If that were their 'function' they're failing at it. Because not only is the universe NOT slowing down (due to the combined gravitational effects of objects within it) its expansion rate is actually increasing! At during the course of the past several billion years, so they think, at least at this time. They base this on their direct observations of deep space objects and how fast they seem to be moving away from us, using various speed-measuring techniques.
And what is it expanding into? If I could travel fast enough to reach the edge of the universe and keep going outracing the expansion. Where would I find myself?