  We propose a phenomenological approach to the cosmological constant problem
based on generally covariant non-local and acausal modifications of
four-dimensional gravity at enormous distances. The effective Newton constant
becomes very small at large length scales, so that sources with immense
wavelengths and periods -- such as the vacuum energy-- produce minuscule
curvature. Conventional astrophysics, cosmology and standard inflationary
scenaria are unaffected, as they involve shorter length scales. A new
possibility emerges that inflation may ``self-terminate'' naturally by its own
action of stretching wavelengths to enormous sizes. In a simple limit our
proposal leads to a modification of Einstein's equation by a single additional
term proportional to the average space-time curvature of the Universe. It may
also have a qualitative connection with the dS/CFT conjecture.
