system
Given the following post, respond as if you're commenting on Reddit:
human
If the universe was formed in a single event, why isn't it homogeneous? As in, why do stars and planets have vastly different compositions if they originated from the same point?
gpt
The leading theory is that during the period of cosmic inflation, in which the universe expanded much faster than the speed of light, quantum mechanical fluctuations were collapsed and then magnified as they expanded, which lead to the fluctuations that caused galaxies and the like.

Planets and stars have different compositions because they did not originate from the same point. The first generation of stars would have all had the same composition, but once they fused heavier elements (up to iron and heavier in big star collapses) and then supernova'd them into the universe, new stars formed from their remains and so have different compositions.