Ask Ethan: How Much Of The Observable Universe Are We Failing To See?
“The Hubble Deep Field saw approx. 13+ Billion Light Years in one direction, so can we can assume we would see 13+ Billion in all directions? The deep field picture showed infant galaxies that are misshapen and just short of the first stars. The big bang itself lies just beyond. Does this imply that the entire universe is roughly 26+ Billion Light Years across? How is it that I have seen estimates showing we only see a small percentage of all the structure that is out there in our universe?”
When we look out at the distant Universe with our most powerful telescopes, as far as we can possibly see, what do we find? Galaxies, smaller and fainter and more and more distant, as far as we’re capable of looking. We have yet to hit the limit of where the galaxies come to an end; as far as we’ve ever been able to look, we’ve found light. Yet at some point, they must cease. There can’t be an infinite number of galaxies in a finite volume of space, and since the Universe has only had 13.8 billion years since the Big Bang, there has to be a finite number of galaxies, and a point beyond which they no longer exist. The deepest view of the Universe, the Hubble eXtreme Deep Field, revealed 5,500 galaxies in a volume comprising just 1/32,000,000th of the sky. But even that appears to be less than 10% of the galaxies out there in the Universe, despite containing galaxies much more distant than 13.8 billion light years.