  I consider novel ways by which Gamma-Ray Bursts (GRBs) and quasars can be
used to probe the universe. Clues about how and when was the intergalactic
medium ionized can be read off the UV emission spectrum of GRB explosions from
the first generation of stars. The existence of intergalactic and galactic
stars can be inferred from their gravitational microlensing effect on GRB
afterglows. Prior to reionization, quasars should be surrounded by a halo of
scattered Lyman-alpha radiation which probes the neutral intergalactic medium
(IGM) around them. The situation is analogous to the appearance of a halo of
scattered light around a street lamp which is embedded in a dense fog. Outflows
from quasars magnetize the IGM at all redshifts. As a result, the shocks
produced by converging flows during the formation of large scale structure in
the IGM, accelerate electrons to relativistic energies and become visible in
the radio regime through their synchrotron emission and in the gamma-ray regime
through their inverse-Compton scattering of the microwave background photons.
During transient episodes of strong mergers, X-ray clusters should therefore
appear as extended radio or gamma-ray sources on the sky.
