Earlier quoted context omitted.
Well, there are other techniques for anything that is not a crystal, and they are similarly developed as x-ray diffraction, if nothing else, take an atomic force microscope and identify each individual atom directly. > that doesn't necessarily tell you how it was made or how it works. Absolutely, there may be materials were we don't have the slightest idea how they are made or how some property arises. But my point i…
"Identify each atom individually" won't scale very far for complex materials. In short, I think it's unwarrantedly optimistic to assume that our current lab techniques, optimized for natural and human-fabricated materials, will immediately figure out (hypothetically) alien technology. No assumption is completely safe; even "made of atoms" is not guaranteed. Probable, but not guaranteed.
How is that not guaranteed?