The search for extraterrestrial intelligence is framed by another question that's central to astrobiology, was posed by the great physicist Enrico Fermi in 1950, long before exoplanets were discovered or we knew how much habitable real estate there really was out there in space. Fermi was a great physicist. His nickname was actually the Pope, because most of his colleagues considered him infallible on the subject of physics. Many physics undergrads learned using what are called Fermi problems, which are versions of his very quick order of magnitude estimate, way of coming to grips with a problem without doing detailed calculations or using a computer. He was an intuitive physicist. His mind was lightning quick. Fermi's logic applied to the situation of life in the universe went like this. He knew that our civilization and technology is young, and he knew that it's heading in the direction of moving beyond the Earth. A simple extrapolation of current technology, early in the space age, would argue that in some time, perhaps 100 years or 50 years, but some finite time we'll attain the capability to travel through space, at least with our robots if not ourselves. Therefore, he knew that in a fairly short period of time, travel through the galaxy was possible. He also knew that the galaxy is old. There have been Earth-like planets for billions of years, and so the odds that we were the first to attain this capability should it come soon are very low. He also knew in advance of their discovery a few decades later that it was likely that planets formed as a result of star formation and that our solar system was not unique. So he speculated that many habitable sites for life exist. Putting all these together, he came up with a question that he posed to colleagues. "Where are they?" The Fermi question has many possible answers. One popular book was written, giving 50 different answers to this question but it's a sign of the rich vein of speculation in science that can be generated by such a deceptively simple question. Some scientists doubt that there are any intelligent beings out there. One of their arguments is called Fermi's question. It's named for the Italian physicist Enrico Fermi who asked, "Where are they?" His point was that technologically advanced aliens, if they exist, should have visited Earth already. Since they evidently have not, they don't exist. I performed an experiment to test the validity of Fermi's question. At home alone one night, I decided to have lobster for dinner. So I set a place, opened the door to the street and waited for a lobster to show up and crawl onto my plate. Hours passed, at 11:00 PM I ended the experiment. No lobster had appeared so I concluded, there are no lobster on Earth. Since we know that lobster do exist, clearly there was something wrong with my reasoning. The error was of course that I'd failed to take the lobster's preferences into account. Lobster have their own agenda. They don't want to come to my house. But the fact that they don't show up doesn't mean they don't exist. As the SETI scientists like to say, "Absence of evidence isn't evidence of absence.". Of course there's a segment of the American public that believes we already know the answer to Fermi's question, that they are here or they have been here, and perhaps they're frozen somewhere in a government vault being kept secret from us. Many people know about the X files and the science fiction premises that involve alien visitation to the level where some people think it's unexceptional to believe in such ideas. Astronomers often have to wrestle with the difficulty of explaining why they think that UFOs are not alien visitations. It's particularly interesting because most astronomers are compelled by the statistics of exoplanets and the likelihood that there are habitable planets and perhaps intelligent civilizations out there. The distinction is that they think these civilizations are likely to be far away, thousands or tens of thousands of light years away, and they don't believe that they visited. The reason they don't believe is that the bar is set very high in this subject. As Carl Sagan said, "Extraordinary claims require extraordinary evidence." Just as astrobiologists will have to clear this high bar when they claim bio-marker detection on an exoplanet and the first indication of life beyond Earth, so UFO enthusiasts must clear this high bar when they present evidence of an alien visitation. Through the history of UFO work, of course most of the evidence involved anecdotal evidence or photographs, we all know even before Photoshop how easy it is to alter a photograph and that's got even easier with digital techniques. An anecdotal evidence is just that scientists will only be convinced by physical artifact or physical proof of something that cannot be explained with any other hypothesis. Even within the realm of UFO sightings, it's possible to analyze the data scientifically, approach it skeptically and decide that something other than visiting aliens is responsible for these sightings. For example a long time-span view of UFO sightings since 1947, which is the famous Roswell incident, shows that there are peaks in the time over decades. UFO sightings are not randomly distributed over time. Many of the highest peaks have