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Suppose the universe really does have a huge cosmological constant.
Would we necessarily know? I show that if one does not assume
homogeneity or an arrow of time at the Planck scale, a large class
of initial data for general relativity exhibits expansions and
shears that are enormous at small scales, but quickly average to
zero macroscopically. Subsequent evolution is more complicated,
but I argue that quantum fluctuations should preserve this property. The resulting picture is a version of Wheeler's ``spacetime foam,''
in which the cosmological constant produces high curvature at the
Planck scale but is hidden at observable scales.