Dark title card reading 'The i Is in the Equation' above two boxed equations: F equals m a in amber with a green tick marked 'Re Psi solves it', and the Schrodinger equation in pink with a cross marked 'Re psi does not'.

The i Is in the Equation

Classical physics uses complex numbers constantly and can always discard them at the end. Quantum physics cannot, and the reason is exact: take the real part of a classical solution and you still have a solution — take the real part of a wavefunction and you have nothing. A lesson for philosophers and theologians on what F = ma actually claims, and what quantum mechanics does and does not license. … readThe i Is in the Equation