According to quantum physics, the behavior of particles at the quantum level is described by wave-particle duality and the principle of superposition. This means that particles can exist in multiple states or locations simultaneously until they are observed or measured. This concept is often referred to as the observer effect.
In quantum mechanics, the act of observation or measurement "collapses" the wavefunction, which is a mathematical description of all the possible states the particle can be in, into a single state. This collapse occurs when the particle interacts with its environment, such as through measurement or interaction with other particles.
However, it is important to note that this observer effect does not mean that the particle ceases to exist or that it only exists when observed. Rather, it suggests that the properties of a particle, such as its position or momentum, become well-defined and definite upon measurement.
Outside of the quantum realm, in the macroscopic world we interact with every day, classical physics accurately describes the behavior of objects. Classical physics does not exhibit the same kind of wave-particle duality or observer effect as observed in quantum mechanics.
Therefore, while the behavior of particles at the quantum level can be influenced by observation or measurement, it does not mean that things only exist when observed or cease to exist when unobserved in the everyday sense.