  The determination of the densities of intergalactic photons from the FIR to
the UV produced by stellar emission and dust reradiation at various redshifts
can provide an independent measure of the star formation history of the
universe. High energy gamma-rays can annihilate with FIR-UV photons to produce
electron-positron pairs which result in high-end absorption cutoffs in the
gamma-ray spectra of extragalactic sources. Future measurements of such
absorption in the spectra of extragalactic high energy gamma-ray sources at
higher redshifts from detectors such as the (soon to be launched) GLAST space
telescope can be used to determine intergalactic photon densities in the
distant past, thereby shedding light on the history of star formation and
galaxy evolution. (abridged),
