The observer effect is a principle of physics and states that any interaction between a particle and a measuring device will inevitably change the state of the particle. This is because the act of measurement itself imposes a disturbance on the particle’s wave function, which is the mathematical description of its state.
The concept of observation refers to the act of engaging with an electron or other particle, achieved through measuring its position or momentum.
In the context of quantum mechanics, observation isn’t a passive undertaking, observation actively alters a particle’s state.
This means that any kind of interaction with an atom, or with one of its constituent particles, that provides insight into its state results in a change to that state. The act of observation is always intrusive and will always change the state of the object being observed.
It can be challenging to reconcile this with our daily experience, where we believe we can observe things without inducing any change in them.