Time as self-adjoint operator?

[arivero]

It has been asked if there exists an operator representing time. I remember some negative answers, but I do not remember the arguments.

In relativistic QM this relates to the non-existence of position operators; we are working with an (t,x,1,x2,x3) vector there. Also I believe to remember some provlem with velocity operators -its eigenvectors been only +c and -c, or so- but I am unsure about if both questions are related.

also, Energy-time indetermination is usedto estimate decay rates of particles. But there an operator is not invoked.

[damgo]

See http://math.ucr.edu/home/baez/uncertainty.html

There is a discussion of the time/energy UP, and a sketch of why there can be no true time operator.