  We present an extension of general relativity in which the cosmological
constant becomes dynamical and turns out to be conjugate to the Chern-Simons
invariant of the Ashtekar connection on a spatial slicing. The latter has been
proposed in \cite{Chopin-Lee} as a time variable for quantum gravity: the
Chern-Simons time. In the quantum theory the inverse cosmological constant and
Chern-Simons time will then become conjugate operators. The "Kodama state" gets
a new interpretation as a family of transition functions. These results imply
an uncertainty relation between $\Lambda$ and Chern-Simons time; the
consequences of which will be discussed elsewhere.
