The relativity of energy and frequencies

A relativity theory in the space of energy and frequenciesis developed and a Lorentz-like transformation between these variables, in which Planck's constant h takes the role of the traditional 1/c (where c is the speed of light), is derived. We use the constancy of the intrinsic angular momentum of the photon, as expressed by the invariance of the line element E ² -h ² f ², instead of the constancy of the speed of light as manifested by the invariance of the line element c ² t ²-x ². The transformation is then expressed in terms of the red-shift parameter z and applied to the particular cases in which the frequency is varied due to the velocity, to gravitational energy, and to motion in a central Coulomb field.