For years, scientists have been listening for faint whispers of E.T. phoning anyone in electronic earshot. Now, some researchers are hearing sounds almost as exciting - the staccato of hammers, the crackle of arc welders, and the rumble of construction equipment - that signal the building of huge new telescopes to help answer an old question: Are we alone in the galaxy?
The answer to that question looms closer, thanks to boosts in funding, facilities, astronomical discoveries, and advances in technology. Researchers say within a few years they'll be able to conduct far more exhaustive searches for civilizations beyond our solar system.
The field "is in a stage of explosive growth," says Kent Cullers, director of research and development at the SETI Institute in Mountain View, Calif. "I'm not only excited, I'm ebullient."
A decade ago, the idea of searching for intelligent life drew more sneers than cheers in some circles. Congress was skeptical. NASA ended its small-scale program, leaving the search to private efforts. Now, interest is building again.
One factor is scientific opportunity. Astronomers are finding a growing number of planets around other stars - hinting at a potentially vast number of solar systems in the galaxy. NASA is planning two telescopes specifically designed to look for Earth-like planets outside our solar system, which could allow for more-targeted searches.
Another factor is rising technological horsepower. From cheaper, faster computers to devices better able to detect and process extremely weak signals, technologies are allowing researchers to expand their searches beyond radio waves and visible light. At least two new ground-based telescopes are under construction dedicated to the search for extraterrestrial intelligence (SETI). In August, top SETI scientists will meet at Harvard University to look at potential new projects.
Yet for all their efforts, scientists have come up empty-handed. But even that serves as a goad.
"The fraction of the galaxy we've searched ... is incredibly small," Dr. Cullers says - perhaps 700 sunlike stars out of billions. "If we tie ourselves to the growth of computing, within half a century the search will be billions of times larger than it is today."
When US astronomer Frank Drake first turned a radio dish to the heavens to listen for ET signals in 1960, he tuned in only one channel, says Dan Werthimer, an astronomer and SETI pioneer at the University of California at Berkeley's Space Sciences Laboratory. In the 1970s, new receivers could monitor 100 channels at once; today, astronomers can monitor roughly 168 million channels simultaneously - and the number doubles every year, he adds.
The field is also finding new respectability. In its latest 10-year survey of key questions in astronomy and astrophysics and the experiments needed to answer them, a National Research Council panel listed a telescope being built by the SETI Institute and UC Berkeley as a project worth supporting. Although the panel has endorsed SETI efforts in previous reports, its 2001 document was the first to endorse a private, nonprofit SETI effort.
Moreover, NASA - which ended its own SETI project in 1993 after it raised some eyebrows in Congress - has included one of the SETI Institute's scientists in its virtual Astrobiology Institute.
"SETI was once a four-letter word around NASA headquarters," Cullers says. Now SETI researchers can compete for research money "under the same conditions as everyone else."
High on the list of projects is the Allen Telescope Array, a new type of radio telescope being designed for the Hat Creek observatory site run by the University of California at Berkeley. When completed, the facility will boast 350 linked dishlike antennas covering a hectare, or about 2.5 acres. Sophisticated electronics will allow observers to study signals from different objects simultaneously within the antennas' field of view. Thus, SETI astronomers can search the sky around the clock for signals from E.T. while other astronomers study interstellar clouds, hunt for dark matter, or pursue other objectives.
In March, former Microsoft executive Paul Allen announced that he was contributing $13.5 million toward the facility's expansion. An initial Paul G. Allen Foundation donation of $11.5 million is funding the first 32 antennas, expected to be installed and operating by the end of the year. This latest announcement covers another 174 dishes - if the SETI Institute and the Berkeley lab building the array can raise $16 million in matching funds.
The facility is of broad interest to radio astronomers in general because it represents an American entry in an international design competition for an even bigger array of radio telescopes covering nearly 250 acres. The Square Kilometer Array is slated to begin operating in 2020, after scientists select the site for the observatory and pick the technology that will be used. The Allen Telescope Array represents a major step forward, allowing SETI scientists to search up to 1 million stars in a fraction of the time it would take using single-observer telescopes.
Cullers notes that current research goals include giving radio-based SETI projects an ability to look for signals simultaneously in a range of different transmission modes - including more complex signals, such as those used by cellphones.
If radio has been the preferred approach for seeking out other civilizations in the galaxy, researchers also have started looking for various forms of light as a medium of communication.
Laser bursts represent one possibility, says Paul Horowitz, a physics professor at Harvard University who is hunting for E.T. with optical telescopes. With 20th-century earthbound technology, he points out, it's possible to take the most powerful lasers, generate a pulse lasting only a billionth of a second or so, then send it "backwards" through a large telescope. Viewed from afar, such a burst would be 5,000 times as bright as the sun. Because light from the laser and from the star dims at the same rate, "if you can see the star, you can see the flash," he says.
Up to now, he and his colleagues at Harvard and Princeton University have observed 15,000 stars and come up empty. But they now are building a 72-inch telescope that will allow them to survey large patches of sky at a time. They plan to begin operating the telescope - funded by a $350,000 grant from the Planetary Society in Pasadena, Calif. - within a year. Other teams at facilities such as the Lick Observatory in California are also running more selective searches.
One wavelength of emerging interest lies in infrared light, which falls just below visible light on the electromagnetic spectrum. Looking in that wavelength regime was first proposed by Freeman Dyson of the Institute for Advanced Study in Princeton, N.J. In 1959, he suggested that advanced civilizations might build orbiting habitats and solar-power stations that formed a "shell" around a star at a distance that matched that of the civilization's home planet. Such a "Dyson Sphere" would emit large amounts of infrared radiation, giving the star the appearance of emitting too much infrared light.
At the time, it sounded like an intriguing approach. But astronomers have since learned that sunlike stars - especially those with disks of dust and gas surrounding them - can appear to generate too much infrared radiation for their type.
Dr. Werthimer and colleague Charles Conroy have taken an initial crack at looking for excess IR by picking sunlike stars that are too old to have protoplanetary disks. Instead of bidding for precious telescope time, they mined data archived from surveys taken by ground- and space-based infrared telescopes.
While they found 32 stars that might have been Dyson Sphere candidates based on infrared readings alone, they found no unusual radio emissions or light pulses from 20 of the stars observed at the Arecibo Radio Telescope in Puerto Rico or from 25 of the stars viewed at optical observatories.
Other scientists are contemplating the possibility of searching for pulses from infrared lasers. Such lasers might be a preferred means of sending signals or setting up beacons across the galaxy because the light penetrates interstellar dust that can block visible light, researchers say.
Trying to expand efforts to cover a range of wavelengths and transmission types as the technology becomes available may seem like casting good money after bad. But limiting searches to one form of communication or to one type of search strategy is futile, Werthimer counters. "It's naive to think we know exactly what E.T. is doing."
• From 1947 to 1969, the US Air Force studied UFOs under Project Blue Book, headquartered at Wright-Patterson Air Force Base in Ohio. Of 12,618 total sightings reported to Project Blue Book, 701 remain unidentified.
• During several space missions, NASA astronauts reported phenomena they could not explain; NASA later determined that, in the context of space, none of the observations could be termed abnormal.
• Congress ended funding for NASA's High Resolution Microwave Survey in 1993; as a result, SETI launched the private nine-year Project Phoenix, which ended in March.
• Project Phoenix searched more than 750 nearby stars for radio signals.
Sources: NASA, SETI