system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How matter seems so solid when atoms are made of 99.9% empty space.
gpt
So, imagine a magnet. Like a regular old desk magnet with a north and south pole.  Now, take the south pole of that magnet and bring it closer and closer to the south pole of another desk magnet.  

As you know, they're going to resist each other, and you'll feel that resistance well before the magnets actually "touch"---when the only thing between the two magnets (as far as this repulsion effect is concerned) is "empty space."

That's the exact same thing (basically) that's happening with atoms.  They repel because of the ~~magnetic~~ electrostatic properties of the outside of the atoms, and they seem solid because all the matter we would try to push through them repels off of it based on the strength of that repulsion, not based on "touching."