Toronto Star – 23 July 2006
On a wooded ridge in Harvard, Mass., a specially built telescope has spent the last month scanning the skies for laser signals from alien civilizations. No luck yet.
But the Oak Ridge Observatory telescope is a sign that the Search for Extraterrestrial Intelligence (SETI) is alive and well. Despite official indifference — neither the Canadian nor the United States government funds SETI research — scientists around the world continue to scan the skies, looking for proof that we are not alone in the universe.
In addition to the Oak Ridge Observatory telescope, the Allen Telescope Array this summer will begin an in-depth survey of the skies, listening for radio signals from a million different stars in a search that will take until at least 2025. By the time it’s done, we should have a better idea of whether or not anyone out there is trying to get in touch.
SETI remains a fringe discipline, partly because of what people in the field refer to as the “giggle factor.” To a lot of observers, the idea that aliens are beaming us messages seems too ridiculous to take seriously.
That was certainly the case in 1993, when the U.S. Congress cut a $12 million NASA SETI program. Sen. Richard Bryan, the Nevada Democrat who led the fight to kill the program, joked at the time that after spending millions of dollars, “we have yet to bag a single little green fellow.” For Bryan and many others, SETI gets tossed into the same mental box where they keep UFOs, Bigfoot, and Star Trek conventioneers.
In fact, the search for extraterrestrial intelligence has been a legitimate scientific enterprise from the start. In 1960, Frank Drake, at the time an astronomer at the National Radio Astronomy Observatory in Green Bank, W. Va., pointed a radio telescope at two nearby stars and listened for signals that could have been generated by intelligent beings. He didn’t find anything, but he did launch the modern search for extraterrestrial intelligence.
“It is difficult to think of another enterprise within our capability and at relatively modest cost which holds as much promise for the future of humanity,” wrote Carl Sagan, the famous astronomer and SETI enthusiast who died almost 10 years ago.
Sagan thought that technologically advanced civilizations might send important advice that would help humans to survive our technological “adolescence” without destroying the planet.
SETI also has its legitimate scientific skeptics, who think that the conditions for life are so unlikely that they must occur only rarely, or else that intelligent life is a fluke.
But for optimists, SETI has one big thing going for it: the size of the universe. With 100 billion stars in our galaxy alone, and more than 100 billion other galaxies in the universe, optimists think that life has probably developed countless times, and that some of that life is intelligent.
Drake formalized this line of thought when he came up with the Drake Equation, which calculates the number of civilizations in our galaxy that could be trying to communicate with us right now.
Start with 100 billion stars in our galaxy. Assume that 50 per cent of those have planets around them, and each of those has at least one planet capable of sustaining life. Assume that any planet that could sustain life has a 50 per cent chance of developing it, and that once life develops there is a 20 per cent chance of intelligent life evolving.
Assume that only 20 per cent of intelligent beings are interested in communicating. Then assume that those who are interested in communicating are capable of sending out signals for 10,000 years before their civilizations collapse. Using those numbers, our galaxy should contain about 1,000 alien civilizations busily beaming messages around right now.
Of course, you can monkey with those numbers any way you want; credible estimates of civilizations interested in communicating range anywhere from millions to only one: us. But working through the numbers this way convinces a lot of people that the idea isn’t totally absurd.
Most of the SETI work so far has involved listening for radio signals. One idea is that aliens would transmit their signal at or around a frequency of 1.420 gigahertz, which is the frequency emitted by hydrogen. Hydrogen is the most abundant element in the universe, and radio astronomers are often tuned in to that frequency in order to map hydrogen clouds.
Whatever frequency they used, aliens would need to make sure we recognized the signal. It seems likely that they would transmit some sort of basic mathematical information; for instance, a list of the first dozen or so prime numbers, repeated again and again.
In fact, though, almost any non-random pattern would be likely to catch our attention. It’s even possible that we’ve detected one or more of these signals already.
The most famous is the “Wow!” signal recorded by the “Big Ear” radio telescope at Ohio State University in 1977.
The 72-second signal was so startling that statistics professor Jerry R. Ehman wrote “Wow!” on the printout. But the signal was never repeated. Many other signals have gotten attention over the years but have also remained unrepeated.
`It is difficult to think of another enterprise within our capability and at relatively modest cost which holds as much promise for the future of humanity’
The late Carl Sagan
Astronomer and SETI enthusiast
SETI researchers are still listening for radio signals. For instance, the University of California at Berkeley runs the SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) project, which piggybacks observations off of the Arecibo Observatory in Puerto Rico.
Some of the raw data are seen by millions of volunteers, who download it to their home computers and analyze it using spare computing cycles. So far about five million home users have participated.
Meanwhile, the Optical SETI telescope at Oak Ridge Observatory is part of a relatively new approach to the search for extraterrestrial intelligence.
For decades, scientists assumed that visible light would be useless for communicating, since it would be too difficult to see against the background light of the transmitting planet’s nearby star.
But it turns out that by using extremely brief pulses of laser light, a beacon could outshine its nearby sun by thousands of times. The drawback is that the beacon would have to be pointed straight at us to be detected.
The idea is that anyone setting up a beacon like this would choose hundreds or thousands of likely stars, and send messages to each in turn, maybe for just a few seconds at a time.
One of the most stinging criticisms of SETI has always been the Fermi Paradox, named after physicist Enrico Fermi, who once asked the simple question, “Where are they?”
If there really are thousands or millions of civilizations out there, why haven’t we picked up any signals, despite 45 years of looking?
The answer is that we haven’t been looking hard enough, says Seth Shostak, an astronomer at the non-profit SETI Institute in Mountain View, Calif.
Until now, SETI projects have had to make do with telescopes they could borrow for a few days or weeks at a time, or else been forced to make their observations at the same time that other astronomers were looking for other things.
That means we’ve only taken a good look at a few thousand stars. But even if there were 10,000 civilizations beaming signals straight at us, with 100 billion stars in the galaxy we would have to look at a million stars before we could reasonably expect to see even one of the signals.
The new privately funded, dedicated SETI telescopes like the Allen Telescope Array and the SETI optical telescope will have the time to look at a lot of stars in the next few decades and make it much more likely that we’ll be able to detect any transmissions.
But that brings up the biggest question of all: Why would anyone bother sending a message in the first place?
The universe is such a big place that light takes years to reach us even from the nearest stars. If we do detect a signal, it’s likely to be hundreds, thousands, or even tens of thousands of years old. Why would anyone go to the time, trouble and expense of sending a signal that couldn’t be answered for thousands of years?
For one thing, an advanced civilization might not think it’s very much trouble. Shostak points out that humans have had radio for only about 100 years. We’ve had lasers for only about 50 years. Older, more advanced civilizations with better technology would find it cheap and easy to send interstellar signals. “It might be a high school science fair project for them,” he says.
And if they’re anything like us, the urge to advertise their existence will be strong. From the Egyptian pyramids to the graffiti on the wall of a downtown building, we humans seem to have a deep need to announce our existence.
We’ve even sent a few of our own signals into space. In 1974, the Arecibo radio telescope broadcasted a message to a star cluster 25,000 light years away. We’ve also packed written information and sound recordings in some of our space probes, on the off chance they’ll be picked up by other beings some day.
Although it’s hard to guess about alien psychology, this need to announce our existence might be an impulse common to intelligent beings. Like us, they might want to shout out to the Universe, “We’re here — is anyone there?”
Kurt Kleiner