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There are few questions in our scientific inquiry into the universe and our place within it more profound than “are we alone?” As we have learned more about our world and the larger universe in which it exists, this question has become ever more fascinating. We now know that our planet, once thought the centre of the universe, is but one of what may be hundreds of billions of planets in our own galaxy, which is one of hundreds of billions of galaxies in the observable universe. Not long ago, we knew only of the planets in our own solar system, and some astronomers believed planetary systems were rare, perhaps formed by freak encounters between two stars following their orbits around the galaxy. But now, thanks to exoplanet hunters and, especially, the Kepler spacecraft, we know that it’s “planets, planets, everywhere”—most stars have planets, and many stars have planets where conditions may be suitable for the origin of life.
If this be the case, then when we gaze upward at the myriad stars in the heavens, might there be other eyes (or whatever sense organs they use for the optical spectrum) looking back from planets of those stars toward our Sun, wondering if they are alone? Many are the children, and adults, who have asked themselves that question when standing under a pristine sky. For the ten year old Jill Tarter, it set her on a path toward a career which has been almost coterminous with humanity’s efforts to discover communications from extraterrestrial civilisations—an effort which continues today, benefitting from advances in technology unimagined when she undertook the quest.
World War II had seen tremendous advancements in radio communications, in particular the short wavelengths (“microwaves”) used by radar to detect enemy aircraft and submarines. After the war, this technology provided the foundation for the new field of radio astronomy, which expanded astronomers’ window on the universe from the traditional optical spectrum into wavelengths that revealed phenomena never before observed nor, indeed, imagined, and hinted at a universe which was much larger, complicated, and violent than previously envisioned.
In 1959, Philip Morrison and Guiseppe Cocconi published a paper in Nature in which they calculated that using only technologies and instruments already existing on the Earth, intelligent extraterrestrials could send radio messages across the distances to the nearby stars, and that these messages could be received, detected, and decoded by terrestrial observers. This was the origin of SETI—the Search for Extraterrestrial Intelligence. In 1960, Frank Drake used a radio telescope to search for signals from two nearby star systems; he heard nothing.
As they say, absence of evidence is not evidence of absence, and this is acutely the case in SETI. First of all, consider that you must first decide what kind of signal aliens might send. If it’s something which can’t be distinguished from natural sources, there’s little hope you’ll be able to tease it out of the cacophony which is the radio spectrum. So we must assume they’re sending something that doesn’t appear natural. But what is the variety of natural sources? There’s a dozen or so Ph.D. projects just answering that question, including some surprising discoveries of natural sources nobody imagined, such as pulsars, which were sufficiently strange that when first observed they were called “LGM” sources for “Little Green Men”. On what frequency are they sending (in other words, where do we have to turn our dial to receive them, for those geezers who remember radios with dials)? The most efficient signals will be those with a very narrow frequency range, and there are billions of possible frequencies the aliens might choose. We could be pointed in the right place, at the right time, and simply be tuned to the wrong station.
Then there’s that question of “the right time”. It would be absurdly costly to broadcast a beacon signal in all directions at all times: that would require energy comparable to that emitted by a star (which, if you think about it, does precisely that). So it’s likely that any civilisation with energy resources comparable to our own would transmit in a narrow beam to specific targets, switching among them over time. If we didn’t happen to be listening when they were sending, we’d never know they were calling.
If you put all of these constraints together, you come up with what’s called an “observational phase space”—a multidimensional space of frequency, intensity, duration of transmission, angular extent of transmission, bandwidth, and other parameters which determine whether you’ll detect the signal. And that assumes you’re listening at all, which depends upon people coming up with the money to fund the effort and pursue it over the years.
It’s beyond daunting. The space to be searched is so large, and our ability to search it so limited, that negative results, even after decades of observation, are equivalent to walking down to the seashore, sampling a glass of ocean water, and concluding that based on the absence of fish, the ocean contained no higher life forms. But suppose you find a fish? That would change everything.
Jill Tarter began her career in the mainstream of astronomy. Her Ph.D. research at the University of California, Berkeley was on brown dwarfs (bodies more massive than gas giant planets but too small to sustain the nuclear fusion reactions which cause stars to shine—a brown dwarf emits weakly in the infrared as it slowly radiates away the heat from the gravitational contraction which formed it). Her work was supported by a federal grant, which made her uncomfortable—what relevance did brown dwarfs have to those compelled to pay taxes to fund investigating them? During her Ph.D. work, she was asked by a professor in the department to help with an aged computer she’d used in an earlier project. To acquaint her with the project, the professor asked her to read the Project Cyclops report. It was a conversion experience.
