We present a new solution to the cosmological constant ( CC ) and coincidence problems in which the observed value of the CC , \Lambda , is linked to other observable properties of the universe .
This is achieved by promoting the CC from a parameter which must to specified , to a field which can take many possible values .
The observed value of \Lambda \approx ( 9.3 { Gyrs } ) ^ { -2 } ( \approx 10 ^ { -120 } in Planck units ) is determined by a new constraint equation which follows from the application of a causally restricted variation principle .
When applied to our visible universe , the model makes a testable prediction for the dimensionless spatial curvature of \Omega _ { k 0 } = -0.0056 ( \zeta _ { b } / 0.5 ) ; where \zeta _ { b } \sim 1 / 2 is a QCD parameter .
Requiring that a classical history exist , our model determines the probability of observing a given \Lambda .
The observed CC value , which we successfully predict , is typical within our model even before the effects of anthropic selection are included .
When anthropic selection effects are accounted for , we find that the observed coincidence between t _ { \Lambda } = \Lambda ^ { -1 / 2 } and the age of the universe , t _ { U } , is a typical occurrence in our model .
In contrast to multiverse explanations of the CC problems , our solution is independent of the choice of a prior weighting of different \Lambda -values and does not rely on anthropic selection effects .
Our model includes no unnatural small parameters and does not require the introduction of new dynamical scalar fields or modifications to general relativity , and it can be tested by astronomical observations in the near future .