By PAUL DAVIES
Fifty years ago this week, on April 8, 1960, a little-known astronomer named Frank Drake sat at the controls of an 85-foot radio telescope at an observatory in Green Bank, W.Va., and began to sweep the skies, looking for a signal from an alien civilization. It was the start of the most ambitious scientific experiment in history.
Barely an hour had passed when the equipment suddenly went wild. A loudspeaker hooked up to the giant antenna began booming and the pen recorder gyrated manically. The radio telescope was pointed at a nearby star called Epsilon Eridani. Mr. Drake was nonplussed. Surely his quest couldn't be that easy? He was right. The commotion turned out to be a signal from a secret military radar.
The astronomer's solitary vigil lasted for a few weeks; he ran out of telescope time with little to report. Nevertheless, his pioneering effort sparked the genesis of a 50-year project known as the Search for Extraterrestrial Intelligence, now an international research program with a multimillion-dollar budget. It has included renting time on some of the biggest radio telescopes in the world—such as the 1,000-foot dish at Arecibo in Puerto Rico, featured in the James Bond movie "Golden Eye."
After five decades of patient listening, however, all the astronomers have to show for it is an eerie silence. Does that mean we are alone in the universe after all? Or might we be looking for the wrong thing in the wrong place at the wrong time?
The search for extraterrestrial intelligence, once considered a quixotic enterprise at best, has now become part of mainstream science. In the past decade or so, over 400 planets have been found orbiting nearby stars, and astronomers estimate there could be billions of Earth-like planets in the Milky Way alone. Biologists have discovered microbes living in extreme environments on Earth not unlike conditions on Mars, and have detected the molecular building blocks of life in deep space as well as in meteorites. Many scientists now maintain that the universe is teeming with life, and that some planets could harbor intelligent organisms.
Speculation about other worlds populated by sentient beings stretches back into pre-history. For millennia, the subject remained squarely in the provinces of religion and philosophy, but by the 19th century, science had become involved. Astronomical observations hinted that Mars could be a congenial abode for life, and in the 1870s the Italian astronomer Giovanni Schiaparelli fancied he could see lines on the surface of the red planet. A wealthy American writer, Percival Lowell, became fixated with the idea that Martians had built a network of canals to irrigate their parched planet, a conjecture fueled by the publication of H.G. Wells's novel "The War of the Worlds." Mr. Lowell built an observatory in Flagstaff, Ariz., specifically to map the canals and to look for other signs of Martian engineering.
Sadly for Mr. Lowell, there were no canals. Space probes sent to Mars in the 1960s found no sign of Martian engineering projects, and no sign of life either, just a freeze-dried desert bathed in deadly ultraviolet radiation.
In the next few decades, the search for radio messages from the stars was taken seriously enough to attract government funding. From 1970 to 1993, NASA spent about $78 million on projects that sought to refine Mr. Drake's trail-blazing observations, starting with a feasibility study for the construction of an array of 1,000 dishes sensitive enough to pick up routine television and radio transmissions from nearby stars. In 1992, NASA officially launched a program called the High Resolution Microwave Survey—but Congress killed it the following year, ending NASA's involvement.
Most of the funding today comes from private donations through the SETI Institute, a private nonprofit founded in 1984 in Mountain View, Calif. The jewel in its crown is the Allen Telescope Array, a $35 million dedicated network of 42 small dishes in northern California, with about $30 million of the funding contributed by Microsoft co-founder Paul Allen. The goal is to ultimately increase the network to 350 dishes. Donors on other projects have included David Packard and Bill Hewlett (co-founders of Hewlett-Packard) and Gordon Moore (co-founder of Intel).
Our own radio stations broadcast continuous narrow-band signals, that is, radio waves tuned to a sharply-defined frequency. Searches have mostly focused on something similar coming from space. The late Carl Sagan, a charismatic champion of searching for extraterrestrial signals in the 1980s, envisaged an advanced alien civilization deliberately beaming narrow-band radio messages at Earth to attract our attention. That scenario now seems very unlikely. Even optimists like Mr. Drake, still an active researcher, suppose that the nearest alien civilization would be hundreds of light years away. Because nothing travels faster than light, these hypothetical aliens would have no idea that a radio-savvy society exists on Earth yet.
A more likely sign could be a beacon, a radio source that goes bleep on a regular basis for anyone who might be listening, sweeping the plane of the Milky Way galaxy like the beam from a lighthouse. It would show up in a radio telescope as a brief pulse that repeats periodically—perhaps every few months or years.
Astronomers do occasionally detect brief radio bursts coming from space. A famous example was the so-called "Wow!" signal, recorded on Aug. 15, 1977, by Jerry Ehman using Ohio State University's Big Ear radio telescope. Mr. Ehman discovered it while perusing the antenna's computer printout, and was so excited he wrote "Wow!" in the margin. Radio pulses can arise from a variety of astronomical phenomena, ranging from spinning neutron stars to black hole explosions, but the characteristics of the Wow signal don't fit any known natural event. Nor did the pulse match a man-made disturbance. Nothing has been detected again from that part of the sky when astronomers have looked.
