In a 1942 paper, Dirac claimed that negative energy and negative this quantity are not nonsense and are mathematically well-defined like negative money. For a spin-0 particle, the current of this quantity is equal to (15[1])(read slowly) h-bar over 2-m-i times (15[1])psi-star-del-psi minus psi-del-psi-star. Application of the WKB approximation to a free particle (*) wavefunction gives a nonzero value to this quantity in classically forbidden regions. Born’s rule set the square norm of the wavefunction amplitude as this quantity. QBism is an interpretation of Quantum Mechanics which uses a subjective Bayesian account of this quantity. This quantity over all space for a normalized wavefunction is equal to one. For 10 points, identify this quantity that gives the chance of observing a particle in a particular state. ■END■