4. The entire world is a simulation and UFOs are moving around in debug mode. The size of the simulation could be anywhere from the entire universe to the Solar

4. The entire world is a simulation and UFOs are moving around in debug mode. The size of the simulation could be anywhere from the entire universe to the Solar System (or less, if you can come up with a plausible reason why the Pioneer probes appear to continue to operate despite being outside of a smaller simulation volume). Occam's Razor would throw that one out too of course.