sqrt(2) isn't controversial these days. We might even say it's "obvious", because we're all used to using it from childhood. So you might wonder why maths professors would spend effort proving it in detail. This post is an attempt to remind people that there was a time when sqrt(2) wasn't at all obvious, was controversial, and that it makes sense to see it that way. (And indeed if you go back far enough, -1 was controversial).