  Einstein's most famous equation -- $E=mc^2$ -- generated a short-circuit
between the concepts of mass and energy, which also affects other concepts like
matter, radiation, and vacuum. Physics currently has a mixture of classical,
relativistic, and quantum concepts of mass, which generates a great deal of
confusion and many problems. Clear definitions need to be established if one
wants to avoid ghost hunting. In particular, by abandoning the idea of mass and
focusing on time and energy, some interesting implications are emerging. It is
noted that the cutoff frequency of the quantum vacuum energy, consistent with
the observations of the cosmological constant, corresponds to that of the
Cosmic Microwave Background. This might be consistent with the hypothesis of a
rotating and expanding universe described by a Kerr-de Sitter metric with the
observed cosmological constant. To verify this hypothesis is crucial to prove
the rotation of the universe.
