If there is enough matter in the universe to stop the expansion associated with the big bang, we say that the universe is closed. In a closed universe, the current period of expansion will be followed by a period of contraction (sometimes called the Big Crunch) as the gravitational force pulls matter back in. Searching for matter to “close” the universe is a major task of modern cosmology. (See also dark matter, flat universe, and open universe.)
Learn more about closed universe