Hi I rarely have a background in physics (yet!) But based on my popular knowledge I understand that the Universe is 'expanding' in a loose sense of the word - which basically equates to the fact new space is being created all the time which in turn resembles a Universe where the distances between objects appear to grow and grow. The 'Dark Matter' theory however hypothesizes some kind of matter which physicists don't understand and the fact due to some properties of this matter objects appear to be getting pushed away from each other. My question is - why does there need to be this unverified substance 'dark matter'. Why is it never said that new space being created is the reason for the accelerating expansion of the Universe. Why bring Dark Matter into the equation at all?