system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if atoms are almost completely empty space and I am made up of atoms, then what is stopping me from walking through walls if the empty space lines up right?
gpt
Electromagnetism! The electrons in the atoms of your butt repel the electrons in the atoms of the chair beneath you, so you don't fall right through it. 

It's not a question of "if the empty spaces line up", the empty spaces are almost always "lined up". You cannot fathom how tiny electrons and nuclei are and the vastness of space between them, every picture you've ever seen exaggerates their size. If a proton is a pea, then a hydrogen atom is a football stadium, and the electron is a grain of sand somewhere in that stadium. But the proton and more importantly, the electron have extremely powerful (relative to their size) electric charge.