being observed or perceived. According to this view, objects or events have no intrinsic existence apart from our perception of them.
However, it is important to note that phenomenalism is just one perspective among various philosophical positions on the nature of existence and reality. Other perspectives, such as realism, posit that objects and events have an independent existence regardless of whether they are observed or perceived.
In the realm of science, the concept of observation also varies depending on the context. In quantum mechanics, for example, the act of observing or measuring a particle can influence its behavior, leading to phenomena like wave-particle duality and the observer effect. These observations in quantum mechanics raise intriguing questions about the nature of reality and the role of observation.
Ultimately, the question of whether something exists if it is not observed is a complex philosophical and scientific matter, and different interpretations and viewpoints exist. It's an ongoing topic of debate and exploration in various fields of study.