“Extraordinary claims require extraordinary evidence.” So said Carl Sagan. Sir Arthur Conan Doyle put these words in the mouth of his character, Sherlock Holmes in The Sign of the Four: “How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?”
Many people believe in extraordinary things. Take UFOs for instance. “UFO” is simply an abbreviation for “Unidentified Flying Object” Most people, when they use the word, don’t use it for an airplane they don’t recognize. Instead, when people say “UFO” they mean “alien space craft.”
Most scientists are very skeptical about the existence of UFO’s. How come?
Jerry Pournelle, the noted science fiction author, has enjoyed an interesting life. He has a PhD, he’s worked in politics, and he’s worked in the defense industry for Boeing and had a rather high security clearance. He does not believe in UFO’s. He’d like to, of course. Most scientists and most science fiction writers would love nothing more than to find real live aliens. But Jerry Pournelle relates an interesting story that illustrates his reasons for skepticism.
During the Cold War there were reports of UFOs in Chile and Peru witnessed by thousands. And there was even a government conspiracy and cover-up related to the incident.
There are treaties in place that stipulate that no nation may place weapons in orbit and no nation may build or test orbital bombardment systems. This was also generally interpreted to exclude what’s known as fractional orbital bombardment systems, abbreviated with the acronym, FOBS. What is an FOBS? An FOBS is a weapon that is launched into Earth orbit, but is then de-orbited and made to re-enter the atmosphere before it makes a complete circuit around the globe. The Soviets thought they could launch a missile into orbit, swing it around the South Pole and then deorbit it so it came at the US from our southern border and thus avoid all our early warning systems which were watching for Soviet missile launches from the north. One day they decided to develop and test their system, despite the treaties, and they had their dummy missiles re-enter the atmosphere over South America. They hoped no one would notice.
Unfortunately, those re-entering dummy warheads were seen by those tens of thousands of people in Peru and Chile, making it impossible to simply dismiss all the reports as hallucinations. So the KGB quickly concocted an explanation. They spread UFO stories and even made up tales of aliens being spotted.
Meanwhile, our government didn’t want the Soviets to know just how much we knew about their experiments. So the CIA did nothing to counter the Soviet rumors. Thus, the test was covered up by both the Soviets and the Americans, each for their own reasons, but with the same result: people believed they had seen “real” UFO’s.
So, when people report they have seen “UFO’s” or been abducted by aliens, or find crop circles, or mutilated cattle, most scientists are going to first consider mundane explanations for what people are reporting. Occam’s razor is an important principle for science: the idea that given a variety of competing theories to explain something, the simplest theory that covers all the facts is more likely to be correct than a more complicated theory. A corollary to Occam’s razor is that a mundane explanation is more likely to be correct than an extraordinary one.
Although science fiction authors and scientists would love it if aliens showed up, they know the odds are against it. First, the universe is extraordinarily large. Even if there are billions of inhabited planets, which is quite probable, the distances between the worlds is so large that getting from planet to planet is beyond any current or projected technology. Star Trek notwithstanding, not only don’t we have the engineering needed to travel between the stars, we don’t even have a theory that would make it possible. To go faster than the speed of light requires overcoming some very well-established physical laws that tell us it’s impossible.
Even given some breakthrough allowing travel between the stars in a reasonable time frame, there are billions of stars—400 billion just in this galaxy—and billions of habitable planets. Space travel is expensive and hard, even for the basic sort of travel we do now just in our solar system. So any space faring civilization is unlikely to have large numbers of starships, and the frequency of travel is not likely to be large, either. So what are the odds that anyone would visit our particular planet even once, let alone the dozens of times every year they would have to if all the UFO reports are of extraterrestrial origin?
While I suppose it is possible that some UFOs are actual alien visitations, more mundane explanations seem preferable at this point.