This kind of scenario is at the top of my Possible Answers List at the moment. I certainly do not have enough evidence to back it up, but it seems likely to me. I suspect there are parallel ‘dimensions’ inhabiting the same space-time. Scientific theory is sniffing around the edges of this with such constructs as ‘Branes’ and I think this will be the next breakthrough in our understanding of reality—similar to the shift from Newtonian physics to relativity and quantum mechanics in the early 20th century. I don’t know how this works, but it MAY have something to do with vibration, frequency, and nutation.
The idea is that there is ‘leakage’ between these dimensions. Some of the leakages are accidental and some are intentional. When you read reports of UFOs flying by airliners at a high rate of speed seemingly oblivious to the plane’s presence, this is an example of accidental leakage. When you read of interactive encounters of the third kind, these may be examples of intentional leakage.
In nearly every contactee-type encounter the message is the same: Get rid of your nukes. Hastings shows a similar message in his work that has nothing to do with contactees at all. Now some of these encounters have become discredited, so perhaps that means they must be discounted as evidence. And clearly, some of these are copies of others. But take this at face value for the moment: Why would they care? It makes no sense at all unless they have a vested interest in keeping this planet stable. A nuclear explosion is a fundamental one in terms of the composition of reality. It’s not like dynamite blowing up; it messes with atomic structure. It may very well be that a nuclear explosion is felt across dimensions and puts these other space-time locations at risk. And THAT is why they don’t want us messing with nukes. It would be interesting to know if Iran and North Korea are experiencing encounters these days, not that either would admit to them.
It may be that such encounters are seen by us to be extra-terrestrial because that is our dominant paradigm and something these creatures would know. I forget the exact quote or who said it, but it goes something like this: “We are encountering a phenomenon that wants us to believe they are from outer space.” Since we are a space-faring species, at least in our own minds, we are much more likely to believe that scenario than fairies, kahunas, or angels.
Two points: One, it is extremely unlikely that we are from some other system ourselves. The fossil record may be sparse in places, but it still exists. There is a clear line as far back as Homo erectus and some pretty serious work further back to Homo hablis. We may certainly have been ‘tweaked’ ala 2001, but we are from here. There is no missing link and there never has been, except in popular culture. That is beyond dispute. Two, it is extremely unlikely that a past civilization on Earth has achieved the level of technical sophistication as our own. There may very well have been civilizations that achieved a Renaissance-type culture in the past (specifically 12,000 years ago, but that is another story), and it is possible other civilization had discovered other sources of power that we do not know about, but it I unlikely there was a planet-wide civilization like ours with the population in the billions. Evidence otherwise is quite anecdotal and inconclusive.
However, it is possible that some of our stories of past civilizations are actually about ones in different dimensions. If this is the case, then someone somewhere found a gateway that allows communication between them. This opens up two possibilities. One is that they can walk among us; the other is that we may walk among them. They may study us, harvest us, or think of us as theirs, but I don’t think they ‘live’ as a civilization among us. We also may have people who know the Truth, or at least a useful part of it, and they’re not talking. In other words, there’s plenty of room for your favorite conspiracy theories here.
The above is purely speculation on my part, of course. It’s a summary of a lifetime of study, but there are lots of those which have resulted in entirely wrong answers. I do think that reality can be found in that general direction. There’s more, but this post that’s probably far enough for now.