UFOs for the most part, come from inside the human mind. We are dependent upon our senses for detecting things, and our brains for interpreting them. Whether or not you know it, or admit it, most of your thoughts are interpretations of data your body has made for the sake of convenience. However, we are an entirely unreliable source of factual data.
But this is taking us into Psychology, and we wish to learn about Astronomy. We are intrigued by the possibility of other inhabited worlds, and guess what? They may wish to meet us, enslave us, breed with us, and take our women or worse yet, our Cadbury bars!
That said, there are at least two other sources for UFOs to originate. The first one is earth, of course. We can see clouds, aircraft, glare, shadows, lights, and reflections -almost anything that could be unidentified- up there in the sky.
The second source is space. Aside from meteors, spacecraft, and satellites mistaken for air ships of distant visitors, many people are convinced UFOs have visited earth from another world. Given that there are at least 10,000 human made objects orbiting earth, and given our tendency to be a litterbug species, some objects could occasionally flit across your field of vision.
But also in space, from much, much farther abroad, there could be travelers from another dimension. FTLT, faster than light travel, would have to employ wormholes, unknown dimensions, or technology we have not yet grasped, much less mastered. There are many quality articles on Helium that deal with string theory, transporters, and so on, to address the physics of these ideas.
Have UFOs come to take a peek at our little blue marble? Setting aside motivations, as we simply would not know them, and imagining for the moment that one of the incomprehensible methods of their arrival is being utilized, where are they from, and where are they at right now? There are as many answers as there are galaxies, out there.
Some have theorized perhaps they are close relatives that escaped before one of Earth's many mass extinctions. Perhaps technology progressed to a point where we previously mismanaged our resources, and the very dangerous thing that knowledge is. Perhaps we annihilated ourselves, but some rocket scientist types got out ahead of time. Then there is the theory that they are related to the same exogenesis species that colonized the earth long ago.
Who is to say what is just too far out? There is the Scientology, Mormon, or ancient astronaut’s theories, for example. Or, perhaps they are complete and utter strangers in every sense. In this case, it is unlikely for them to be hominids, or even bipedal. This is the basis for many a xenophobic based tale in science fiction and Hollywood.
This trend says if they don't look like us, we are not going to like them much. It says much more about us, than it does about them.
People who claim close encounters, even abductions, seem to believe visitors are from some place where there is a very clinical interest in us, in our sexuality, and in our psyches. We are very interested in these things, so is this judgment also a classical psychological projection? It's possible. But if they are intelligent and advanced enough to master inter galactic travel, they may have the same zoological interest that some of earth's best and brightest have in our creatures.
If this is the case they would have just as much reason to kidnap our dimmest as well as our brightest, our most violent, and/ or our most noble. Be on the alert for unexplained disappearances of Glen Beck, or Stephen Hawking, Osama Bin Laden, Sarah Plain, Michael Vick, Jimmy Carter, Paris Hilton, or Mel Gibson. Come to think of it, who knows what really became of Gandhi, Yoko Ono, or Nancy Grace? Let's not go into who goes into what category, only the aliens know their reasons, and classification criteria.
Still, if they are simply gathering less than choice cuts of our livestock, as is sometimes alleged, than clearly they just don't know about our chocolate.