by Don Lincoln
We don’t know the fraction of planets that are potentially habitable that actually host life (f l), but it would seem that this should be fairly high. The fact that life evolved on Earth so quickly after the planet cooled enough to allow liquid water suggests that life might develop easily. One can use statistical techniques to use the period of time it took life to develop on Earth to come up with a lower limit on this fraction. Unless there are exceptional qualities of Earth that make it a nonrepresentative planet, it seems that the probability of an Earth-like planet developing life is higher than 20%.
Another poorly known factor is the fraction of planets that develop life that go on to evolve intelligent life (f i). There are two very distinct ways to think about this. The first school of thought suggests that the development of intelligence is inevitable. Proponents point to the observation of a steady increase in the intelligence of species over the course of the eons. Under this way of thinking, the formation of intelligence is approximately inevitable, given enough time. A contrasting way of thinking points to the fact that there have been millions of vertebrate species, and only humans have developed the kind of intelligence we have. If something had caused the hominid line to go extinct 100,000 years ago, there is no indication that another species would have gained intelligence in the intervening time. Another factoid is that, even though dinosaurs ruled the planet for about 150 million years, there is no evidence of significant intelligence developing during that time. This suggests that the development of intelligence is rather rare.
The fraction of intelligent and technologically advanced civilizations that will announce their presence (f c) would seem to be rather high. We have only us to use as an example. We rarely intentionally attempt to communicate with potential civilizations around adjacent stars, but we don’t have to do this intentionally. After all, since the early days of the twentieth century, mankind has been broadcasting its existence into the cosmos. Figure 7.1 shows us the radio and television bubble surrounding the Earth as of 2010.
The final factor, which is the lifetime that a civilization will emit a detectable signal (L) is also not well known. Civilizations on Earth tend to be at their peak for several hundred years, but subsequent civilizations often use technology from the antecedent civilization. Further, we don’t know for how long we will use radio and broadcast television to communicate. However, unless war decimates human life on Earth, either from atomic cataclysm, extreme and rapid environmental devastation or some sort of intentional biological warfare, it seems probable that ongoing use of radio, television, or some sort of electromagnetic emission is likely to continue for hundreds, if not thousands, of years.
Given the difficulty inherent in determining the parameters that go into the Drake equation (and even whether the equation is an appropriate mathematical representation of the question), it is inevitable that there will be ongoing uncertainty as to the number of technologically advanced civilizations we expect in our galaxy. Drake’s equation clearly assumes that the civilizations are independent, with no cross-pollination. It also doesn’t allow for a civilization that spans a large segment of the galaxy. A dispersed civilization might allow for bits and pieces of the society to go extinct, but it is more difficult to believe a thriving culture spanning millions of star systems would disappear entirely.
FIGURE 7.1. Nearby stars have been graced by our radio and television signals for nearly a century. It is easy to imagine that our first contact with Aliens will not be intentional but rather by an extraterrestrial civilization intercepting reruns of Ren and Stimpy. It’s kind of a sobering thought.
Kardashev Scale
In 1964, Nikolai Kardashev formalized the idea of variations in the level of technological achievement of extraterrestrial civilizations. He defined three distinct classes.
Level I: A civilization that can totally utilize all the energy from a star that reaches a planet
Level II: A civilization that can totally utilize the energy resources of a star
Level III: A civilization that can totally utilize the energy resources of an entire galaxy
Subsequent extensions of Level IV (utilizing the energy output of the visible universe) and Level V (utilizing the energy of the multiverse) are later modifications and rarely used.
It is perhaps obvious that a Level III civilization will be more detectable than a Level I civilization, in the same way that a spotlight is easier to view from great distances than a candle. As we read further into the searches for extraterrestrial life, we must keep in mind the fact that when we look beyond our solar system, we’re not necessarily looking for life with the same technological level as our own. It is quite possible that an extraterrestrial civilization might have a significant head start on us. To a degree, the current technological phase (i.e., the phase in which both electricity and radio have been mastered) of our civilization is only about 100 years old. Imagine the kinds of technology we might master by the year 3,000. Just a mere millennia is likely to bring us unfathomable advances. Now imagine that a civilization in our stellar neighborhood hit our level of technological development when the Neanderthals were dying out, when a lineage of Miocene ape experienced the mutations that lead to Homo sapiens, or even when the impact at Chicxulub killed the dinosaurs. Those Aliens would presumably have mastered technologies of which we can only dream (or, more likely, beyond anything we can dream of). Given the raw numbers of stars out there and working under the assumption that the Earth is not an exceptional planet, it seems inevitable that any intelligent extraterrestrial species we encounter will be more technologically advanced than us. So, what do we see?
