The Importance of Active SETI

A central assumption of traditional SETI listening projects is that extraterrestrials are beaming intentional signals in our direction, in an effort to make contact.[1] We humans, the less advanced civilization, are given the easier task of searching, while the older extraterrestrials take the burden of transmitting. This assumption provides the rationale for conducting exclusively passive SETI projects, rather than also engaging in active SETI—transmitting messages of our own to other possible civilizations—a practice also called Messaging to Extraterrestrial Intelligence (METI).

But suppose this assumption is wrong. Suppose that to make contact, we need to take the initiative. In the following essay, I suggest we should do just that and in the process systematically test the hypothesis that extraterrestrial intelligence may be more widespread than we typically imagine. As a result, we may increase the chances that first contact will lead to mutual comprehension.


Older Civilizations

Why would we assume that extraterrestrial civilizations are older than we are? Because it’s a prerequisite to make contact at all. Humans have had the radio technology to communicate at interstellar distances for less than a century. In the thirteen-billion-year history of the galaxy, it would be wildly improbable that their first century of communication and ours would coincide. The only way we will make contact is if they have been around much longer than we have.

If they are older, they are likely to have made contact with other extraterrestrials before us. Again, it’s a numbers game. If they make contact with us this early in our development as a technological civilization, they’ve probably done it with other civilizations before.

What does that gain us? Prior contact should give them an advantage in creating messages that we would find meaningful. Perhaps they’ve discovered that every civilization savvy enough to wield a radio telescope is also familiar with prime numbers or the periodic table of elements. And so they may tap into a cosmic Rosetta Stone through the universal language of math and science.

But it may not be so simple. Yes, stars and planets and biological organisms are made of atoms, no matter where you live in the Milky Way. But the manner in which an alien civilization represents its knowledge—even of something as universal as chemistry—may be radically different from our own.

Having been through this cosmic encounter process before, they should be better at it than we are. But will they be good enough? Will they anticipate that we are creatures who rely heavily on vision? Will they really be able to anticipate just how rudimentary our understanding of math and science is, when compared to their much longer-lived culture?

Or can we make a faster path toward mutual comprehension by telling them how we understand the universe? If much older, more experienced extraterrestrials are better at creating intelligible messages than we are, then they should also be better at comprehending our messages.

The critical question, then, is which of the following combinations yields the greatest chance for mutual comprehension:

            First, a more advanced civilization attempting to understand the message from a less advanced civilization, or

            Second, a less advanced civilization attempting to understand the message from a more advanced civilization?

If mutual comprehension is best attained when older civilizations try to understand younger civilizations, we would benefit by diversifying our search strategy to include active SETI. At a minimum it would take years or decades to receive a reply from an extraterrestrial civilization, but if the alternative is not being able to decode any messages we receive, mutual comprehension may necessitate our taking the initiative to transmit.


For Whose Benefit?

The Draft Declaration of Principles Concerning Sending Communications to Extraterrestrial Intelligence, developed within the International Academy of Astronautics (IAA) SETI Committee, stresses the benefits of an interstellar exchange for humans, rather than for our interlocutors: “The content of such a message should reflect a careful concern for the broad interests and wellbeing of Humanity….” This Draft Declaration says nothing about benefitting the extraterrestrials. While many have pondered the advantages of humankind joining the “Galactic Club” of other civilizations, no one has suggested we should pay our dues—or even apply. Through active SETI, we would do both.

Launching an active SETI program would signal our maturation as a species, as we guide our search strategies by both cosmocentric and intergenerational ethics. Such an approach would take into account the welfare of contemporary humans, as well as the extraterrestrial civilizations that may receive our messages and the far future humans who may get a reply.

Some have reasoned that the older extraterrestrial civilizations should take on the burden of transmitting, while our younger, human civilization should only listen. Whether or not older civilizations should take this responsibility, it is not clear that they will. Arguably, younger civilizations have more to gain from interstellar exchanges, so they might be expected to invest more to establish contact. Diversifying our search strategies by including active SETI may increase our long-term success, even measured solely in the benefit to humanity.


A Galactic Zoo

But is it dangerous to transmit? Would our efforts to be good galactic neighbors lead to the destruction of humankind, inviting an alien invasion? Any civilization with the capacity to travel to Earth would outstrip us technologically. If extraterrestrials could muster the resources to traverse interstellar distances, they would already know we’re here. Consider the pattern of growth we’ve seen in radio telescopes since the 1930s. If we extrapolate that growth no more than three centuries, we have radio technology capable of detecting Earth’s TV leakage at a distance of 500 light years (Shostak 2013).

