The universe is full of mind-bending facts that are just a little tough to believe. At the top of that list is the fact that atoms are nearly all empty space (99.999999999%). What's that mean for us as humans? All the matter that makes up the human race could fit in a single sugar cube.
But doesn't that mean that because of that empty space, we could potentially walk through solid objects without colliding? Unfortunately not. When two atoms try to pass through each other, the electronic shells repel each other like two negatively charged particles. Essentially, everything that contains atoms has a strong negatively charged shell around it, repelling and preventing them from passing right through one another.
Only about four percent of the Universe's mass makes up everything (people, objects, planets, etc). The rest is made up of dark matter and dark energy, completely invisible to the naked eye. This stuff fills all the empty space and repulses gravity.
You may be thinking you've seen it all, but it turns out you can't see the vast majority of mass.