The Big Ear
The thought of using radio to listen for life on other planets is an old one that can be traced back at least as far as Nikola Tesla. In Colorado Springs in 1899, he believed that he had perhaps established communication with extraterrestrials, although he was uncertain whether it was from Mars or Venus. (Keep in mind that this was at the height of the media frenzy about the question of canals on Mars.) He received in his equipment groups of clicks of one, two, three, or four. This was reminiscent of how the Martians communicated in the 1952 movie The Red Planet Mars (discussed in chapter 3). He wrote of the experience in the February 19, 1901, issue of Collier’s Weekly (as well as many other places; Tesla was both a technical genius and a prolific popularizer). He said, “There would be no insurmountable obstacle in constructing a machine capable of conveying a message to Mars, nor would there be any great difficulty in recording signals transmitted to us by the inhabitants of that planet.” His work in this area has long since been discredited, with many suggested explanations, the most likely of which is that he simply didn’t understand his equipment. This isn’t incredibly surprising, as Tesla’s pronouncements were often more spectacular than his accomplishments, and his accomplishments were very spectacular indeed. The most important point is that the idea of using radio to communicate to other planets has its antecedents in the very beginnings of mankind’s use of the technology.
Although Tesla’s efforts were perhaps the first, he was not alone. About two decades later, Guglielmo Marconi made similar claims. Marconi and Tesla were favorites of the media (think Steve Jobs in an era where this kind of technological innovation was rare) and received substantial attention in the press. In 1919, Marconi believed it possible that he received radio broadcasts from beyond the Earth. His evidence included simultaneous reception of signals in New York and in London, suggesting that the source was not local. Critics pointed out that radio receivers at the Eiffel Tower and in Washington, D.C., heard nothing. The New York Times had multi-week coverage of the story, often on the first page and above the fold. The editors of the New York Times suggested that perhaps it would be better if mankind did not contact life on other planets. Their reasoning was that the other life, being older and thus more advanced, would have technology far beyond ours and that mankind was not ready for it. This caution was seconded much later in the twentieth century by physic
ist Stephen Hawking, who pointed out that when an advanced culture encountered a less advanced one, the less advanced culture invariably suffered. This is another reason to think it wise to “lay low.” In retrospect, both Marconi and Tesla were monitoring frequencies that were too low to penetrate the Earth’s ionosphere, but they were still efforts that electrified the public.
The periodical Scientific American was just as cutting edge a magazine in 1919 as it is today and, within a couple of weeks, they had penned an article on Marconi’s claims, followed a couple of months later by a truly forward-thinking article. Marconi was talking about having received an occasional letter of Morse code, and Scientific American pointed out the inherent difficulties of using such a code for interplanetary communication. They went so far as to advance a way to communicate with Mars that might work, anticipating by decades a similar message broadcast from the Arecibo radio telescope in Puerto Rico. In this much later attempt, mankind intentionally beamed a signal into space with the hopes that it might one day be intercepted by extraterrestrials. Scientific American’s 1920 proposed message is shown in figure 7.2.
While the belief in Martian canals had disappeared among most scientists with the 1909 Martian opposition, the idea lived on in the public imagination for much longer. During the 1924 Martian opposition, in which Mars and Earth were particularly close, another attempt was made to search for radio signals from our neighbor planet. On August 21 to 23 (the date of the opposition), the United States declared a “National Radio Silence Day,” which was somewhat misnamed. What was actually advocated was that all radio traffic was turned off for five minutes, every hour, on the hour, over a 36 hour period. During that time, receivers were to listen to the heavens, looking for that Martian signal. The U.S. government got into the act with the chief signal officer of the army telling his radio stations to be vigilant for unusual transmissions, while the secretary of the navy directed the most powerful radio stations under his command to broadcast minimally and keep an ear out. Very few of the commercial stations complied, except one in Washington, D.C. The attempt was a dismal failure, scientifically speaking, but it was an interesting idea.
Over the course of the next few decades, the idea of interplanetary communication persisted among a few, including amateur radio operators. The simple fact was that the technology of the era was not really up to the project. Further, after 1930 or so, the scientific community had essentially dismissed the possibility of intelligent life on Mars, which meant the new goal was interstellar communication. This capability was definitely beyond the capability of the equipment of the time.
FIGURE 7.2. This figure from the March 20, 1920, issue of Scientific American shows an early attempt to design a message that would be understandable by an extraterrestrial civilization. It is hard enough for an English-only speaker to write a message that would be understood by (say) a literate person who reads only Chinese, let alone a culture that is as different from humanity as an Alien civilization is likely to be. Scientific American.
In the 1950s, the field of radio astronomy was born. Astronomers knew that astronomical bodies would emit electromagnetic radiation beyond the visible spectrum. Large radio dishes began to be built to study things like the galactic center, the sun, and similar sources. And this is where we again meet Frank Drake (of the Drake equation).
Frank Drake was a radio astronomer working to build the new 140 foot radio telescope in Green Bank, West Virginia. This huge antenna was housed at the National Radio Astronomy Observatory (NRAO) and signaled that a national decision had been made on whether it was better for a country to fund a large, central government laboratory or many, smaller research efforts, dispersed across the various universities and where individual researchers could exercise greater control over their research interests. Big won.
