system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: By what process did the first electrons, neutrons and protons to form into atoms?
gpt
Different atoms formed through different processes.

The lightest atoms (hydrogen, helium, and lithium) were formed immediately after the big bang in a short window where pressures were still high enough to smash these particles together but high energy light had dispersed enough to not blow them apart.

All elements heavier than lithium but lighter than iron and nickel are formed in the cores of stars.  Pressures and temperatures there are high enough to force light atoms together into heavier ones in a process that releases energy and fuels the star.

Everything heavier than iron and nickel *consume* energy when fused, these atoms only form when massive stars implode under their own weight and briefly crush heavy elements together before destabilizing entirely.