But if they already know we’re here, why engage in active SETI? One possibility is the “Zoo Hypothesis,” which posits that extraterrestrials may know of our existence, but they have kept quiet, not wanting to interfere with our development as a civilization (Ball 1973). Some versions of this hypothesis would give slim hope for a response to intentional transmissions, whatever their contents. If the goal of extraterrestrials is to ensure Earth remains a pristine laboratory that they can study without external interference, we might well expect no response, because engaging with us would destroy their experiment.

Even under such a “Laboratory Hypothesis,” however, there might be ways to elicit a reply. One might imagine extraterrestrial research protocols that require silence if only undirected leakage radiation were detected, but that would authorize a reply to intentional efforts to make contact.


International Discussion

David Brin’s lead essay reviews the contentious issue of whether the International Academy of Astronautics (IAA) SETI Committee should call for international discussions prior to any active SETI transmissions. Since the 1990s the same committee has championed a protocol that guides activities following the detection of extraterrestrial intelligence. A fundamental principle of that early work was that in the event of a detection, there should be no reply prior to international consultation. So when discussions nearly two decades later turned to the question of transmissions from Earth de novo, rather than in response to the detection of another civilization, why was there reluctance—or rather, outright opposition—to including a comparable clause?

For anyone involved in the flurry of emails, there were impassioned pleas both for and against mandatory international discussions. The case in favor of consultation seems obvious: the impact of a transmission from Earth could have such profound impact that at a minimum, it deserves significant prior discussion. Why, then, did this call for international discussion fail to gain the support of the majority of the members of this committee on three separate votes?

One reason, as Brin has noted, was the lack of clarity about exactly what international discussion entails. Does this mean that there should be no intentional transmissions from Earth without endorsement of some international body, such as the United Nations? If so, this could be a cause for concern—not because anyone objected to such discussions happening, but because of the difficulty of gaining the attention of major policy and scientific organizations, especially before we have evidence that extraterrestrial intelligence exists. Would the Secretary General of the UN encourage the General Assembly to debate the wisdom of a reply from Earth, if someday SETI scientists detect a signal from afar? Perhaps. But would active SETI make it on the agenda of the General Assembly now, even before we know that life exists beyond Earth—especially when there are no ongoing transmission projects underway? Much, much less likely. So if this is what international consultation means, serious advocates of active SETI might be skittish. It’s not that international discussion at the highest level is irrelevant—but it’s very hard to achieve.

Others, I suspect, voted against adding a prohibition on transmissions on pragmatic grounds. The first protocol, outlining best practices following a signal detection, was drafted by the SETI scientists actually conducting searches. In the first iteration of this document, the scientists themselves were the signatories. That is, those signing the document were declaring what they, personally, would do in the event that they detected a signal. In the case of de novo transmissions from Earth, the guidelines were being drafted by those not directly involved in Active SETI projects.

Brin might well argue that the above objections are missing the point: that there are many reasonable definitions of international consultation, even prior to signal detection, and that the SETI Committee has the right, perhaps even the obligation, to take a stand toward best practices in SETI, even if the committee doesn’t have a capacity to enforce a ban on transmissions.

My goal is not to defend those who opposed adding a clause asking for international discussion before de novo transmissions. Admittedly, I cannot know what went through the mind of each of the 45 members of the committee as they decided how to vote. But we are left with the fact that a committee with a longstanding commitment to science policy discussions, a body of the International Academy of Astronautics, repeatedly decided not to incorporate a call for international discussions prior to de novo transmissions. And if a body with this level of commitment to SETI does not make this topic a priority, who will?

I would contend that any organization, or any individual scientist, who plans to mount an active SETI project has an obligation to foster such international discussion, even if no other international bodies will take the lead. When other international bodies are willing to participate, all the better. But a failure to gain a forum for discussion through existing scientific and policy organizations does not relieve would-be practitioners of active SETI of the obligation of fostering those discussions themselves.

What would such international discussion, fostered by organizations involved in SETI, look like in practice? Let me give two examples, both of them addressing the content of any messages that may someday be transmitted.

Last month the SETI Institute hosted a workshop called “Communicating Across the Cosmos,” which brought together a broad-based, interdisciplinary group of specialists. Over the course of two days, speakers from six countries came together to grapple with the question, “How can we make ourselves understood by other civilizations in the galaxy?” Participants represented such diverse disciplines as history, philosophy, psychology, art, linguistics, anthropology, archaeology, chemistry, astronomy, engineering, mathematics, journalism, and artificial intelligence. To ensure that these discussions could reach a wider audience, within a day of each presentation, a video of the talk and ensuing discussion was placed on the SETI Institute’s YouTube channel, freely available for anyone to view.

