system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is there nothing in space? I get that there isn’t necessarily air like we have in our atmosphere on Earth, but how can there be nothing?
gpt
Most theories think the universe started out as mostly gaseous, but particles of matter attract each other through the force of gravity (which is something you get for free, as a fundamental property of matter). When matter starts to clump together, voids are left in space - and over a very, very long time, those voids get very large.

There are still gas clouds out in space, but there is a lot of volume of space that contains nothing at all.