system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do theoretical physicists find solutions to the biggest and smallest answers to the universe using math alone?
gpt
They don't.

They have centuries of observations to draw upon, they are trying to find math that is consistent with those observations.  Sometimes that math takes them beyond what can be shown with experiments, but by no means are they using math alone.