it means there is a factor of -1 missing. Generally, the wave function for the lowest state coming down is still ok. The probability is given by the square of the wave function, so wave function pointing up or down would give same probability.

it means there is a factor of -1 missing. Generally, the wave function for the lowest state coming down is still ok. The probability is given by the square of the wave function, so wave function pointing up or down would give same probability.