Expanding is not the term to use in this question, in my view.  If you ask me if the universe is expanding, then I would have to say, not only yes, but, into what, the universe was expanding.  I don’t think that there is scientific proof of any kind that the universe is expanding INTO ANYTHING.  We would have to be outside of the universe to be able to perceive such a change; and, of course, we cannot get outside of our own universe.   What scientists do know is this, the galaxies that we study right now, are in fixed patterns in our universe.  They are stationery and do not move around.   The space between the galaxies is stretching or seems to be moving away, as time passes.  If you view the universe in this way and ask “is the universe stretching”, the answer would be YES.