It is truly amazing to consider that the vast majority of the universe - over 95% - consists of objects and forces that we do not really understand. Despite the fact that atoms make up all observable stars, planets, and objects in the universe, these atoms only make up 4.6% of all of the universe's total density. Most of the universe's density consists of dark energy, a relatively unknown force that is believed to be the cause of the expansion of the universe. Additionally, nearly a quarter of the universe is made up of dark matter, a form of matter we cannot observe visibly.