> And dark matter is just matter from other universes.

This is a fun idea. You can illustrate it by drawing your classic 2D universe on a piece of paper, sprinkle metal dust around, and move it with magnets held above or below the paper. To the 2D creature, matter in their universe seems to be affected by forces from entirely invisible objects, but 3D creatures can observe exactly what's happening. Likewise our "dark matter" would simply be matter on different planes in the same >3D universe as us. We neither see it nor collide with it, but we observe its gravitational pull.