The 78b number is the radius of the universe, so the diameter is 156 billion light years across.
Was a head scratcher when I first read that. The universe is only 13.7b years old. That is when the big bang took place and the universe was formed. So according to Special Relativity, nothing can travel beyond the speed of light, so really the universe should only have a radius of 13.7b light years and a diameter of 27.4b light years.
I guess it's kind of a technicality that the universe is expanding rapidly, so really nothing has violated special relativity, yet the universe is much bigger than anyone would have really conceived using todays physics.
And yes, the farther away you look, the more "back in time" you are looking. Light only travels so fast. Interesting to think that a star we see in pictures may not even exist anymore.
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