Mathematicians just solved a 125-year-old problem, uniting 3 theories in physics

It's interesting how so many important papers are always on arxiv first. it makes me wonder what purpose peer reviews serves. I think also, this is to help establish priority over the result. So getting it up on arxiv is like a timestamp to avoid someone else deriving it at the same time and getting credit by having it published first.

Peer review is important for checking the correctness of the results, among other things. It's not uncommon to find big errors; small mistakes are everywhere.