The Origin of the Born Rule from Spacetime Averaging

Abstract: The Born rule postulates that the probability of measurement in quantum mechanics is related to the squared modulus of the wave function $\psi$. We rearrange the equation for energy eigenfunctions to define the energy as the real part of $\hat{E}\psi/\psi$. For an eigenstate, this definition gives a constant energy eigenvalue. For a general wave function, the energy fluctuates in space and time. We consider a particle in a one-dimensional square well potential in a superposition of two states and average the energy over space and time. We show that, for most cases, such an energy expectation value differs by only a few percent from that calculated using the Born rule. This difference is consistent with experimental tests of the expectation value and suggests that the Born rule may be an approximation of spacetime averaging.