[SETI 50th Anniversary] Seeking Kindred Spirits in the Vast Universe

“Project Dorothy” Re-explores Extraterrestrial Civilizations

According to a report by the U.S. Space.com on November 13, 2010, on the occasion of the 50th anniversary of humanity’s “Search for Extraterrestrial Intelligence” (SETI), astronomers from multiple countries around the world launched a joint action this month to “listen for aliens,” continuing the “Project Ozma” that began in 1960. The new exploration activity, named “Project Dorothy” (Project Dorothy), was officially launched on November 5 and will last for a full month. Astronomers from Australia, Japan, South Korea, Italy, the Netherlands, France, Argentina, and the United States are participating. They will point telescopes of various sizes toward stars around the Earth in hopes of hearing “sounds from beyond the heavens” sent by extraterrestrials.

Shin Narusawa, the lead researcher from Japan who is spearheading “Project Dorothy,” pointed out: “\epsilon Eridani and \tau Ceti are the two closest Sun-like stars to Earth in the Northern Hemisphere. For half a century, they have been the best targets for SETI, symbols of ’Project Ozma,’ and are the primary subjects of this ’Project Dorothy.’ ” Frank Drake, the founder of the original “Project Ozma,” stated in a declaration, “I am deeply gratified that in this new exploration, so many outstanding scientists will use so many telescopes, equipped with today’s advanced electronic and computer equipment.” Facts show that SETI has always been a highly controversial scientific research project; some scientists believe it is a complete waste of time and money, while others believe that the detection of extraterrestrial signals will permanently change our view of the universe.

In recent decades, the level of human astronomical observation has continuously improved. In terms of observation bands, it has long expanded from visible light to infrared, ultraviolet, radio waves, X-rays, and gamma rays. Various astronomical telescopes have also moved from the ground into space. Although no direct evidence of extraterrestrial civilization has been found to date, rational scientists are convinced that life is an inevitable result of celestial evolution under certain conditions, and Earth is by no means the only celestial body in the universe with intelligent life. At a special meeting on “The Detection of Extra-Terrestrial Life and the Consequences for Science and Society” held by the Royal Society in January 2010, Professor Simon Conway Morris, an evolutionary biologist at the University of Cambridge, gave a presentation on “Predicting the Forms of Extraterrestrial Life and How to Deal with the Worst-Case Scenario.” He believes that if Darwinian evolution applies to the entire universe, then: wherever there is a suitable environment for survival in the universe, life will multiply and evolve; this is “inevitable.” If this view holds, then technological evolution is also inevitable, meaning various “alien technologies” exist. Some scientists are puzzled because humans began transmitting radio and video signals into space in the last century and have yet to receive any reply. Professor Morris explained: “Thinking from their perspective, if I were an alien, I wouldn’t know if I should pick up this ’phone call’ either.”

Is it a Mysterious Signal from Aliens?

As early as April 3, 1928, Carl Størmer, a Norwegian working in the laboratory of the Philips Company in the Netherlands, inadvertently received a set of strange radio signals with a wavelength of 31.4 meters. These signals appeared every 3 seconds with great regularity. Størmer reported this to the station director, who was extremely interested and believed the signals might come from extraterrestrials.

Consequently, they “replied” using the same 31.4-meter wavelength, transmitting a set of Morse code signals every 20 seconds. They transmitted continuously for 15 days without a reply. On the 16th day, they received that strange signal again, appearing every 3 seconds, as if someone were attempting to contact Earthlings. Størmer was overjoyed and arranged another transmission test in October of the same year, which resulted in the same wonderful signals being received again.

News of these miraculous signals caused a worldwide sensation, and many radio stations turned their attention to monitoring them. In the United States, someone reported receiving such signals 10 times between February and April 1929; a French scientific research vessel also received the same signals on May 9, 1929. Unfortunately, no one was able to decipher the information contained within these strange signals.

In 1972, Duncan Lunan, a young Scottish astronomer, accidentally discovered the precious records left by Størmer. He was immediately attracted to these signals and used modern scientific logical thinking to study them. After many sleepless nights, Lunan announced that he had deciphered the meaning of the signals: a spacecraft from a planet in the constellation Boötes was orbiting the solar system. However, how could the authenticity of Lunan’s decipherment be proven? Later, people suspected that the signals were not sent by “aliens” at all, as some radio stars naturally emit radio waves. Nevertheless, scientists were greatly inspired and felt they should take the initiative to contact extraterrestrials through radio signals.

