  Gamma-ray bursts (GRBs) are tremendous explosions visible across most of the
Universe, certainly out to redshifts of z=4.5 and likely out to z~10. Recently,
GRBs have been found to have a roughly constant explosive energy as well as to
have two luminosity indicators (the spectral lag time and the variability) that
can be used to derive the burst's luminosity distance from the gamma-ray light
curve alone. There currently exists enough information to calibrate luminosity
distances and independent redshifts for nine bursts. From these, a GRB Hubble
diagram can be constructed, where the observed shape of the curve provides a
record of the expansion history of our Universe. The current nine burst diagram
is sparse, yet formal limits can be placed on the mass density of a flat
Universe. This first GRB Hubble diagram provides a proof of concept for a new
technique in cosmology at very high redshifts. With the launch of the SWIFT
satellite in 2003, we should get ~120 bursts to produce a Hubble diagram
impervious to all effects of dust extinction and out to redshifts impossible to
reach by any other method.
