If it [the universe] was expanding fairly slowly, the force of gravity would cause it eventually to stop expanding and then to start contracting. However, if it was expanding at more than a certain critical rate, gravity would never be strong enough to stop it, and the universe would continue to expand forever.
![If it [the universe] was expanding fairly slowly, the force of gravity Image](https://www.idlehearts.com/images/if-it-the-universe-was-expanding-fairly-slowly-the-force-of-gravity.jpg?x85372 "If it [the universe] was expanding fairly slowly, the force of gravity")
