  The timelike tube theorem asserts that in quantum field theory without
gravity, the algebra of observables in an open set U is the same as the
corresponding algebra of observables in its ``timelike envelope'' E(U), which
is an open set that is in general larger. The theorem was originally proved in
the 1960's by Borchers and Araki for quantum fields in Minkowski space. Here we
sketch the proof of a version of the theorem for quantum fields in a general
real analytic spacetime. Details have appeared elsewhere.
