The deeper we peer through the cosmos, the more we are looking into the distant past.  Light from other galaxies takes millions of years to reach us, and so when that light has finally arrived at Earth, it is millions of years old, a snapshot in time of the distant galaxy.  The furthest we can see is so far back in the history of the universe, that galaxies haven’t even formed yet.  As we look at the large-scale structure of the Universe, we see it filled with a cosmic web of galaxy clusters, containing tens of thousands of galaxies each....