The universe is teeming with very high energy gamma ray sources (> 100 GeV), but it is generally thought that their impact on the universe is minor at best. On energetic grounds, this assumption seems well-founded because the energy density in TeV photons is 0.2% of that of ionizing photons from quasars. However, as I hope to show in this talk, this is not the case. Rather, the greater efficiency by which TeV photons can be converted to heating in the intergalactic medium (IGM) allows TeV blazars dominate the heating of the IGM at low redshift. I will discuss the nature of this conversion via beam instabilities. I will then discuss how the resultant heating from these TeV sources makes dramatic differences in the formation of structure in the universe. In particular, I will discuss how it gives rise to the inverted temperature-density profile of the IGM, the bimodality of galaxy clusters, and the paucity of dwarf galaxies in galactic halos and voids.
Followed by wine and cheese in Pupin 1402.