A causally well-behaved solution of the localization problem for the free
electron is given, with natural space-time transformation properties, in terms
of Dirac's position operator. It is shown that, although this operator does not
represent an observable in the usual sense, and has no positive-energy
(generalized) eigenstates, the associated 4-vector density is observable, and
can be localized arbitrarily precisely about any point in space, at any instant
of time, using only positive-energy states. A suitable spin operator can be
diagonalized at the same time.Comment: 19 pages including 1 figure (1 LatTex2e file, 1 postscript file).
Uses package amssymb. Typos correcte
