In order to understand the relationship between the wave function ψ and the particles it describes, we can observe an electron diffraction experiment.

If the intensity of the electron flow is very small, even if it is emitted one by one, only diffraction spots can be displayed on the screen, which fully shows the particle size. At the beginning, these diffraction spots are chaotic, and with the extension of time, the diffraction spots gradually increase, showing regularity, and the final image is still a diffraction ring with alternating light and dark, thus showing volatility.

It can be seen that the fluctuation of electrons is the statistical result of the motion of many independent particles under exactly the same conditions, so the wave function ψ is also a description of the statistical law of particle motion.

ψ is a wave function, which is a mathematical function in quantum mechanics to describe the motion state of electrons outside the nucleus, that is, a wave function represents a motion state of electrons, which is called atomic orbit for historical reasons.

The meaning of wave function ψ has the following three aspects:

(1) wave function ψ is a mathematical function that describes the motion state of electrons outside the nucleus.

(2) Each wave function ψ has corresponding energy e .. The same energy state in the same atom constitutes an energy level layer.

(3) The square ψ2 of the wave function is the probability density, which indicates the probability that an electron appears in a unit volume near a certain point in space at time t. ..

So the concepts such as the orbit of particles in classical physics disappeared, replaced by the probability of finding particles in the space outside the core. This is one of the essential differences between quantum mechanics and classical Newtonian mechanics.