PEMDAS origins.

I asked a question in r/AskReddit about this and the general response was that PEMDAS was created to provide a uniform approach. there are posts like 6+6x6+6 where the answer is 48, 78, or 144 depending on the use of PEMDAS. but if PEMDAS was just kind of created to provide structure and order, then how do physicists and scientists use math to predict or prove different phenomena, especially in areas where we can’t replicate the exact physical conditions. seems like an arbitrary thing like PEMDAS would need to have a proven reason to be the rule.