What are UFOs? I suspect the large majority of legitimate sightings involve secret military technology. It is the simplest answer, if also the most boring. However, if some UFOs are actually extraterrestrial, can we explain them with just logic? Perhaps.
Let’s assume Einstein’s theory of relativity cannot be easily surmounted, and the speed of light is a real barrier to interstellar travel (neutrinos excluded). Even if there were a technology capable of fabricating wormholes or warp space, the energies involved to move a space ship faster then light would be staggeringly enormous. Energies equal to consuming multiple stars would be necessary to create a single rudimentary wormhole. We’ve not seen any hint of this in astronomy.
Star Trek style flying cruise ships equipped with holo-decks and lounges zooming at warp speed would not seem to be economical, if even possible. I assume even advanced civilizations have economies. How much would it cost just to send biological life into space, forget even exceeding the speed of light? Would it be worth the expense if there were cheaper and equally effective means to explore the universe?
If we are being visited by extraterrestrial intelligence, then they are probably doing what we human beings have already done. Instead of sending a manned mission to Mars, we’ve sent probes, orbiters and landers. We have rovers crossing the surface of Mars, at a fraction of the cost of a manned mission. Mechanical devices don’t need food or oxygen, are immune to cosmic radiation. Humanity even has its first interstellar mission…Voyager.
I assume the same economies would apply to other worlds. I suggest UFOs are not inhabited by biological entitles, but are craft powered by artificial intelligence. For such craft, even the speed of light would not be a barrier. Artificial intelligence would essentially be immortal. If a ship traveled at half the speed of light and took hundreds of years to visit other stars, so what? An extraterrestrial civilization would simply wait for their probes to make contact, even if it took generations.
Along with self-motivated probes, we can imagine a method to instantly communicate with these probes regardless of the distance and the speed of light. It may be possible for information to be instantaneously transmitted regardless of distance using quantum entanglement. A vessel hundreds of light years away could potentially receive and transmit information without delay. If possible, why bother sending organic life?
What about the alien abduction experience? People have reported being contacted by organic aliens. Are we sure they are biological life? Take the aliens commonly called the Greys. Greys are spindly, with oversized heads and giant eyes. How do they survive on earth without a space suit? Can they breathe our air; are they immune to our germs? The size of their eyes is impossible for a living humanoid. I submit the Greys are not living beings but robots powered by A.I. Greys are like our Mars Rovers.
It may be that we’ve never met the true aliens behind the probes, and likely never will. Or perhaps an alien civilization has evolved beyond biology into singularity, becoming an immortal civilization of artificial intelligence. Then the UFO vessels may actually be the aliens!