According to the Copenhagen interpretation of quantum mechanics, there is a concept known as "wavefunction collapse" or "quantum measurement," which suggests that the act of observation or measurement can influence the behavior of quantum systems. This interpretation proposes that the wavefunction, which describes the probabilistic nature of a quantum system, undergoes a collapse or reduction to a specific state when measured.
One possible consequence of this interpretation is the idea that a particle's properties, such as its position or momentum, are not well-defined until they are observed. In other words, some interpretations suggest that the particle exists in a superposition of states until an observation or measurement is made, at which point the wavefunction collapses, and the particle assumes a definite state.
However, it's important to note that the Copenhagen interpretation is just one interpretation of quantum mechanics, and there are alternative interpretations, such as the Many-Worlds interpretation and the Pilot-Wave theory, which offer different explanations for the behavior of quantum systems.
Furthermore, outside the realm of quantum mechanics, in macroscopic everyday life, objects do exist independently of our observation. The behavior of macroscopic objects is governed by classical physics, which is deterministic and does not exhibit the same quantum phenomena observed at the microscopic level.
Ultimately, the question of whether objects exist only when observed is still a topic of debate and interpretation within the field of quantum mechanics, and different interpretations provide different perspectives on this matter.