According to quantum mechanics, the behavior of quantum particles can indeed appear different when they are not being observed or measured. This concept is often referred to as the "observer effect" or the "measurement problem."
In quantum mechanics, particles are described by wave functions, which represent the probabilities of various outcomes when measured. The act of measurement causes the wave function to "collapse" into a specific state corresponding to the measurement outcome. This collapse is often considered to be a fundamental and inherent property of quantum systems.
When a quantum particle is not being observed or measured, it is described by its wave function, which evolves according to the laws of quantum mechanics. The wave function evolves in a superposition, where the particle can exist in multiple states simultaneously. This superposition allows for phenomena like interference, where the probabilities of different outcomes interfere with each other.
However, when an observation or measurement is made on the particle, the wave function collapses into a definite state, corresponding to the measurement outcome. This collapse appears to be random and probabilistic. The act of measurement disturbs the superposition and "forces" the particle to take on a specific value for the observed property.
This behavior can lead to the perception that quantum particles behave differently when not being observed. They can exhibit wave-like properties, such as interference and superposition, when not measured, but appear particle-like with definite properties when measured.
It's worth mentioning that there are different interpretations of quantum mechanics, and the exact nature and implications of the observer effect are still the subject of debate and ongoing research in the field of quantum physics.