> Very expensive and difficult to produce __is__ exotic technology.
Not in the sense of antigravity. Enough money and time can buy you an arbitrarily nice mirror, it doesn't rely on presently unknown to the public attributes of the universe.
> Enough money and time can buy you an arbitrarily nice mirror
Yes and no. But I'm going to go with mostly no. The yes is only because over thousands of years we have in fact improved mirror quality, but if we're talking about building a perfect mirror within a 5-10 year time-frame from now, it is definitely no. No matter how much money you spend.
A lot of people like to make assumptions about our capacity to build and make things. The reason we don't live in a super futuristic society isn't just because we're not dumping enough money into such a goal (obviously that would help) but because even with infinite resources we don't have great paths towards those things right now. Nuance sucks, but is necessary. The truth is that there's no such thing as "simple" when we're talking about "arbitrary precision." Honestly, not even true long before that. There's a good reason you'll find books with thousands of pages dedicated to a seemingly simple thing e.gs: o-rings, screws, bolts, threading, and so on. Don't fall for the simplicity trap.
What does "a perfect mirror" even mean? The mirrors produced for the NRO were very good but they're not alien artifacts indicating some paradigm shifting technology gap between government and the private sector. They are roughly comparable to the mirrors produced for astronomical purposes in the same era. Better because they had better funding, but not so much better that anybody should deduce that aliens had anything to do with it.
Not in the sense of antigravity. Enough money and time can buy you an arbitrarily nice mirror, it doesn't rely on presently unknown to the public attributes of the universe.