Project Cyclops was a NASA study conducted in 1971 on how to perform a definitive search for radio communications from intelligent extraterrestrials. Its report [18.2 Mb PDF], issued in 1972, remains the “bible” for radio SETI, although advances in technology, particularly in computing, have rendered some of its recommendations obsolete. The product of a NASA which was still conducting missions to the Moon, it was grandiose in scale, envisioning a large array of radio telescope dishes able to search for signals from stars up to 1000 light years in distance (note that this is still a tiny fraction of the stars in the galaxy, which is around 150,000 light years in diameter). The estimated budget for the project was between 6 and 10 billion dollars (multiply those numbers by around six to get present-day funny money) spent over a period of ten to fifteen years. The report cautioned that there was no guarantee of success during that period, and that the project should be viewed as a long-term endeavour with ongoing funding to operate the system and continue the search.
The Cyclops report arrived at a time when NASA was downsizing and scaling back its ambitions: the final three planned lunar landing missions had been cancelled in 1970, and production of additional Saturn V launch vehicles had been terminated the previous year. The budget climate wasn’t hospitable to Apollo-scale projects of any description, especially those which wouldn’t support lots of civil service and contractor jobs in the districts and states of NASA’s patrons in congress. Unsurprisingly, Project Cyclops simply landed on the pile of ambitious NASA studies that went nowhere. But to some who read it, it was an inspiration. Tarter thought, “This is the first time in history when we don’t just have to believe or not believe. Instead of just asking the priests and philosophers, we can try to find an answer. This is an old and important question, and I have the opportunity to change how we try to answer it.” While some might consider searching the sky for “little green men” frivolous and/or absurd, to Tarter this, not the arcana of brown dwarfs, was something worthy of support, and of her time and intellectual effort, “something that could impact people’s lives profoundly in a short period of time.”
The project to which Tarter had been asked to contribute, Project SERENDIP (a painful acronym of Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) was extremely modest compared to Cyclops. It had no dedicated radio telescopes at all, nor even dedicated time on existing observatories. Instead, it would “piggyback” on observations made for other purposes, listening to the feed from the telescope with an instrument designed to detect the kind of narrow-band beacons envisioned by Cyclops. To cope with the problem of not knowing the frequency on which to listen, the receiver would monitor 100 channels simultaneously. Tarter’s job was programming the PDP 8/S computer to monitor the receiver’s output and search for candidate signals. (Project SERENDIP is still in operation today, employing hardware able to simultaneously monitor 128 million channels.)
From this humble start, Tarter’s career direction was set. All of her subsequent work was in SETI. It would be a roller-coaster ride all the way. In 1975, NASA had started a modest study to research (but not build) technologies for microwave SETI searches. In 1978, the program came into the sights of senator William Proxmire, who bestowed upon it his “Golden Fleece” award. The program initially survived his ridicule, but in 1982, the budget zeroed out the project. Carl Sagan personally intervened with Proxmire, and in 1983 the funding was reinstated, continuing work on a more capable spectral analyser which could be used with existing radio telescopes.
Buffeted by the start-stop support from NASA and encouraged by Hewlett-Packard executive Bernard Oliver, a supporter of SETI from its inception, Tarter decided that SETI needed its own institutional home, one dedicated to the mission and able to seek its own funding independent of the whims of congressmen and bureaucrats. In 1984, the SETI Institute was incorporated in California. Initially funded by Oliver, over the years major contributions have been made by technology moguls including William Hewlett, David Packard, Paul Allen, Gordon Moore, and Nathan Myhrvold. The SETI Institute receives no government funding whatsoever, although some researchers in its employ, mostly those working on astrobiology, exoplanets, and other topics not directly related to SETI, are supported by research grants from NASA and the National Science Foundation. Fund raising was a skill which did not come naturally to Tarter, but it was mission critical, and so she mastered the art. Today, the SETI Institute is considered one of the most savvy privately-funded research institutions, both in seeking large donations and in grass-roots fundraising.
By the early 1990s, it appeared the pendulum had swung once again, and NASA was back in the SETI game. In 1992, a program was funded to conduct a two-pronged effort: a targeted search of 800 nearby stars, and an all-sky survey looking for stronger beacons. Both would employ what were then state-of-the-art spectrum analysers able to monitor 15 million channels simultaneously. After just a year of observations, congress once again pulled the plug. The SETI Institute would have to go it alone.
Tarter launched Project Phoenix, to continue the NASA targeted search program using the orphaned NASA spectrometer hardware and whatever telescope time could be purchased from donations to the SETI Institute. In 1995, observations resumed at the Parkes radio telescope in Australia, and subsequently a telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, and the 300 metre dish at Arecibo Observatory in Puerto Rico. The project continued through 2004.