50 Years Ago: “Project Ozma” First Explores Extraterrestrial Civilizations

The deep starry sky hides many cosmic mysteries, and the sun, moon, and stars always seem to trigger human imagination: how do civilized planets communicate? The modern era of using radio methods to “Search for Extraterrestrial Intelligence” (SETI) began in 1959. At that time, physicists Giuseppe Cocconi and Philip Morrison of Cornell University published an article in Nature pointing out the potential possibility of interstellar communication using microwaves. A young radio astronomer, Frank Drake, independently reached the same conclusion and began a microwave search of other solar systems in the spring of 1960, which became the famous Project Ozma.

The name Project Ozma comes from the Land of Oz in a fairy tale, which is said to be a very distant place in the depths of the universe inhabited by strange creatures. In reality, Drake hoped to hear the voices of extraterrestrial intelligent life. At that time, new radio telescopes and technologies emerged, increasing the sensitivity of searches by about tenfold. “The combination of new large radio telescopes and high-sensitivity receivers gave us the first opportunity to detect signals emitted from near Sun-like stars with an intensity equivalent to the radio waves we transmit into space,” Drake said more than forty years later.

At that time, Drake suggested using the largest radio telescope in the United States—the radio telescope at Green Bank, West Virginia, with an antenna diameter of 26 meters (85 feet)—to monitor two specifically chosen nearby stars: \epsilon Eridani (10.7 light-years from Earth) and \tau Ceti (11.9 light-years from Earth). He hoped to receive information from civilized life on planets near these two stars, such as “radio broadcasts” from extraterrestrial intelligence. \tau Ceti is 11.9 light-years away and resembles the Sun in many ways. If the planets around it were inhabited by aliens with a level of technology similar to humans, they might be able to transmit radio signals to contact life outside their planet.

Scientists began implementing “Project Ozma” on April 8, 1960. Starting at 4:00 AM on April 8, the National Radio Astronomy Observatory in Green Bank, West Virginia, searched cosmic space for radio waves. Scientists used the largest radio telescope at the time (26 meters in diameter) and selected a 26-centimeter wavelength to monitor the two aforementioned stars for more than three months. Unfortunately, the result was nothing—no radio signals of any value were obtained. Despite this, the significance of this monitoring cannot be underestimated, as it was the first serious attempt by Earthlings in history, opening a new era of exploring extraterrestrial civilizations through technical means. Since then, the search for extraterrestrial civilizations has gained momentum in the United States and quickly swept the globe.

The Famous “Green Bank Equation”

In 1961, Frank Drake proposed a famous equation, later known as the “Green Bank Equation,” which was the first attempt at a quantitative analysis of the search for extraterrestrial intelligent life. Below is the equation as presented: N = R \times n_e \times f_p \times f_l \times f_i \times f_e \times L

In this formula, N represents the number of planets in the Milky Way that may have high-tech civilizations. It depends on the product of the seven parameters on the right side of the equation. In this context, R represents the number of stars in the Milky Way, f_p represents the fraction of stars that have planetary systems, n_e represents the proportion of stars with planetary systems that have habitable planets, f_l represents the fraction of habitable planets that actually develop life, f_i represents the fraction of life-bearing planets that develop intelligent life, f_e represents the fraction of intelligent civilizations that develop interstellar communication capabilities, and L represents the average lifespan (or duration) of an advanced technological civilization, as only civilizations that persist for a long time can engage in interstellar contact.

Drake once used this equation to optimistically speculate that there are about 10,000 planets with advanced civilizations in the Milky Way, or about one advanced civilization for every 20 million stars; the nearest civilization might be about 1,000 light-years away. Many other astronomers and biologists have also tried to solve this equation, but the results vary greatly. Because this equation involves multiple variables—some easier to estimate and others very difficult to determine—it is actually hard to find an exact solution.

