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This article from Kevin Knuth of the University at Albany, State University of New York was originally published at The Conversation. 
Are we alone? Unfortunately, neither of the answers feel satisfactory. To be alone in this vast universe is a lonely prospect. On the other hand, if we are not alone and there is someone or something more powerful out there, that too is terrifying.
As a NASA research scientist and now a professor of physics, I attended the 2002 NASA Contact Conference, which focused on serious speculation about extraterrestrials. During the meeting a concerned participant said loudly in a sinister tone, “You have absolutely no idea what is out there!” The silence was palpable as the truth of this statement sunk in. Humans are fearful of extraterrestrials visiting Earth. Perhaps fortunately, the distances between the stars are prohibitively vast. At least this is what we novices, who are just learning to travel into space, tell ourselves.
I have always been interested in UFOs. Of course, there was the excitement that there could be aliens and other living worlds. But more exciting to me was the possibility that interstellar travel was technologically achievable.
In 1988, during my second week of graduate school at Montana State University, several students and I were discussing a recent cattle mutilation that was associated with UFOs. A physics professor joined the conversation and told us that he had colleagues working at Malmstrom Air Force Base in Great Falls, Montana, where they were having problems with UFOs shutting down nuclear missiles. At the time I thought this professor was talking nonsense.
But 20 years later, I was stunned to see a recording of a press conference featuring several former US Air Force personnel, with a couple from Malmstrom AFB, describing similar occurrences in the 1960s. Clearly there must be something to this.
With July 2 being World UFO Day, it is a good time for society to address the unsettling and refreshing fact we may not be alone. I believe we need to face the possibility that some of the strange flying objects that outperform the best aircraft in our inventory and defy explanation may indeed be visitors from afar — and there’s plenty of evidence to support UFO sightings.
The Fermi Paradox
The nuclear physicist Enrico Fermi was famous for posing thought provoking questions. In 1950, at Los Alamos National Laboratory after discussing UFOs over lunch, Fermi asked, “Where is everybody?” He estimated there were about 300 billion stars in the galaxy, many of them billions of years older than the sun, with a large percentage of them likely to host habitable planets. Even if intelligent life developed on a very small percentage of these planets, then there should be a number of intelligent civilizations in the galaxy. Depending on the assumptions, one should expect anywhere from tens to tens of thousands of civilizations.
With the rocket-based technologies that we have developed for space travel, it would take between 5 and 50 million years for a civilization like ours to colonize our Milky Way galaxy. Since this should have happened several times already in the history of our galaxy, one should wonder where is the evidence of these civilizations? This discrepancy between the expectation that there should be evidence of alien civilizations or visitations and the presumption that no visitations have been observed has been dubbed the Fermi Paradox.
Carl Sagan correctly summarized the situation by saying that “extraordinary claims require extraordinary evidence.” The problem is that there has been no single well-documented UFO encounter that would alone qualify as the smoking gun. The situation is exacerbated by the fact that many governments around the world have covered up and classified information about such encounters. But there are enough scraps of evidence that suggest that the problem needs to be open to scientific study.
UFOs, Taboo for Professional Scientists
When it comes to science, the scientific method requires hypotheses to be testable so that inferences can be verified. UFO encounters are neither controllable nor repeatable, which makes their study extremely challenging. But the real problem, in my view, is that the UFO topic is taboo.
