Expanding Universe: Discussion

We have seen that there is evidence that the Universe is expanding. Consider hitting a tennis ball with a tennis racket. The ball's speed is determined by how fast you hit it. And after you hit the ball, it starts to slow down. It won't accelerate unless you hit it again. But recently, some astronomers have found evidence which suggests that the Universe is accelerating. If this is true, it will require major revisions in our thinking about the how the Universe works.