The problem with universe is that no one knows what really happened.
Everything is based on mathematics calculation and theory which is not always correct.
To Explain how fast universe is expanding, we need to find out how it started. The widely accepted theory of start of universe is the Einsteins theory of relativity, which calculates the start of universe ad Big Bang aka singularity. But the problem with general relativity is that it explains what happened right after the Big Bang but fails to explain what happened at or before the Big Bang. So all laws of physics breaks at singularity.
It is believed, there is Big Bang and Big Crunch in the life cycle of universe. General relativity suggests that at some point, universe starts to shrink and ultimately become so dense that it collapse on itself. And becomes singularity again followed by big bang. So on current theory universe doesn't always expand.

There is new theory published few weeks back that totally rejects the concept of singularity and big bang. But predicts that the universe is there infinitely. There is no start and end.

And the concept of expanding universe is mathematically wrong. Its like saying 1= 2 = 3 ... = infinite. How can new space be created?