Drake long had an interest in searching the heavens for extraterrestrial radio signals. During some earlier astronomical research, he had picked up a transient signal that was never explained. While he was not prone to outlandish claims, the thought crossed his mind that perhaps the signal was not emitted from any transmitter on Earth. He tabled this idea while he pursued a more traditional research career. The quality of his research was what smoothed his way to a position at the newest and biggest radio facility around.
NRAO was a lively place, with groundbreaking in 1957 and construction on the 140 foot telescope beginning in 1958. A handful of physicists and buckets of money were tasked with building a breathtaking new radio astronomy laboratory. The big antenna was much bigger than earlier antennas, and its construction was plagued with more than the usual problems that come from building something never built before. Thus, in the meantime, NRAO decided to construct an 85 foot telescope, as this was much less of a technical challenge and would get the facility off and running. The 85 foot telescope started operations in early 1959.
It was the summer of 1959 before Drake could turn to his idea of using the NRAO facility to search for extraterrestrial signals. By consensus, the scientific staff agreed that (1) first priority had to go toward more traditional radio astronomy research and (2), given the potentially sensational nature of the extraterrestrial search, they should keep their efforts quiet. The idea was to do a simple search and to see what they could see without fear of interference that might accompany a negative newspaper story.
However, the world of high end scientific research was no less cutthroat in 1959 than it is today. There is a large degree to which it is true that in high stakes science, there is first and there is not-first. There is no second. In September 1959, a paper was published by two theoretically inclined physicists, Philip Morrison and Giuseppe Cocconi, which discussed how one might go about doing a radio search for extraterrestrials. Worried about losing credit for what was undoubtedly an important bit of research, Otto Struve, director of the Green Bank facility, announced the effort in a series of lectures given in November at Massachusetts Institute of Technology—just a mere two months after the theoretical paper came out. The lectures brought with them instant attention in the press. Articles in Time magazine, the New York Times, and the Saturday Review told the public that astronomers were going to try to listen for Alien broadcasts. The Saturday Review reported on Struve’s presentation: “He was struggling against going too far without falling too short of expressing what many astronomers have come to believe—that other intelligent beings share our occupancy of the cosmos, that some of them are very probably superior to us, culturally, and that our existence is suspected by if not definitely known to them.”
The response in the press was typically positive. The exposure brought with it donations of cutting-edge amplifiers, which would enhance the performance of the equipment. The era of modern searches for extraterrestrial broadcasts had begun.
The term SETI (Searches for Extraterrestrial Intelligence) was not coined until the mid-1970s, but that is exactly what Drake and colleagues were doing. Drake named the 1960 effort “Ozma” after Princess Ozma in L. Frank Baum’s sequels to The Wizard of Oz. Baum claimed to be in radio contact with Oz, which is how he learned of his stories. Drake and company were attempting to contact a land far weirder than Baum’s fictional kingdom.
On April 8, 1960, Operation Ozma began operations. The team looked at two stars, Tau Ceti and Epsilon Eridani. Both were thought to be sufficiently like our sun to be interesting. Subsequent analysis has tempered somewhat the enthusiasm for these stars, but they remain targets for modern planet-hunting attempts. While observing these stars, there appeared to have been a transient signal from Epsilon Eridani, although this signal turned out to have a terrestrial origin. The study was a first try and therefore covered a limited amount of the radio spectrum. No extraterrestrial signal was observed.
This brings up an important point. The radio spectrum is quite broad and artificial broadcasts are quite narrow. The Federal Communications Commission has allocated the range from 9 kHz to 275 GHz for use. Translated to wavelength, these radio frequencies range fro
m a fraction of an inch to a few miles in length. Although we shouldn’t expect extraterrestrials to comply with human choices, a single AM radio station can occupy about 20 kHz of that range, while an FM station can occupy 200 kHz. So, in the semi-arbitrary range used by humans, one can fit about 13 million AM stations and over a million FM ones. In order to see the technical details of a broadcast, the spectrum must be split even finer still. As we will see below, SETI searchers generally concentrate on a fraction of the possible radio spectrum, but still end up needing to simultaneously search hundreds of millions of radio channels.
While the radio spectrum is broad, the range of frequencies scientists use for SETI studies has historically been narrower. The particular range that is used has been selected to avoid frequency ranges that are noisy from naturally occurring sources. For instance, the Earth’s atmosphere radiates copiously for wavelengths below about an inch, while the galaxy radiates for wavelengths above about a foot. Although these thresholds aren’t perfectly sharp, SETI scientists listening outside this wavelength range will have to contend with a much louder “radio hiss.” Further, we should remember that NRAO was really a radio astronomy facility and not a SETI one. This is not unusual and, even today, when a new facility is built, SETI is almost always a secondary consideration. Luckily the limitations imposed by unwanted radio noise affect radio astronomers and SETI researchers equally, allowing the same equipment to be used for both goals. NRAO was funded to study astronomical phenomena and so the equipment was optimized for a radio wavelength of about 8 inches, as this would allow researchers to study interstellar hydrogen to look for magnetic fields.
