Any technology distinguishable from magic is insufficiently advanced.
Age of Reason
"So what was the Technology of the ancients capable of? Quite possibly, I believe, anything which could be imagined. Much as the properties of Magic, in fact - but perhaps it was able to construct the entire edifice of Magic from first principles."
"My strong suggestion is that magic is not the fundamental property of the Universe that we believe it to be but, rather, it is an entirely artificial construct, one assembled by our ancestors to help us all live in peace and comfort and, mostly, harmony - with one another but, more importantly, with ourselves."
"Ourselves as a species, of course, but also each of us as individuals. Magic simply means that the universe around us works in the way we would wish it to be, which is not necessarily the same as the way it actually does work. Indeed, I have evidence to suggest that nothing that Magic does for us is, in some fundamental sense, real."
"So I put it to you: suppose we accept this proposition? Oh, I'm sure all of you will wish to study the evidence I have assembled and perhaps many of you will deny even the possibility of my theory having any merit. But, for now, I beg you to accept this proposition, just as a hypothesis, and let us see where it takes us."
"So, we have to ask an even more fundamental question: why? Why the deception? Why, for the longest part of our history, have we elected, or been forced, to rely on a magical view of the universe? What is the advantage in adopting a worldview which is misleadingly false, even if it is effortlessly useful in a practical way?"
"Over the aeons, we have explored our galaxy many times. Look at some of those ruins we have encountered on planets elsewhere; those civilisations built up in splendour and sophistication, and then gone in an eye-blink. Some of their artefacts have proved to be inscrutable, entirely incomprehensible to us; some of their languages, their writings at least partially untranslatable."
"So, we are forced to conclude that at least some of those aliens, some of those strange beings whose remains we have so often encountered, must have more intelligent than us. And yet they all perished, died out, not from violence and war, not from famine and disease, but - as far as we can tell - from some kind of civilizational ennui, some failure of nerve, or spirit, or imagination. What caused this failure? Nobody seems to know for sure - although there are many theories."
"And I too have a theory, which we shall get to in just a moment."