What if there's a billion year cycle of slight expansion and slight contraction? How could we ever notice that when we're in the expansion phase of the cycle?
The expansion of the universe was decelerating several billion years ago, then it began to accelerate again. The Standard Model accounts for this as being caused by gravity--the expansion was decelerating because of the force of gravity pulling everything together. It finally hit a "breaking point" where the expansion was no longer hampered by gravity, which allowed it to begin accelerating once more.