Astronomers believe the whole known universe is moving away from us because of the continual outward expansion that they are observing. This is known as Hubble's Law. A way that I was told that is easily explainable is to think about baking raisin bread. As the bread bakes, the raisins will continue to move away from each other even though they are still in the bread dough. The raisins being the galaxies and the dough being the expanding universe. I hope this helps :)