These seven parameters currently remain uncertain unknowns. Some parameters are taken as approximations (such as R), while others are purely subjective estimates (such as L). Some people use the lowest estimated values to calculate and get 400,000; using the maximum possible values for each item yields N = 50 million. This means that the number of high-tech civilized planets in the Milky Way is between 400,000 and 50 million. The famous American science writer Isaac Asimov, based on his own views, once proposed a similar formula and estimated that there are about 500,000 civilized planets in the Milky Way, meaning that for every 1 million stars in the Milky Way, there may be an average of 18 civilized worlds. American astronomer Carl Sagan’s calculation was that the Milky Way has more than 1 million civilized planets, with distances between them reaching hundreds of light-years.

Drake now believes that any existing extraterrestrial civilization is likely to be more advanced than Earth’s civilization. For aliens, a similar television era may have long since passed. Although SETI scientists have spent half a century searching numerous planets without finding any trace of aliens, Drake firmly believes that intelligent life exists beyond Earth. Drake stated that they have to repeatedly search for signals among 10 million stars, but they are currently far from reaching that signal. The technology used by aliens to manifest themselves may be beyond current human capabilities. So, how do aliens manifest themselves? Drake has two guesses: one is to use a planet as a powerful lens to amplify light and radio signals. This “gravitational lens” is sufficient to map the topography of a planet in a distant galaxy. Looking at this technology in reverse, by using the lens as a transmitter instead of a receiver, aliens could send massive powerful signals to the entire Milky Way, shouting “We are here.” This is feasible because Einstein proved that gravity can bend light. However, humans cannot yet master this technology. Another communication method is to use ultra-strong pulsed lasers to produce an ultra-strong flash, similar to the lasers currently used in nuclear fusion reactors.

In 1977, the U.S. SETI center used a large radio telescope and reportedly received the so-called “Wow!” (Wow) signal, which was a very strong radio signal lasting 72 seconds. Scientists believe the “Wow!” signal is the only information received so far that is most likely to have originated from an extraterrestrial civilization; although people have long since begun searching for such signals, they have still found nothing.

Seeking Universe “Kindred Spirits”: Monitoring Alien “Radio Waves”

At a meeting of the American Association for the Advancement of Science, Drake reflected on his research into alien signals. One reason this task is difficult is that radio telescopes must divide the observed spectrum into very fine parts for study, a process like tuning a signal on a car radio. Another reason is the trade-off between the range a telescope can observe and the degree to which it can amplify signals. Small telescopes can observe a wide range of the sky but can only detect strong signals; large telescopes can detect weaker signals but can only focus on a small area. Therefore, it is difficult for astronomers to balance the two to make both detailed and comprehensive observations.

There are at least 200 billion stars in the Milky Way, and conservative estimates suggest there should be 100,000 celestial systems similar to the solar system, but they are far apart, and current human technical means cannot achieve interstellar travel. Therefore, achieving interstellar communication first is the most effective means. The famous Soviet astrophysicist Shklovsky believed that: “Intergalactic radio communication has a significantly different and important characteristic compared to interstellar radio communication, namely, when conducting intergalactic radio communication, signals can be sent to billions of stars at once. Therefore, if even one of these stars has a highly developed civilized society around it, this signal will be discovered. In fact, in the detected galaxies, such civilized societies may be many. Therefore, when sending various directional extragalactic signals, discovering their civilized societies is ’quite certain.’ However, when transmitting a directional signal toward any single star, the probability of finding a civilization there, or life in general, is extremely small.”

How can we most effectively search for radio signals from distant extraterrestrial civilizations? Scholars of SETI have posed three basic problems: “How to search such a vast sky?”, “If looking for extraterrestrial signals, where should the radio tuner be set?”, and “How to make full use of the limited radio telescope resources available for SETI?”

In 1971, NASA scientists held a special workshop on searching for aliens, where a massive detection plan codenamed “Cyclops” (Cyclops) was proposed. Cyclops is a god from Greek mythology—a one-eyed giant—and the exploration plan borrowed his name. The “Cyclops” plan mainly involved building thousands of 100-meter-diameter radio telescope antenna arrays, completely controlled by computers, to systematically scan the entire sky to search for signals sent by aliens. It was said that within a range of 250 light-years, it could search for radio waves emitted by any celestial body (totaling more than 660). According to preliminary budgets, the plan would cost 6 billion dollars and was not implemented due to the huge cost. However, the “Cyclops” scientific and technical analysis report became the basis for a series of subsequent SETI efforts. As Americans gradually understood the bright prospects of SETI, they began new attempts.