What should SETI look like in the 21st century? Much had changed since the early days in the 1960s and 1970s. Digital electronics and computers had increased in power a billionfold, not only making it possible to scan a billion channels simultaneously and automatically search for candidate signals, but to combine the signals from a large number of independent, inexpensive antennas (essentially, glorified satellite television dishes), synthesising the aperture of a huge, budget-busting radio telescope. With progress in electronics expected to continue in the coming decades, any capital investment in antenna hardware would yield an exponentially growing science harvest as the ability to analyse its output grew over time. But to take advantage of this technological revolution, SETI could no longer rely on piggyback observations, purchased telescope time, or allocations at the whim of research institutions: “SETI needs its own telescope”—one optimised for the mission and designed to benefit from advances in electronics over its lifetime.
In a series of meetings from 1998 to 2000, the specifications of such an instrument were drawn up: 350 small antennas, each 6 metres in diameter, independently steerable (and thus able to be used all together, or in segments to simultaneously observe different targets), with electronics to combine the signals, providing an effective aperture of 900 metres with all dishes operating. With initial funding from Microsoft co-founder Paul Allen (and with his name on the project, the Allen Telescope Array), the project began construction in 2004. In 2007, observations began with the first 42 dishes. By that time, Paul Allen had lost interest in the project, and construction of additional dishes was placed on hold until a new benefactor could be found. In 2011, a funding crisis caused the facility to be placed in hibernation, and the observatory was sold to SRI International for US$ 1. Following a crowdfunding effort led by the SETI Institute, the observatory was re-opened later that year, and continues operations to this date. No additional dishes have been installed: current work concentrates on upgrading the electronics of the existing antennas to increase sensitivity.
Jill Tarter retired as co-director of the SETI Institute in 2012, but remains active in its scientific, fundraising, and outreach programs. There has never been more work in SETI underway than at the present. In addition to observations with the Allen Telescope Array, the Breakthrough Listen project, funded at US$ 100 million over ten years by Russian billionaire Yuri Milner, is using thousands of hours of time on large radio telescopes, with a goal of observing a million nearby stars and the centres of a hundred galaxies. All data are available to the public for analysis. A new frontier, unimagined in the early days of SETI, is optical SETI. A pulsed laser, focused through a telescope of modest aperture, is able to easily outshine the Sun in a detector sensitive to its wavelength and pulse duration. In the optical spectrum, there’s no need for fancy electronics to monitor a wide variety of wavelengths: all you need is a prism or diffraction grating. The SETI Institute has just successfully completed a US$ 100,000 Indiegogo campaign to crowdfund the first phase of the Laser SETI project, which has as its ultimate goal an all-sky, all-the-time search for short pulses of light which may be signals from extraterrestrials or new natural phenomena to which no existing astronomical instrument is sensitive.
People often ask Jill Tarter what it’s like to spend your entire career looking for something and not finding it. But she, and everybody involved in SETI, always knew the search would not be easy, nor likely to succeed in the short term. The reward for engaging in it is being involved in founding a new field of scientific inquiry and inventing and building the tools which allow exploring this new domain. The search is vast, and to date we have barely scratched the surface. About all we can rule out, after more than half a century, is a Star Trek-like universe where almost every star system is populated by aliens chattering away on the radio. Today, the SETI enterprise, entirely privately funded and minuscule by the standards of “big science”, is strongly coupled to the exponential growth in computing power and hence, roughly doubles its ability to search around every two years.
The question “are we alone?” is one which has profound implications either way it is answered. If we discover one or more advanced technological civilisations (and they will almost certainly be more advanced than we—we’ve only had radio for a little more than a century, and there are stars and planets in the galaxy billions of years older than ours), it will mean it’s possible to grow out of the daunting problems we face in the adolescence of our species and look forward to an exciting and potentially unbounded future. If, after exhaustive searches (which will take at least another fifty years of continued progress in expanding the search space), it looks like we’re alone, then intelligent life is so rare that we may be its only exemplar in the galaxy and, perhaps, the universe. Then, it’s up to us. Our destiny, and duty, is to ensure that this spark, lit within us, will never be extinguished.
Scoles, Sarah. Making Contact. New York: Pegasus Books, 2017. ISBN 978-1-68177-441-1.
This is a SETI Institute seminar with Jill Tarter and Sarah Scoles discussing the book, SETI, Tarter’s career, and future prospects for SETI, including the Laser SETI project.
Here is Jill Tarter’s 2009 TED talk which figures in the book. This is the debut of the new Jill Tarter without slides with dozens of bullet points. Tarter was the winner of the 2009 TED Prize.
This a lecture by Jill Tarter in 2014 at NASA Ames, “Searching for ET: An Investment in Our Long Future”:
An October, 2016 SETI Talk by Eliot Gillum describes the Laser SETI project: