We learned long ago that an atom was comprised mostly of nothing. Inside the electron shell there is a vast area of nothing until you get to the nucleus where you'll find the Neutrons and Protons. The amount of stuff in there is almost negligible in size but significant in it's force since it's this stuff that makes it what it is.
In order for much of modern cosmological theories to work theorists have postulated the existence of Dark Matter. It is another type of matter than the stuff that we can see and from which we're all made. It doesn't react with our regular baryonic type of matter so we can't observe it directly but is thought to comprise the vast majority of the mass off the matter of the Universe anyway, about fifty times more Dark Matter than regular matter.
But wait, that's not all. As much Dark Matter as there is, it's only about a third of the theorized amount of Dark Energy. Even though it is just energy and not matter, there is so much of this Dark Energy that it nevertheless makes up about three quarters of the mass of the Universe.
According to these theories the stuff of planets, stars and galaxies only comprise about less than one half of one percent of the stuff of existence. We're more special than you might think.