Are Earthlings Unique in the Universe?

Dr. Jill Tarter, the current head of the SETI Institute and an American astronomer, believes that extraterrestrial civilization is difficult to define and, due to interstellar distances, impossible to detect directly; therefore, SETI projects are actually attempts to search for other distant technological evidence; our exploration has not ceased since Drake. However, the search task before us remains extremely arduous, and it cannot be overstated. All efforts in SETI over the past few decades can only be considered a peek at a cup of water in a vast ocean, and no one can judge whether there are fish in the ocean based on a cup of water. She also said that the SETI Institute has a very practical definition of intelligent life, which is the ability to build large signal transmitters. Tarter was one of the winners of the 2009 “TED” Prize. At a gathering on March 26, 2009, she told the story of human self-awareness and space exploration and pointed out the significance of the SETI project. It is to let people understand the meaning of “human” more deeply through a cosmic perspective; she also called for more people, especially young people, to join this largest development plan in history.

In her speech, she said emotionally:

“For thousands of years, we have been asking priests and philosophers to tell us whether there is other life beyond Earth. Now, we can use 21st-century technology to find out what is actually in the stars, rather than asking what we should believe. The SETI project itself does not presuppose the existence of extraterrestrial intelligence; that is only a guess or a possibility. In such a universe, it is possible for other life to exist. The numbers themselves tell us that this possibility exists. The Sun is one of 400 billion stars in the Milky Way, and we also know that many other stars have their own planetary systems. In the past 14 years, we have discovered 350 such stars, including some small planets, and the new planet announced this week, whose radius is twice that of Earth. And even if all the stars in the Milky Way have no life, there are 100 billion other galaxies besides the Milky Way, which means there are 10^{22} stars. If you laid $100,000 checks on the ground, you would have to stack them up to 6.11 million kilometers above the stage to reach 10^{22}. That would be 16 times the distance between the Earth and the Moon, or a quarter of the distance between the Earth and the Sun, so the possibility is still quite large.”

“We hope to be able to use the pattern recognition capabilities of the human eye to discover those weak or complex signals. At the same time, we also hope to inspire the next generation through such projects. We hope that some of the results we produce can serve as classroom teaching materials and be used by schools everywhere. For those students who cannot personally visit the Allen Telescope Array (ATA), we need to tell our story in a wonderful way to attract them and change their perspective.”

“In the long history of mankind, we humans have been divided into countless forms of tribes. We have divided this already small Earth into even smaller territories. But in the end, we all belong to the same tribe, which is the creatures of Earth. And SETI is a mirror; through it, we can understand ourselves through the perspective of aliens, from which we can find that the differences between us appear so small. Even if SETI accomplishes nothing else but changes the way we see ourselves, that would be one of the most memorable things in history.”

Currently, humanity is still in the initial stage of using radio methods to explore cosmic bodies and extraterrestrial civilizations. On an optical photograph of the Milky Way, thousands of stars can be seen. According to Carl Sagan’s optimistic estimate, some of these stars must be home to advanced civilizations. But which star is it? Where should our radio telescopes point? Solving this problem is very difficult. Because the celestial bodies currently studied by people using radio telescopes are not many—among the millions of stars where advanced civilizations might appear, we have studied only a few thousand.

Scientists have made such hypothetical reasoning: assuming some extraterrestrial civilizations have lived in a peaceful and prosperous environment for 1 million years, because their science and technology are extremely developed and they are fully affluent, they are also fully capable of spending huge sums of money on significant pioneering research, including attempting to establish contact with external civilized planets. They might continuously send powerful radio signals to the outside world for 1 million years; thus, assuming that in 1 million planets, a small portion is broadcasting such signals, the proportion is 1 million years divided by 4 billion years, which is 0.025. This means that currently there are 2.5 million such planets sending signals. If they are evenly distributed in the Milky Way, the distance between two adjacent ones is about 4,600 light-years. A signal sent by humans would take 4,600 years to reach the nearest alien. If they receive it and immediately send a reply, we would have to wait patiently for another 4,600 years to receive their echo! The target of “Project Ozma” is only a dozen light-years away from us; doing so might not have much significance. To make a plan similar to “Project Ozma” practically meaningful, we would have to monitor every Sun-like single star within a range of 4,600 light-years to see if it is sending meaningful signals.