When people say that electrons don't "exist" before observation or interaction, they are referring to a concept in quantum mechanics known as wave function collapse or the measurement problem.
In quantum mechanics, particles such as electrons are described by wave functions, which represent the probabilities of finding the particles in different states or locations. These wave functions can be thought of as a superposition of all possible states that the particle could occupy.
However, when a measurement or observation is made on a quantum system, the wave function "collapses" into a specific state corresponding to the observed outcome. This collapse is a probabilistic process, and the outcome of the measurement is one of the possible states determined by the probabilities in the wave function.
The statement that electrons don't exist before observation or interaction is a way of highlighting the peculiar nature of quantum mechanics. Until a measurement is made, the electron is described by a superposition of states, meaning it is not in a definite position or state but rather exists in a combination of possibilities. It's only upon measurement that one of those possibilities is realized and the electron is observed in a particular state.
This behavior challenges our classical intuition, where objects are expected to have definite properties independent of observation. In the quantum realm, however, the act of measurement plays a crucial role in determining the observed outcome and collapses the wave function into a specific state.
It's important to note that this statement should not be taken to mean that the electron doesn't exist at all or that it is created by observation. Rather, it reflects the unique nature of quantum mechanics, where the behavior of particles is inherently probabilistic and can only be described by wave functions until a measurement occurs.