Hiding the cosmological constant
  Perhaps standard effective field theory arguments are right, and vacuum
fluctuations really do generate a huge cosmological constant. I show that if
one does not assume homogeneity and an arrow of time at the Planck scale, a
very large class of general relativistic initial data exhibit expansions,
shears, and curvatures that are enormous at small scales, but quickly average
to zero macroscopically. Subsequent evolution is more complex, but I argue that
quantum fluctuations may preserve these properties. 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 nearly invisible at
observable scales.
