Actually, they AREN’T cut to that degree of accuracy, the only “expert” who claims they are was the asshole on ancient aliens who used a carpenters square on it (which, as a carpenter, I can tell you those things are a far cry from laser precise) and even with THAT he said they where “accurate-ish” hiding the fact that while being recorded his own tools proved they where not in fact perfect angles.
He also defeats his own claims to supernatural levels of precision when he claims that they are within a micron “in places” so what are they within in all of the other places?
people often get confused with claims like “an impressive degree of accuracy” hell, even today in most applications 1/16" is considered “an impressive degree of accuracy” and when the experts talk about it, they are talking about them in context. a modern expert claiming that something built with “an impressive degree of accuracy” is most often talking about for the time.
The vikings had some of the greatest navigators on the planet, in context its obvious that i’m not suggesting they had beyond GPS level navigation. so why would anyone make that leap of judgement for cutting a bunch of rocks? impressive though they may be.
They have been opened, they are empty.