been when something important is happening in the space program. The Apollo moon landings, the Mariner first landing on Mars, and so on. None of these objects we're visible to the naked eye. What's clear is that the space program was front and center and on the front page and in people's minds and it spurred their imaginations and they were putting two and two together. When UFO sightings can be explained, which is to say, when somebody reports an exact angle in the sky and a time such that we can recreate the situation, the single largest explanation for UFOs is observations of the planet Venus. Most people are simply unfamiliar with the night sky or celestial objects, and at low angles of elevation, refraction effects can cause movement that mimics strange behavior. UFO sightings dominate in rich countries. If you look at a worldwide map of UFO sightings, strangely they stop at the Canadian and Mexican border which is hard to explain. They're also incredibly few UFO sightings in Brazil, a country with the same population as the United States. Clearly, something cultural is going on here. Something that has nothing to do with aliens. UFOs are of course the tip of an iceberg of misconceptions and pseudoscience thinking that afflicts western cultures. We live in the world's most technological society, run by science and technology, and the United States of course has incredible prowess in all fields of science and yet the belief in pseudoscience and superstition is almost at an all time high. My personal favorite is crop circles. Because I was a young boy in England when the first two guys, laborers, went out into a field and with planks pressed down wheat and then went to the pub and laughed all evening. Copycat, crop circles soon began propagating throughout England and to Canada, the United States, Australia. Now it's an elaborate realm of phenomena where people argue that mathematical theorems are being represented in the pressed crops and that only aliens can have done this work. We've seen similar arguments about the pyramids, about lines drawn straight across the plains of Mexico, and so on. Ancient astronauts is a trope of pseudoscience and it really doesn't matter how many times scientists disprove the individual pieces of evidence supposedly presented, people if they want to believe will believe. Meanwhile, the real subject of intelligent life in the universe and the possibility of extraterrestrial civilizations remains out there for the taking, but we need scientific observations to decide. Among the possible responses to Fermi's well-posed question, "Where are they?" Let us consider a few even though we can't decide among them. One possibility, logically is that they do not exist at least within our galaxy. That the contingencies of evolution are such that the advancement to intelligence and technology is extraordinarily rare and we are unique in the galaxy, that cannot be disproven at this point. A related hypothesis is that they're very rare. The civilizations are rare enough that they're far distributed in time and space. What this may mean is that if the average age of a civilization is less than about 3,000 years and they're randomly distributed through the galaxy, the average civilization cannot have real-time communication or contemporaneous communication with a neighbor because the civilizations don't live long enough. Space may indeed contain the runes or signals from long dead civilizations but actual communication will not be possible. Another possibility that we must take seriously, given the possibility of weird forms of biology is that there's simply unrecognizable or that they're inscrutable in the sense that artificial signals may contain meaningful information that we simply can't recognize or understand. Communication is likely to be very difficult to aliens of unknown function and form. Another possibility, slightly bruising to our egos is that they exist and don't care. A variant of this is the Zoo Hypothesis beloved of science fiction writers, where the intelligent aliens are out there and watching us. A variant of the variant is the Berserker Hypothesis which says that as soon as we emerge from our technological adolescent and get a little dangerous, they'll swoop in and eradicate us. These are science fiction ideas of course but it is certainly possible that they don't care. Imagine by analogy that we go to the surface of an exoplanet and we find microbes, simple bacteria perhaps unusual bacteria and not like terrestrial bacteria, we would be excited, a biologist certainly would be and we'd write it down in our notebooks. But it's not exceptional enough to get us really interested. Well, if the aliens are to us as we are to bacteria, advanced by several billion years from us, they might consider us as we consider bacteria, not really very interesting. A final variation tangents into religion. The idea that super advanced civilizations do exist and that they actually created us. Regardless of the outcome, the Fermi question, "Where are they?" is well posed because there's so much habitable real estate and so much time for intelligence and technology and space travel to develop. There are many ways to answer Fermi's question. Currently, we have no way to decide among-st the fascinating possibilities.
