  There are enough reasons for us to consider time as a dynamical variable or
operator; but according to Pauli's argument the existence of a self-adjoint
time operator is incompatible with the semi-boundedness of Hamiltonian
spectrum. In this article, we study the expressions of time operator and the
definitions of mean time from a general and new viewpoint, make a new comment
on Pauli's objections, and clarify some possible confusion in existing theories
of time in quantum mechanics. From which we try to provide a new gateway for
the conundrum of time in quantum mechanics and reconstruct a unified foundation
for some issues of time.
