Comment VOTE! Aliens, time travelers, ghosts, other... (Score 1) 300
Hypothetically, suppose we knew for a fact that some sort of seemingly aircraft-like objects were flying around that were not built by human civilization as we now know it, and are also not an unknown phenomena of nature.
All of the following explanations appear improbable in the extreme, but which explanation would you consider to be the *least* improbable?
A. Extraterrestrials (biological or robotic)
B. Time travelers
C. Travelers from an alternate dimension or alternate timeline
D. An ancient advanced civilization that has been hitherto undiscovered (for instance, living deep within the Earth's crust, or deep undersea)
E. A supernatural phenomenon such as ghosts
F. Other (explain)
Personally I think the least improbable answer is D. Not that I think that answer is within the realm of realistic, but at least it requires fewer violations of the physical laws that we know than the other explanations.