  We propose possible properties of quantum gravity in de Sitter space, and
find that they relate the value of the cosmological constant to parameters of
the Standard Model. In de Sitter space we suggest (i) that the most sharply
defined observables are obtained by scattering objects from the horizon and
back to the horizon and (ii) that black holes of discrete charge are well
defined states in the theory. For a black hole of minimal discrete electric
charge, we therefore demand that a scattering process involving the black hole
and a probe can take place within a Hubble time before evaporating away, so
that the state of a discretely charged black hole is well defined. By imposing
that the black hole's charge is in principle detectable, which involves
appreciably altering the state of a scattered electron, we derive a relation
between the Hubble scale, or cosmological constant, and the electron's mass and
charge and order one coefficients that describe our ignorance of the full
microscopic theory. This gives the prediction $\Lambda \sim 10^{-123 \pm 2}
M_{Pl}^4$, which includes the observed value of dark energy. We suggest
possible ways to test this proposal.
