In the famous two-slit experiment, electrons (or other particles) can exhibit a phenomenon known as wave-particle duality. This means that particles such as electrons can exhibit both wave-like and particle-like behaviors, depending on how they are observed or measured.
When an electron is not observed or measured, it can be described by a wavefunction, which represents the probability distribution of finding the electron at different locations. The wavefunction exhibits wave-like properties, including interference and superposition. In the two-slit experiment, the wavefunction of the electron can interfere with itself, leading to an interference pattern on a screen placed behind the slits.
The statement that the electron is in both slits at the same time does not mean that the electron is physically present in both slits simultaneously, as that would violate our everyday experience and classical intuition. Instead, it reflects the fact that the electron's wavefunction can be described as a superposition of different possible states, including the possibility of passing through either slit.
When the electron is detected or measured, it interacts with the measurement apparatus and collapses into a specific state corresponding to the observed outcome. This collapse is often referred to as wavefunction collapse or measurement, and it selects a particular outcome from the range of possibilities represented by the superposition.
It is important to note that the wave-particle duality and the superposition of states are fundamental features of quantum mechanics. While it might seem counterintuitive based on our macroscopic experience, they have been extensively confirmed by experimental observations in the microscopic realm. The two-slit experiment, in particular, is a powerful demonstration of the wave-particle duality and the interference effects that arise from it.