  Discussions are made on the relationship between physical states and gauge
independence in QED. As the first candidate take the LSZ-asymptotic states in a
covariant canonical formalism to investigate gauge independence of the
(Belinfante's) symmetric energy-momentum tensor. It is shown that expectation
values of the energy-momentum tensor in terms of those asymptotic states are
gauge independent to all orders. Second, consider gauge invariant operators of
electron or photon, such as the Dirac's electron or Steinmann's covariant
approach, expecting a gauge invariant result without any restriction. It is,
however, demonstrated that to single out gauge invariant quantities is merely
synonymous to a gauge fixing, resulting again in use of the asymptotic
condition when proving gauge independence. Nevertheless, it is commented that
these invariant approaches is helpful to understand the mechanism of the
LSZ-mapping and furthermore of quark confinement in QCD. As the final
candidate, it is shown that gauge transformations are freely performed under
the functional representation or the path integral expression on account of the
fact that the functional space is equivalent to a collection of infinitely many
inequivalent Fock spaces. The covariant LSZ formalism is shortly reviewed and
the basic facts on the energy-momentum tensor are also illustrated.
