  Due to quantum fluctuations, spacetime is foamy on small scales. The degree
of foaminess is found to be consistent with holography, a principle prefigured
in the physics of black hole entropy. It has bearing on the ultimate accuracies
of clocks and measurements and the physics of quantum computation. Consistent
with existing archived data on active galactic nuclei from the Hubble Space
Telescope, the application of the holographic spacetime foam model to cosmology
requires the existence of dark energy which, we argue, is composed of an
enormous number of inert "particles" of extremely long wavelength. We suggest
that these "particles" obey infinite statistics in which all representations of
the particle permutation group can occur, and that the nonlocality present in
systems obeying infinite statistics may be related to the nonlocality present
in holographic theories. We also propose to detect spacetime foam by looking
for halos in the images of distant quasars, and argue that it does not modify
the GZK cutoff in the ultra-high energy cosmic ray spectrum and its
contributions to time-of-flight differences of high energy gamma rays from
distant GRB are too small to be detectable.
