  Bursts of weakly interacting particles such as neutrinos or even more weakly
interacting particles such as wimps and gravitons from the very early universe
would offer a much deeper ``look back time'' to early epochs than is possible
with photons.
  We consider some of the issues related to the existence of such bursts and
their detectability. Characterizing the burst rate by a probability $\cal P$
per Hubble four-volume we find, for events in the radiation-dominated era, that
the natural unit of description is the present intensity of the CMB times $\cal
P$. The existence of such bursts would make the observation of phenomena
associated with very early times in cosmology at least conceptually possible.
One might even hope to probe the transplanckian epoch if complexes more weakly
interacting than the graviton can exist. Other conceivable applications include
the potential detectability of the formation of "pocket" universes'' in a
multiverse.
