Fact could be opinion?

Dont judge this question by the title please allow me some space to elaborate... Fact is nothing but a mojority belief. Sure laws are proven and whatnot, but what is the PROOF based on? At the time when numbers were invented [or the names for numbers were], 2+2=4... BUT if everyone at the time believed 2+2 should equal 5 or 20 or 22 thats the way it would be. Thus altering a vast majority of proven laws because of their opinion... So i believe fact is technically a widespread opinion. This isn't a question entirely just lookin for some educated responses...