There are few questions in science as simple to state and profound in their implications as “are we alone?”—are humans the only species with a technological civilisation in the galaxy, or in the universe? This has been a matter of speculation by philosophers, theologians, authors of fiction, and innumerable people gazing at the stars since antiquity, but it was only in the years after World War II, which had seen the development of high-power microwave transmitters and low-noise receivers for radar, that it dawned upon a few visionaries that this had now become a question which could be scientifically investigated.
The propagation of radio waves through the atmosphere and the interstellar medium is governed by basic laws of physics, and the advent of radio astronomy demonstrated that many objects in the sky, some very distant, could be detected in the microwave spectrum. But if we were able to detect these natural sources, suppose we connected a powerful transmitter to our radio telescope and sent a signal to a nearby star? It was easy to calculate that, given the technology of the time (around 1960), existing microwave transmitters and radio telescopes could transmit messages across interstellar distances.
But, it’s one thing to calculate that intelligent aliens with access to microwave communication technology equal or better than our own could communicate over the void between the stars, and entirely another to listen for those communications. The problems are simple to understand but forbidding to face: where do you point your antenna, and where do you tune your dial? There are on the order of a hundred billion stars in our galaxy. We now know, as early researchers suspected without evidence, that most of these stars have planets, some of which may have conditions suitable for the evolution of intelligent life. Suppose aliens on one of these planets reach a level of technological development where they decide to join the “Galactic Club” and transmit a beacon which simply says “Yo! Anybody out there?” (The beacon would probably announce a signal with more information which would be easy to detect once you knew where to look.) But for the beacon to work, it would have to be aimed at candidate stars where others might be listening (a beacon which broadcasted in all directions—an “omnidirectional beacon”—would require so much energy or be limited to such a short range as to be impractical for civilisations with technology comparable to our own).
Then there’s the question of how many technological communicating civilisations there are in the galaxy. Note that it isn’t enough that a civilisation have the technology which enables it to establish a beacon: it has to do so. And it is a sobering thought that more than six decades after we had the ability to send such a signal, we haven’t yet done so. The galaxy may be full of civilisations with our level of technology and above which have the same funding priorities we do and choose to spend their research budget on intersectional autoethnography of transgender marine frobdobs rather than communicating with nerdy pocket-protector types around other stars who tediously ask Big Questions.
And suppose a civilisation decides it can find the spare change to set up and operate a beacon, inviting others to contact it. How long will it continue to transmit, especially since it’s unlikely, given the finite speed of light and the vast distances between the stars, there will be a response in the near term? Before long, scruffy professors will be marching in the streets wearing frobdob hats and rainbow tentacle capes, and funding will be called into question. This is termed the “lifetime” of a communicating civilisation, or L, which is how long that civilisation transmits and listens to establish contact with others. If you make plausible assumptions for the other parameters in the Drake equation (which estimates how many communicating civilisations there are in the galaxy), a numerical coincidence results in the estimate of the number of communicating civilisations in the galaxy being roughly equal to their communicating life in years, L. So, if a typical civilisation is open to communication for, say, 10,000 years before it gives up and diverts its funds to frobdob research, there will be around 10,000 such civilisations in the galaxy. With 100 billion stars (and around as many planets which may be hosts to life), that’s a 0.00001% chance that any given star where you point your antenna may be transmitting, and that has to be multiplied by the same probability they are transmitting their beacon in your direction while you happen to be listening. It gets worse. The galaxy is huge—around 150 million light years in diameter, and our technology can only communicate with comparable civilisations out to a tiny fraction of this, say 1000 light years for high-power omnidirectional beacons, maybe ten to a hundred times that for directed beacons, but then you have the constraint that you have to be listening in their direction when they happen to be sending.
It seems hopeless. It may be. But the 1960s were a time very different from our constrained age. Back then, if you had a problem, like going to the Moon in eight years, you said, “Wow! That’s a really big nail. How big a hammer do I need to get the job done?” Toward the end of that era when everything seemed possible, NASA convened a summer seminar at Stanford University to investigate what it would take to seriously investigate the question of whether we are alone. The result was Project Cyclops: A Design Study of a System for Detecting Extraterrestrial Intelligent Life, prepared in 1971 and issued as a NASA report (no Library of Congress catalogue number or ISBN was assigned) in 1973; the link will take you to a NASA PDF scan of the original document, which is in the public domain. The project assembled leading experts in all aspects of the technologies involved: antennas, receivers, signal processing and analysis, transmission and control, and system design and costing.
