system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Before our Sun was a star, before the Solar System was a spinning disk of stuff, where did that stuff come from, and in the empty vastness of space how did those bits of stuff find each other?
gpt
For whatever reason, our universe as we know it began with a very dense collection of energy. So dense and high-energy that matter as we know it could not exist.

It quickly expanded and cooled, and the first matter formed, though exactly what happened at this stage is not totally clear.

Given time, once the expansion had slowed enough, this matter was able to combine and form atoms. Hydrogen, really.

More time, less expansion, and this hydrogen begins clumping together due to gravity. As more and more hydrogen amasses, stars begin to form, where the hydrogen balls are so huge that their own gravity forces the hydrogen atoms at the center to fuse. This process forms heavier and heavier elements as more fusion takes place. Elements up to iron are produced. These are generation one stars.

Eventually, these stars die out. They run out of fuel and, oddly enough, explode, resulting in the creation of heavier matter. Everything above iron.

Then, this exploded material scattered across space comes together to form new stars and planets. Our solar system was formed in this way.