Speculation is wonderful. But what about actually doing the experiment? So for over 60 years, scientists have actually been trying to communicate with extraterrestrial intelligences, mostly in the sense of listening for artificial intelligence signals from far off in space and occasionally trying to transmit a message. Probably the earliest attempt that most people are familiar with is the message in a bottle that we tossed out into the interstellar ocean, attached to the Pioneer 10 spacecraft. There was a plaque on one of the legs of that spacecraft designed by a group involving Carl Sagan, Frank Drake, and other scientists. This plaque is supposed to be a minimal representation of ourselves, to represent us to other civilizations that might encounter this object currently at a distance of 11 billion miles from earth, far beyond the orbits of Neptune and Pluto. What we see on this plaque is a human pair of figures, naked. Woman, the man, his arm raised in greeting, the silhouette of the spacecraft, and a strange star-like pattern on the left, which actually represents a map of where we are located in the galaxy in terms of nearby pulsars whose frequencies are represented in binary code along each limb of the star-like pattern. At the bottom, we see a schematic of the solar system and the rough trajectory of the spacecraft, and there's a hydrogen molecule represented at the top left. The fundamental transition of hydrogen at 1400 megahertz is considered to be one of the best places to look for an artificial signal, the so-called waterhole, a trough of radio noise in the galactic sky. It's easy to look at this and make fun of it as some people did when it was launched. NASA was criticized for sending pictures of naked people into space. Women's groups legitimately argued, why is the guy greeting everyone, the aliens, and not the woman. Also, the question arises, most people on earth probably couldn't understand some parts of this symbolism, such as the pulsar map. So how were aliens supposed to understand it? We don't even know after all if they have eyes. Despite all the criticism, it was a symbolic gesture to put this out into interstellar space. The Pioneer spacecraft is moving rapidly, but so slowly that it'll be 50 or a 100,000 years before adventures to even the nearest star, and we don't know if that system has an earth-like planet. This is not a realistic attempt at communication. Somewhat later, a second artifact was sent into space by NASA. The Voyager record, this is a gold anodized disc akin to a long-playing record, but actually playing at a half the frequency of an old fashion LP, that has coded into it information including images and musical selections. International committees were formed to produce the music and the signals on this, and in fact, the beginning has a set of greetings in 100 of the world's languages, including a message from the Secretary General of the United Nations at the time, and Jimmy Carter, the American President of the time. Once again, this attempt at communication can be criticized, not least because of the musical selections which were frozen in the late 1970s, and so [inaudible] Rap, Punk, and all sorts of musical genres. Most of musical selections were chosen by, to be blunt, older white men, and they reflect that kind of a taste. Another criticism was that we're sending into space a technology that is currently almost obsolete on the earth. Now, the scientists involved did push back against this, pointing out that current digital technologies like CDs, bubble memory, USB drives, whatever you like, are not known to be long-term stable. There's already evidence that CDs degrade after a decade. They argue that the analog technology of this record, which comes with instructions on how to play it, is actually very durable, it's been built to last 100,000 years. We can see the anthropocentric trap that lies in the heart of any attempt at communication. We have to make presumptions about aliens, their intelligence, their culture, their modes of communication. Those assumptions are likely to be wrong, but what else can we do if we're going to try and communicate? The logical scientific perspective is probably that it's much easier to detect a signal that's of artificial origin than to say what that signal means. True communication may be incredibly difficult, extremely unlikely. SETI, the Search for Extraterrestrial Intelligence has been mostly conducted at radio wavelengths. Frank Drake kicked off the subject as a young man when he conducted Project Ozma in 1959. Listening to artificial radio signals from two bright stars, he heard nothing, and he was just fitting this program into other radio astronomy programs of the telescope. Subsequently larger and more ambitious radio listening programs developed. At the SETI institute, they operate an array of antennas in the Northern California Dry Valley where the radio noise is very low. They're looking at thousands of stars simultaneously to hear radio blips and artificial signals from planets around those stars. The sensitivity of the telescopes has improved a lot in 60 years. But still, in terms of the number of possible stars, the number of possible frequencies that you can listen, and the time span, it's a small fraction of the cosmic haystack of possible communication. Radio SETI also suffered a blow in the 1980s when Congress cut it out of NASA's budget declaring it a waste of taxpayer money. NASA's charter was actually altered for about a decade to prohibit it from doing the search for extraterrestrial intelligence. The scientists who do this are accustomed to the mockery and the laughter, but they're doing it as their life's work. They're convinced that the statistics argue in favor of extraterrestrial civilizations and they think that you won't find the answer by speculation and philosophizing, they think you actually have to look. As for the fact that the technology is improving rapidly, to them, that just means the search is beginning to get interesting. After all, as Seth Shostak at the SETI institute says, "Nobody told Columbus to sit and wait at the shore with his boats because a few centuries later we'd develop aircraft." More recently, a second form of SETI has developed, Optical SETI. This requires the technology of extremely powerful pulsed lasers. If there was an intelligent civilization with such a technology near a star, the star of course would blind out the weak-reflected light from the planet, 100 million or a billion times fainter. However, we can put so much energy into a short laser pulse, that as seen from afar, it can outshine the sun for a brief fraction of a second, perhaps a nanosecond or less. Inverting this logic, we therefore think it's reasonable to look at nearby stars and sample their light characteristics very frequently, a billion times a second, looking for instance, where some artificial signal from nearby the star exceeds the light of the sun. Lasers on earth have now reached the level of almost a petawatt of power, which can be forced into a tiny interval. So this is not a silly hypothetical experiment. Radio SETI now works in similar ways, also looking for pulsed signals. Wary of the history of radio astronomy where pulsars were not anticipated and thought to be extraterrestrial intelligent signals, radio astronomers are extremely conservative over the kind of signal they would need to declare success in their search. So far, SETI has been met with 60 years of what's called the great silence. Most scientists would be discouraged after such a length of time enduring failure, but not the indomitable people like Frank Drake who do this kind of work. Frank Drake is now retired, but a whole new generation of SETI people involved in technology, radio telescope, and laser development are conducting even more ambitious searches. Microsoft co-founder Paul Allen has weighed in helping to provide funding for the array of telescopes in Northern California that's currently conducting the most sensitive search yet. The reason SETI researchers are not downcast is that information technology is working in their favor. The capability of searching frequency space is expanding exponentially with information technology and electronics. That means that the searches currently being conducted can gather more and better data in a year than in the previous half-century of searching. As a thought experiment, it's interesting to note that with the Allen Array operating in Northern California, we will be able to detect pulsed petawatt lasers, if they exist, or Arecibo type radio observatories transmitting into space around planets of any of the 100 million nearest stars. That means, if continued silence is the result of these searches, we're starting to learn something profound, perhaps these civilizations simply don't exist and we are alone. SETI, the Search for Extraterrestrial Intelligence is proceeding along two fronts. One is the search for artificial radio signals from thousands of nearby stars. The other is the search for pulsed lasers existing on planet's nearby stars where for a short instant, the light from the laser exceeds the light from the star and we can recognize that technology. By reversing logical argument, we now have the sensitivity, with our radio and optical technologies, to detect those technologies on planets around the nearest 100 million stars. If after a decade or more of searching we hear and see nothing, it may be a sign that technological civilizations are rare in the Milky Way.
