THE EVOLUTION OF GALAXY NUMBER DENSITY AT z107 Me. By using the M*=106 Me lower limit we further show that the total number of galaxies in the +0.7 12 universe up to z=8 is 2.00.6 ´ 10 (2 trillion), almost a factor of 10 higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox. Key words: galaxies: evolution – galaxies: fundamental parameters – galaxies: general – galaxies: high-redshift – galaxies: luminosity function, mass function – galaxies: structure Djorgovski et al. 1995), and reached our current depths after deep Hubble Space Telescope (HST) imaging campaigns were carried out, especially within the Hubble Deep Field (Williams et al. 1996). This was later expanded to other deep fields such as the Hubble Deep Field South (Williams et al. 2000), the Great Observatories Origins Survey (Giavalisco et al. 2004), and the near-infrared CANDELS fields (Grogin et al. 2011; Koekemoer et al. 2011), and finally to the Hubble Ultra-Deep Field (HUDF; Beckwith et al. 2006), which remains the deepest image in the optical and near-infrared of our universe taken to date. However, despite these surveys it is still uncertain how the total number density of galaxies evolves over time. This is an interesting question as we know that the star formation rate rises, and then declines at z