The logistics of building beacons have been analyzed by the astrophysicist Gregory Benford of the University of California at Irvine and his brother James Benford, an expert on high-powered beamed microwaves. The main unknown is how often a beacon would repeat, so the Benfords are urging for a systematic search to be made. It would need a dedicated set of radio telescopes, oriented to stare for years on end at a fixed patch of the sky—preferably towards the center of the galaxy, where the oldest stars are found and the most advanced and best-resourced civilizations are likely to be located.
By focusing on radio signals, however, the search for intelligent life has been extremely limited. As in forensic science, the clues left by alien activity might be very subtle and require sophisticated scientific techniques. An advanced civilization might engage in large-scale astro-engineering, reconfiguring its planetary system or even modifying its host star, effects that could be observed from Earth or near space. The physicist Freeman Dyson once suggested that an energy-hungry alien community might create a shell of material around a star to trap most of its heat and light to run its industry—a solar energy program with a vengeance. Dyson spheres would betray their existence by radiating strongly in the infrared region of the spectrum. A few searches have been made using satellite data, but without success.
If a civilization endures for long enough, it might seek to migrate beyond its planetary system and colonize, or at least explore, the galaxy. The Milky Way is huge—about 100,000 light years across—and contains 400 billion stars, but given enough time, a determined civilization could spread far and wide. Our solar system is about 4.5 billion years old, but the galaxy is much older; there were stars and planets around long before Earth even existed. There has been plenty of time for at least one of those expansionary civilizations to reach our galactic neighborhood—a prospect that once led the physicist Enrico Fermi to famously utter "Where is everybody?"
How do we know they haven't been here already?
It would be an incredible coincidence if Earth had been visited by aliens during the brief span of human history. On purely statistical grounds any visitation is likely to have been a very long time ago. To pluck a figure out of midair, imagine that an alien expedition passed our way 100 million years ago. Would any traces remain?
Not many. However, some remnants might still persist. Buried nuclear waste could be detectable even after billions of years. Large-scale mineral exploitation such as quarrying leaves distinctive scars that, in the case of Earth, would eventually become obscured by overlying strata but would still show up in geological surveys. Space probes parked in orbit round the sun might lie dormant yet intact for an immense period of time. Scientists could look for such hallmarks of alien technology on Earth and the moon, in near space, on Mars and among the asteroids.
Another physical object with enormous longevity is DNA. Our bodies contain some genes that have remained little changed in 100 million years. An alien expedition to Earth might have used biotechnology to assist with mineral processing, agriculture or environmental projects. If they modified the genomes of some terrestrial organisms for this purpose, or created their own micro-organisms from scratch, the legacy of this tampering might endure to this day, hidden in the biological record.
This leads to an even more radical proposal. Life on Earth stores genetic information in DNA. A lot of DNA seems to be junk, however. If aliens, or their robotic surrogates, long ago wanted to leave us a message, they need not have used radio waves. They could have uploaded the data into the junk DNA of terrestrial organisms. It would be the modern equivalent of a message in a bottle, with the message being encoded digitally in nucleic acid and the bottle being a living, replicating cell. (It is possible—scientists today have successfully implanted messages of as many as 100 words into the genome of bacteria.) A systematic search for gerrymandered genomes would be relatively cheap and simple. Incredibly, a handful of (unsuccessful) computer searches have already been made for the tell-tale signs of an alien greeting.
One of the hazards of searching for alien life is an inbuilt anthropocentric bias. There is a natural temptation to fall back on what we would do when trying to guess the motives and activities of aliens. But this is almost certainly misleading. Unless alien communities inevitably destroy themselves, they could last for tens of millions of years or more. It is impossible for us to guess what such immensely long-lived civilizations would be like or how they would affect their environment.
One thing seems clear, though. Biological intelligence is likely to be merely a brief phase in the evolution of intelligence in the universe. Even in our own young species, computers now outperform people in arithmetic and chess, and Google is smarter than any human being on the planet. Soon, most of the mental heavy lifting will be done by designed and distributed systems, and over time those systems will themselves design better systems. Given a very long period of development, information and knowledge processing, networks could merge and in principle expand to cover the entire surface of a moon or planet. If we ever do make contact with E.T., it is unlikely to be a flesh-and-blood being with a big head, but a gigantic throbbing artificial brain. Whether such an entity, inhabiting the highest reaches of the intellectual universe, would have the slightest interest in us is moot.
We have no evidence whatsoever for any life beyond Earth, let alone intelligent life. It could be that life's origin was a stupendous fluke, and that we are alone after all. But the consequences of discovering that other intelligences exist, or have existed, are so momentous it seems worth taking a penetrating look at how we could uncover evidence for it. While astronomers painstakingly monitor the hiss and crackle of the natural universe for any hint of a signal, scientists of all disciplines should reflect on how alien technology might reveal its existence in other ways, both across the vastness of space, and in our own astronomical backyard.
For many nonscientists, the fascination with the search for extraterrestrial intelligence is its tantalizing promise of wisdom in the sky. Frank Drake has said that the search for alien intelligence is really a search for ourselves, and how we fit into the great cosmic scheme. To know that we are not the only sentient beings in a mysterious and sometimes frightening universe—that an alien community had endured for eons, overcoming multiple problems—would represent a powerful symbol of hope for mankind.
Paul Davies is author of "The Eerie Silence." He is director of the Beyond Center for Fundamental Concepts in Science at Arizona State University.
Source: The Wall Street Journal