They approached the problem from what might be called the “Apollo perspective”: what will it cost, given the technology we have in hand right now, to address this question and get an answer within a reasonable time? What they came up with was breathtaking, although no more so than Apollo. If you want to listen for beacons from communicating civilisations as distant as 1000 light years and incidental transmissions (“leakage”, like our own television and radar emissions) within 100 light years, you’re going to need a really big bucket to collect the signal, so they settled on 1000 dishes, each 100 metres in diameter. Putting this into perspective, 100 metres is about the largest steerable dish anybody envisioned at the time, and they wanted to build a thousand of them, densely packed.
But wait, there’s more. These 1000 dishes were not just a huge bucket for radio waves, but a phased array, where signals from all of the dishes (or a subset, used to observe multiple targets) were combined to provide the angular resolution of a single dish the size of the entire array. This required breathtaking precision of electronic design at the time which is commonplace today (although an array of 1000 dishes spread over 16 km would still give most designers pause). The signals that might be received would not be fixed in frequency, but would drift due to Doppler shifts resulting from relative motion of the transmitter and receiver. With today’s computing hardware, digging such a signal out of the raw data is something you can do on a laptop or mobile phone, but in 1971 the best solution was an optical data processor involving exposing, developing, and scanning film. It was exquisitely clever, although obsolete only a few years later, but recall the team had agreed to use only technologies which existed at the time of their design. Even more amazing (and today, almost bizarre) was the scheme to use the array as an imaging telescope. Again, with modern computers, this is a simple matter of programming, but in 1971 the designers envisioned a vast hall in which the signals from the antennas would be re-emitted by radio transmitters which would interfere in free space and produce an intensity image on an image surface where it would be measured by an array of receiver antennæ.
What would all of this cost? Lots—depending upon the assumptions used in the design (the cost was mostly driven by the antenna specifications, where extending the search to shorter wavelengths could double the cost, since antennas had to be built to greater precision) total system capital cost was estimated as between 6 and 10 billion dollars (1971). Converting this cost into 2018 dollars gives a cost between 37 and 61 billion dollars. (By comparison, the Apollo project cost around 110 billion 2018 dollars.) But since the search for a signal may “almost certainly take years, perhaps decades and possibly centuries”, that initial investment must be backed by a long-term funding commitment to continue the search, maintain the capital equipment, and upgrade it as technology matures. Given governments’ record in sustaining long-term efforts in projects which do not line politicians’ or donors’ pockets with taxpayer funds, such perseverance is not the way to bet. Perhaps participants in the study should have pondered how to incorporate sufficient opportunities for graft into the project, but even the early 1970s were still an idealistic time when we didn’t yet think that way.
This study is the founding document of much of the work in the Search for Extraterrestrial Intelligence (SETI) conducted in subsequent decades. Many researchers first realised that answering this question, “Are we alone?”, was within our technological grasp when chewing through this difficult but inspiring document. (If you have an equation or chart phobia, it’s not for you; they figure on the majority of pages.) The study has held up very well over the decades. There are a number of assumptions we might wish to revise today (for example, higher frequencies may be better for interstellar communication than were assumed at the time, and spread spectrum transmissions may be more energy efficient than the extreme narrowband beacons assumed in the Cyclops study).
Despite disposing of wealth, technological capability, and computing power of which authors of the Project Cyclops report never dreamed, we only make little plans today. Most readers of this post, in their lifetimes, have experienced the expansion of their access to knowledge in the transition from being isolated to gaining connectivity to a global, high-bandwidth network. Imagine what it means to make the step from being confined to our single planet of origin to being plugged in to the Galactic Web, exchanging what we’ve learned with a multitude of others looking at things from entirely different perspectives. Heck, you could retire the entire capital and operating cost of Project Cyclops in the first three years just from advertising revenue on frobdob videos! (Did I mention they have very large eyes which are almost all pupil? Never mind the tentacles.)
Oliver, Bernard M., John Billingham, et al. Project Cyclops [PDF]. Stanford, CA: Stanford/NASA Ames Research Center, 1971. NASA-CR-114445 N73-18822.
Here is a recent conversation among SETI researchers on the state of the art and future prospects for SETI with ground-based telescopes.
This is a two part lecture on the philosophy of the existence and search for extraterrestrial beings from antiquity to the present day.