It is my understanding that the universe is expanding and that matter takes up space. While the universe only contains small percent of matter, wouldn't expansion indicate that the universe is encroaching/growing into other space(other universes, dark matter, dark energy, something)?
What is the universe expanding into (or don't we know)? Or is there some other way of understanding the expanding universe?
Related question about universe itself, not outside of it (unless I misread/misunderstood it)