Well, given the fact that we still know relatively little about most of the observable universe (dark matter & energy), I don't think you can completely rule ou

Well, given the fact that we still know relatively little about most of the observable universe (dark matter & energy), I don't think you can completely rule out the several unlikely hypotheses. For example, that earlier civilizations instead of electricity used a completely different form of energy - and that basically directed their development into a completely different direction, not leaving many material artefacts. I don't believe this actually happened, but a part of me knows that I can't be 100% sure it didn't.