  It is pointed out that a collider experiment involves a local contribution to
the energy-momentum tensor, a circumstance which not a common feature of the
current state of the Universe at large characterized by the cosmological
constant $\Lambda_0$. This contribution may be viewed as a change in the
structure of space-time from its large scale form governed by $\Lambda_0$ to
one governed by a $\Lambda$ peculiar to the scale of the experiment. Possible
consequences of this effect are explored by exploiting the asymptotic symmetry
of space-time for non-vanishing $\Lambda$ and its relation to vacuum energy.
