This past weekend, I drove down the California coast with some friends to Long Beach, to bask in the geeky glory that is Star Trek: The Tour. The exhibition (which should eventually make its way around the country) features a vast array of Star Trek memorabilia guaranteed to bring a smile to the face of any Trekkie. Scattered throughout the sprawling displays were such joys as the actual Enterprise-A model from the motion picture, Q's throne of judgement, Data's disembodied head, and more phasers and tricorders than you could count. An extensive collection of costumes filled the gallery, futuristic fashions from Uhura's miniskirt to Khan's tattered rags to Troi's blue dress to Neelix's wretched space-plaid suit. But the best parts by far were the actual complete sets and set recreations, several of which were open so that you could have your photo taken on them. My friends and I reveled in our brief chance to take over the bridge of the Enterprise-D. Hey, it's about time they finally let some real astrophysicists run Starfleet. . .

On this gorgeous 80-degree SoCal February weekend, the exhibit was nonetheless packed with fans and families of all ages. What accounts for the magic of Star Trek, the way it still holds such a grip on our collective imaginations forty-two years after the first episodes aired? Partly, of course, it's the hopeful future that Roddenberry crafted. Trek is a modern-day fairy tale that encourages people to believe that someday we may indeed progress beyond most of today's problems. Partly it's the great characters that inhabit that future—the bantering trio of Kirk, Spock, and Bones; Data and his quest for humanity; Sisko's gradual growth into the responsibilities of war and prophecy. But one indispensable element is the sense of wonder that Trek conjures up so well, wonder at what else might be out there in the cosmos—and who else. The mission of the Enterprise was, after all, not merely to seek out strange new worlds, but to find out there among the stars new civilizations.

Many once-far-fetched elements of Star Trek have become reality faster than expected: We now have bluetooth phone headsets pretty close to communicator badges, and in many ways an iPhone seems higher-tech than most tricorders. As I leaned over Geordi's engineering room control table from the Enterprise D, I was struck by how we're today starting to have such multitouch interfaces on real computers. And I've already written earlier about how astronomers are finding new worlds, without leaving behind any of the comforts of Earth. So how about finding some new civilizations? Are there any out there? Have our decades of listening made any progress—or are we perhaps truly alone after all?

A Brief History of SETI

While people have dreamed and speculated about intelligent life on other worlds for millennia, the true scientific search for extraterrestrial civilizations barely predates Star Trek. The Cornell astronomer Frank Drake launched the first radio survey for alien signals in 1960, using a radio telescope at Green Bank West Virginia. Shortly thereafter, scientists at Ohio State University built the Big Ear, a 500-foot antenna dedicated entirely to surveying the skies for intelligent signals. Throughout the 1960s and 1970s, the search for extraterrestrial life slowly gained support from more astronomers. Conferences were held, books were written, and increasingly ambitious survey plans were laid. Some surveys used dedicated telescopes, like the Big Ear. Others, such as UC Berkeley's SERENDIP program, piggy-backed SETI observations alongside "regular" astronomical observations, by adding additional receivers that siphoned off portions of the radio spectrum to search for signals, without affecting any already-ongoing studies of the radio universe. In the 1980s and 1990s, rapid advances in computer technology allowed ever-larger numbers of channels to be surveyed simultaneously, eventually culminating in the Billion-channel Extraterrestrial Assay (BETA) project, led my a former professor of mine, Paul Horowitz at Harvard. For a while, at least, the future of SETI looked bright.

But all that changed, in a series of mostly unrelated setbacks and disasters in the 1990s. The decade began seemingly on a bright note, with NASA at last launching its long-planned Microwave Observing Program (MOP), a ambitious survey of some 800 nearby stars. This program used the world's largest radio telescopes (the Deep Space Network dishes used for communicating with our robotic solar system probes, plus the giant Green Bank and Arecibo telescopes) and some of the most advanced radio receiver technology ever, the result of some $60 million in development over 20 years by NASA. Yet MOP barely operated for a year before opponents in Congress, led by Senator Richard Bryan of Nevada, decided that looking for "little green men" was a waste of time, and abruptly cancelled all federal funding for SETI. MOP was dead. Shortly thereafter, the OSU Big Ear was forced to cease operations, and astoundingly was demolished to make way for a golf course. A third blow to SETI came in March of 1999, when a wind storm blew over and destroyed the 26-meter radio telescope used for the BETA project. The SETI infrastructure painstakingly built over decades seemed to be completely unravelling.

