  Quantum physics, despite its observables being intrinsically of a
probabilistic nature, does not have a quantum entropy assigned to them. We
propose a quantum entropy that quantify the randomness of a pure quantum state
via a conjugate pair of observables forming the quantum phase space. The
entropy is dimensionless, it is a relativistic scalar, it is invariant under
coordinate transformation of position and momentum that maintain conjugate
properties, and under CPT transformations; and its minimum is positive due to
the uncertainty principle. We expand the entropy to also include mixed states
and show that the proposed entropy is always larger than von Neumann's entropy.
We conjecture an entropy law whereby that entropy of a closed system never
decreases, implying a time arrow for particles physics.