While international discussions of leading scholars is one important element, it’s also critical to engage the broader public. In that spirit, in 2009 the SETI Institute launched a web-based project called “Earth Speaks,” which asks people to submit the sort of messages they would want to send to an extraterrestrial civilization. To date, people from over seventy countries around the world have submitted text messages, pictures, and sound files. For the past five years, the SETI Institute has had a place where anyone, at any time, can provide input about what they would want to say. It is not a project that promises people that their messages will be transmitted, but only that their input will help inform future discussions about how we would want to present ourselves to another world (Vakoch et al. 2013).


When to Begin?

We should begin a sustained program in active SETI at this stage of the development of SETI for two reasons. First, if the objective of active SETI is to get a response from extraterrestrials for future generations of humans, then the longer we wait to begin transmitting, the longer future generations of humans will need to wait to start listening for replies.

Second, there will always be a certain arbitrariness in deciding when to begin, just as there was an arbitrariness in deciding to conduct the first passive SETI experiment, Project Ozma, over a half century ago. In retrospect, we might argue that Ozma was absurd, searching for radio transmissions from only two nearby stars, one frequency at a time. It would have made more sense, some might argue, to wait to start until astronomers could search a million or more channels, surveying thousands or millions of stars.

There are two problems with this line of reasoning. First, as far as anyone knew at the time, it was conceivable that intelligent life is so prevalent in the cosmos that almost all star systems are populated, transmitting at the selected frequency. We now know, thousands of times over, that is not the case. But that was a distinct possibility in 1960, disproved only by conducting the experiment. It’s now time to carry out an analogous active SETI project to test a similarly circumscribed hypothesis: that extraterrestrial civilizations are plentiful and ready to respond, if only we will send an intentional signal of our interest in making contact.




[1]For a more in-depth treatment of the arguments in this essay, see Vakoch, Douglas A. “Asymmetry in Active SETI: A case for transmissions from Earth.” Acta Astronautica 68.3 (2011): 476-488.



Ball, John A. “The zoo hypothesis.” Icarus 19, no. 3 (1973); 347-349.

Shostak, Seth. “Are transmissions to space dangerous?.” International Journal of Astrobiology 12, no. 1 (2013): 17-20.

Vakoch, Douglas A., Timothy A. Lower, Britton A. Niles, Katrina A. Rast, and Christopher DeCou. “What should we say to extraterrestrial intelligence?: An analysis of responses to ‘Earth Speaks’.” Acta Astronautica 86 (2013): 136-148.

Also from this issue

Lead Essay

  • David Brin criticizes the possibly reckless turn in recent SETI research. He also speculates on what the great silence may say about human societies. It may not be such a good idea to go about shouting to the cosmos - not when we have so little idea of what may be out there.

    That said, Brin speculates on the nature of any intelligent life we are likely to meet. He notes that our scientific and technological society is very unusual when compared to societies of the past: It is, he says, diamond-shaped, with relatively few at either the bottom or the top, and with a broad equality of social station, rights, and even wealth in the middle. Maintaining such a society is hard work, and one reason we seem to be alone in the universe may simply be that very few alien civilizations have escaped from feudalism or something like it.

Response Essays

  • Robin Hanson runs a cost-benefit analysis on our use of very loud radar signals. He finds that if there is even a small probability of a hostile civilization hearing us, then the risks are not worth the rewards. This conclusion holds up under fairly severe assumptions, and it grows much firmer as we consider our likely technological developments in the near future. Astronomy, moreover, is advancing rapidly, and it will likely tell us much more about the probability of existence and the nature of extraterrestrial life. When it does, we may have a better idea of the wisdom of sending out very loud radio signals. In the meantime, he concludes that yes, humanity should indeed shut the hell up.

  • We have few tools at our disposal to learn about intelligent extraterrestrials - if they even exist. But one relatively powerful tool is evolutionary psychology. Jerome H. Barkow reviews some findings from terrestrial evolutionary psychology and considers their implications for alien life. We will learn a lot if we can discover what aliens find sexy, he claims - because sexual selection has overwhelmingly influenced terrestrial animals, including ourselves.

    We will also learn a great deal by observing aliens’ predation history, their group cooperation, and their genetic transmission of culturally favored traits. Of course, these observations will have to wait for first contact. Barkow concludes by agreeing with Robin Hanson - until we know more, humanity should probably keep relatively quiet.

  • Douglas Vakoch argues that active SETI is not to be feared: If highly advanced civilizations exist out there, they will have highly advanced radio detection equipment. If they are anywhere near us, then they will have known about us for decades. Messaging them can do no more harm than what we have already done, and it may do us a great deal of good, particularly if these civilizations are waiting for us to make the first move, and if messaging them directly is the signal they need to initiate contact.