system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Dark Matter

What is it? What's it use? How does it work?
gpt
Physicists studying the movement and structure of galaxies, and the universe in general, have seen evidence of large amounts of unseen mass interacting with galactic structures, and the unseen mass is called "dark matter". What exactly dark matter is still speculation. Whatever it is it seems to only affect gravity and not interact with electromagnetic radiation (light) or carry a charge. Dark matter is something that should be there according to what we know about gravity, but we can't otherwise detect its presence yet, so we have no other way of analyzing what it is.