From the ashes, a Phoenix

Faced with those crippling blows—the complete cessation of all federal funding for SETI and the destruction of several major facilities—the late '90s were a pretty bleak time. But those challenges ultimately gave birth to today's SETI research programs, which are more vibrant than ever before. First, the funding crisis was overcome through an unprecedented infusion of private funds. The desire to know if there's anybody out there is so widespread that non-profits have been able to raise enough money from private donors and individual members to keep SETI alive and thriving without a dime from NASA. Two organizations in particular stand out: The SETI Institute, founded by Frank Drake and today led by Jill Tartar (who is invariably introduced as "Dr. Jill Tarter, on whom Carl Sagan based the lead character of Contact"), and the Planetary Society, founded by Sagan himself.

The SETI Institute was able to gather up all the technology developed for MOP, and recycled it into Project Phoenix, packing the equipment into mobile trailers so that it could be carted around the globe from one radio telescope to the next, traveling wherever observing time was available. By 2004, Project Phoenix had accomplished all the original goals of NASA's MOP, taking an exhaustive survey of some 800 nearby stars. Ultimately, reluctantly, astronomers were forced to conclude that our immediate galactic surroundings appear to be a very quiet neighborhood indeed.

The largest SETI program to escape doom in the 90s was Berkeley's SERENDIP program, kept alive through the budget crisis by support from the Planetary Society. By 1999, spurred on by the advances in electronics, SERENDIP IV was recording more data than ever before, dozens of gigabytes every night (and nine years ago that was a lot). But a continuing challenge for SETI has always been what frequencies to listen on. As far back as 1959, a landmark paper argued that the region of the electromagnetic spectrum best suited for signaling between the stars was that between a few MHz and perhaps 10 GHz, due to interference by interstellar plasmas or planetary atmospheres at other frequencies. There were even some arguments that the absolute best spot would be right around 1.4 GHz, the frequency of radiation commonly emitted from hydrogen (and thus presumably a frequency known to all intelligent species everywhere). That assumption is not necessarily correct—our own brightest transmissions today are military radars, at frequencies that have nothing to do with atomic hydrogen! But even if it is right, constantly changing Doppler shifts due to the Earth's motion (plus the presumed motion of any alien homeworld) tremendously complicate all searches, requiring the testing of vast numbers of frequency and Doppler settings.

By now I'm sure you've guessed where this is going. SETI@Home scarely needs an introduction. The idea of harnessing volunteer computer power across the internet to churn through SETI data was revolutionary. Project organizers initially hoped they might get a few thousand volunteers to run their analysis program plus screensaver, perhaps even tens of thousands—never expecting that more than five million people would volunteer their resources toward SETI, nor that the published counts of work completed would become so competitive they'd have to engineer redundant security protocols into the network to keep out cheaters. Even some members of Congress run SETI@Home on their computers (creating a paradoxical situation where Congress refuses to fund SETI but will in fact work on it directly!) Along the way, SETI@Home has spawned an entire zoo of 'insert-science-here'@Home projects. The inexorable march of technology continues, and even five million computers is no longer enough. A recent upgrade to the Arecibo telescope's receiver has massively increased the data stream to a thundering waterfall of 300 gigabytes per day, so the SETI folks are calling for still more volunteers. Given its wild popularity thus far, that doesn't seem too much to ask! However, SETI@Home isn't without some critics. All that volunteer labor isn't truly free: the total electricity costs from running constant computations on all those computers are estimated to be around half a billion dollars, far more than the sum total of all other SETI research ever. And of course, despite a few promising signals, it's still not found anything.

The latest SETI facility to come online is the new Allen Telescope Array in remote northern California. The ATA represents a new hybrid between SETI's dedicated telescope and piggyback methods: The observatory will be shared by "regular" astronomers and SETI reseachers, but its construction funding is largely from the SETI Institute. Without SETI support, and in particular a large donation from Microsoft's Paul Allen to the SETI Institute, the observatory wouldn't be possible at all—yet it's predicted to carry out observations of a a wide range of astrophysical phenomena across the universe. So now it's SETI that's aiding mainstream radio astronomy instead of vice versa! Its novel design may even serve as a prototype for an even more ambitious possible future telescope, the Square Kilometer Array. The ATA is built out of dozens of small radio dishes, fabricated inexpensively using commercial satellite dish technology. By eventually adding hundreds of dishes over time, the ATA will become one of the most sensitive radio telescope ever.

That's not the only neat trick, however. Like many radio observatories, the Allen Telescope Array is an interferometer. Perhaps you know that by combining the light from many small telescopes, an interferometer acts like a single large telescope whose virtual diameter is set by the overall size of the telescope array. Get more telescopes spread further apart, and you can see finer details. But what most people don't know is that the overall field of view of an interferometer is set by the diameter of the individual small telescopes, and it's an inverse relation: The smaller the individual telescopes, the larger an area of sky can be seen at once. And the ATA is revolutionary in combining many more small telescopes than ever before.

