If all measuring scales shrink No one will know and We'll all assume everything else got bigger. amirite?

No, there would be proof that everything didnt get bigger. I dont feel like googling it but it has to do with mass tripling if evrything doubled in size

Well yes, but no. A meter is defined by the speed of light. If it changes, much else has to change, which means… probably the universe collapses or smth, dunno.