This difference is large enough that some scientists speculate that something significant might be missing from our standard model of the universe's evolution.

Oh I’m sure there’s “something” missing. In fact most of something, if the “dark matter” proponents are to be believed.

My theory is that there are trillions of dead galaxies and stars floating around, and with a black hole at the center we simply can’t see them because they’re, well, black. Not just the center: Including all the stars that circle and planets which circle them. They’re dead, you see. In space “dead” = “black”, at least at distance. Unobservable, unmeasurable.

Shortly after the Big Bang as energy accreted into matter it was still close together relatively speaking. Gravitational attraction would have formed stars, then galaxies *much* faster than we are used to today, and that led to billions or trillions of proto-galaxies forming within a few tens or hundreds of millions of years. They also burned out quickly because they were mostly gigantic, massive stars which can burn through their fuel in just a few million years, meaning it would be entirely possible for whole galaxies to have lived and died quickly and which would be unaccounted for (except by indirect gravitational measurements) in our “sighted” (visual, infrared, etc.) observations.

Get enough of those, impossible to see, not emitting any kind of radiation, and you have a huge source of matter which accounts for “the standard model” which is having trouble accounting for all manner of stuff.

Speaking of which, the edge of the universe isn’t really the edge, and our inference of how old the universe is is wrong, too. It’s been around a lot longer, and some things past “the edge” just aren’t measurable because they’re moving too fast, their radiation/energy is beyond our ability to see. But that’s for another post someday.