And here's the real magic: By combining the data from the different telescopes in slightly different manners, the combined beam can in effect zoom in on targets anywhere in that field of view. If you combine the same exact raw data different ways, you can zoom in on multiple targets all at the same time. So the plan for the ATA is to share all the time between SETI and mainstream radio astronomy, spending 100% of the time looking at, say, some distant galaxy, and 100% of the time listening for signals from Target star A, and 100% of the time surveying dust in a star forming cloud, and 100% of the time listening for signals from Target star B. . . The only limit to the number of beams you can synthesize simultaneously is how much computing power you can throw at the problem. The trick (and the reason this hasn't been done before) is that the computations involved are fiendishly demanding, so daunting that building the electronics required was literally impossible when the project started. The scientists involved placed their faith in Moore's law, that by the time they had finished building the antennae, computer technology would have advanced to the point that the receiver could be built—barely. With Moore's law still going strong, this is one telescope that will keep on growing. The ATA began its initial operations in October, and its hunt for alien civilizations is just beginning.

To listen, or to shout?

One thing is common to all these searches for alien signals: they are passive, merely listening to the cosmos, assuming that any aliens out there are broadcasting in our direction. The Earth is not truly silent in return, of course. Our TV signals and radio are headed ever outwards—but are getting ever fainter, as more and more communications move to cable or fiber-optics, and cell phones and HDTVs get yet more adept at hearing lower-power transmissions. If we want aliens to talk to us, should we try to talk to them first?

That's the question asked by advocates for so-called METI, Messaging to Extraterrestrial Intelligence. The idea of sending signals to aliens is almost as old as the idea of listening for them, and in fact the first intentional message was sent from Arecibo all the way back in 1974, beamed toward a cluster of stars some 25,000 light years distant. Since then, a handful of messages have been transmitted to closer stars, the first of which will arrive in 2036. And the pace of new transmissions is picking up. For instance, Alexander Zaitsev of the Russian Institute for Radio Engineering has recently begun sending messages using one of the most powerful transmitters on the planet, the Evpatoria Planetary Radar in Ukraine. He argues that unless we are willing to transmit something ourselves, we have no reason or right to expect anyone transmitting back towards us. It's even been suggested that we just broadcast the whole internet so aliens can learn about us.

But some critics warn that METI may be foolish, perhaps incredibly dangerous. In an unknown cosmos, why assume aliens are necessarily benevolent? We might find ourselves sharing the galaxy with warring ancients, Vorlons and Shadows, instead of friendly but aloof Vulcans and amorous blue Andorians. Until we know that the skies are free of berserkers hell-bent on exterminating young races, shouldn't we listen quietly, and wait, and learn? (Although others have argued that even listening might be dangerous, in case of superadvanced aliens hacking into all our computers!)

Currently, anyone can legally broadcast anything they want into outer space, and there is no clear way to regulate or prevent this. OK, sure, I'll admit it seems pretty far-fetched that someone will accidentally call down an alien invasion to doom the human race, but given the completely unknown magnitude of that risk, perhaps we should at least discuss the issue. In the last few months, this debate has been coming to a boil. Last September, the International Academy of Astronautics started to address this issue by developing the so-called San Marino scale for rating how hazardous any transmission is likely to be. In October, the prestigious journal Nature published an editorial calling for all transmissions to cease until some consensus could be reached. In December, two respected senior experts resigned from the IAA's SETI working group in protest over METI advocates' refusal to end transmissions, and warned that "the civilization that blurts out its existence on interstellar beacons at the first opportunity might be like some early hominid descending from the trees and calling 'here kitty' to a saber-toothed tiger." And these are not just any old "senior experts": one is the former director of NASA's SETI office and the MOP project, and the other served as the U.S. Deputy Secretary of State for Science and Technology. The debate over METI seems to be reaching surprisingly high levels of the government!

Well, or maybe not. Amidst all this fuss and furor, without any discussion or much fanfare, NASA inexplicably decided to get into the act itself, broadcasting the first-ever transmission towards another star officially sent by the U.S. government. To celebrate the 50th anniversary of NASA's Deep Space Network radio telescopes, a four-minute-long message was beamed towards Polaris, the north star, where it will arrive in some 430 years. The message itself? NASA chose to broadcast the song "Across the Universe" by the Beatles, along with a greeting from Sir Paul McCartney himself. After all, even evil conquering alien overlords like the Beatles, right? Right? Um, we hope?