A great visualization, is to imagine that space remains unchanged, but everything in it is shrinking at the same rate. The shrinking people don't perceive they

A great visualization, is to imagine that space remains unchanged, but everything in it is shrinking at the same rate. The shrinking people don't perceive they are shrinking, or that anything else is shrinking. But the distances between things not held together by significant forces (like chemical or gravitational bonds) appear to be growing and growing. And space isn't expanding >into< anything. It is just relative changes between bond forces and space, creating the experience of more space. There is no impact of this expansion "outside" the universe (that we know of, of course).