We will never know everything and may not be able to see far enough to know much about the outer universe except what it was like billions of years ago. The light from most stars in distant galaxies come from stars that don’t even exist anymore.
Light from the most distant observed object emanated about 13 billion years ago. But that galaxy, if it still exists, would be about 45 billion light years away right now. There are parts of the universe far enough away that they are moving away faster than light travels. Light from those parts will never reach us.