Back in the days of Project Ozma, radio was the only efficient method of interstellar conversation anyone could imagine. The subsequent development of powerful lasers, however, suggested another way to transmit signals between the stars. Physicists at the National Ignition Facility at Lawrence Livermore National Laboratory have built lasers that put out a beam with a petawatt, or 1015 watts, of power. “A nanosecond pulse from one of these lasers, reflected off a 10-meter telescope mirror like the one in the Keck telescope, would outshine all of the light from a star by a thousandfold,” Drake says. “If ETs are sending those signals out, we have phototubes that could detect them.”
Even a modest telescope can detect millions of stars, which means it could also pick up any flashes of light that outshine those stars. Drake has conducted a large optical SETI, or OSETI, search, looking for spots of light in the sky that flicker in some meaningful way; he is seeking funding to start up a new hunt at Lick Observatory near San Jose, California. Paul Horowitz, a Harvard physicist and another SETI veteran, has been working with optical wavelengths for more than a decade and has an active OSETI project going on now. He is—of course—more enthusiastic than ever. “Charlie Townes [a pioneer in developing the laser] gave a talk several years ago,” Horowitz says, “and pointed out that if we could make lasers just an order or two of magnitude more powerful than they are today, we could create pulses that would be naked-eye visible” from a faraway planet.
Aliens would have to be only slightly more advanced than we are to have done that, yet we do not see naked-eye flashes. “You could see that as discouraging,” Horowitz says. “But I question why they would bust their asses to transmit a prodigious amount of power to make themselves visible when they could crank it down to something we could detect in maybe 20 years.” He suggests that alien civilizations might aim their messages only at civilizations more advanced than ours.
Shostak too doubts that any aliens are trying to contact us specifically. “They don’t know we exist,” he says. “I say that unequivocally. They know there’s some sort of biology here, but that’s been true for billions of years.” Only in the last 100 of those years have we developed radio transmitters. “They’re not going to waste energy signaling blue-green algae.” Instead, he thinks they might have a long list of planets that show some evidence of life and might ping each one for a millisecond or so every few days—a simple, low-effort project to see if anyone at the other end is paying attention. “If there were a bright flash tonight and another three weeks from now,” he says, “we’d study the heck out of it—and then we’d probably build a huge receiver to try and learn more.”
The overriding problem with SETI searches is that even if aliens are out there, we have no clue how they might think, what they might choose to do, or how they might do it. SETI searchers, Tarter notes, have been looking for only a limited class of signals from a very small number of stars. “Maybe we haven’t looked at enough stars or enough frequencies,” she says. “Maybe we’re not looking for the right technology because we haven’t invented it yet.”
To the SETI community, such thoughts are inspiring rather than deflating. People like Tarter and Drake consider crazy-sounding new ideas all the time; they think of it as part of their job. Back in the 1960s, for example, the physicist Freeman Dyson suggested that advanced civilizations would build shells around their suns to trap and utilize every bit of energy. Some astronomers promptly went ahead and searched for Dyson spheres, which would leak telltale infrared radiation. In his new book, The Eerie Silence, astrobiologist Paul Davies proposes looking for evidence of ETs hidden in the DNA of microbes right here on Earth. “An alien expedition to Earth might have used biotechnology to assist with mineral processing, agriculture, or environmental projects,” he writes in an essay in The Wall Street Journal. “If they modified the genomes of some terrestrial organisms for this purpose, or created their own microorganisms from scratch, the legacy of this tampering might endure to this day, hidden in the biological record.”
Some SETI ideas are so far-out that they are nearly impossible to test. The only sensible approach, Shostak suggests, is to start with the science we understand today and assume that we will be able to explore a whole lot more later. “Imagine it’s 1492,” he says. “Would you tell Columbus not to bother—that if he just waits 500 years he’ll be able to cross the ocean in six hours eating bad food?”
For now, that attitude mostly translates to bigger, better, faster, and smarter versions of the radio SETI project Frank Drake initiated in 1960. The latest tool is LOFAR, an array of 44 low-frequency radio detector stations that are being brought online across western Europe, 36 of them in the Netherlands. The relatively small, inexpensive antennas will be linked together to rival the power of the world’s biggest observatories, and part of LOFAR’s observing program will be dedicated to SETI.
A similar approach is at work at the Allen Telescope Array, a collection of 42 twenty-foot dishes located in Hat Creek, California, funded by Microsoft cofounder Paul Allen. The array began operating in 2007, using low-cost electronics to combine the input from the many radio antennas and to comb through the resulting signal, simultaneously doing conventional radio astronomy and scanning for signals from ET. Tarter, who helps manage the project, is seeking funds to increase the number of dishes to 350.
“We shouldn’t even think about getting discouraged at this point,” Shostak says, with customary verve. Horowitz amplifies that thought: “Imagine how foolish you would feel if you didn’t try only because someone said you’re a lunatic.”