Should Earth Shut the Hell Up?

Should humanity shout to the galaxy “We are here!”? Some key considerations:

1. Since we humans recently acquired our ability to shout, aliens that hear our shouts should be far older and more advanced than us. Think thousands or millions of years, not decades. We would lose any fight, and while we might learn much from them, they can learn little from us.

2. We are unsure of alien friendliness. Most might be friendly, or most might be unfriendly. It just takes one friend to send us useful information, but it just takes one enemy to destroy us.

3. Unless aliens are so ubiquitous that UFO reports are plausible, a response from aliens would take decades at least, and might take millennia or more.

4. If aliens are near enough for us to get a response within centuries, then there are at least thousands of them out there that could yell or otherwise make themselves visible. But all of them instead seem to keep quiet and hide. That seems worrisome.

5. If aliens are instead far away, then by the time any response gets here we will be extinct, or will have already learned most of what aliens could teach us. So in this case prospects for trading useful information are poor. But they might still see us as a competitive threat and try to neutralize us.

I agree with Brin; these considerations seem to make a strong, if not overwhelming, case for not yelling on purpose yet. Since we’d have to wait long for either gains or losses, and since aliens being quiet on purpose seems worrisome, then without a good reason to think aliens are quite friendly, we should wait and learn more before yelling. Astronomy is, after all, making rapid progress.

If the case for keeping quiet is plausibly strong, the case for not letting each group decide this for themselves seems overwhelming. Such decisions have global consequences. If there is opinion variation on alien friendliness, and if anyone is free to shout, then those with the most positive opinions are most likely to shout, to the plausible regret of those with median opinions. If global governance makes sense for anything, it makes sense for this.

Some say that we can’t control yells to aliens (Harrison 2014). But far fewer people can yell loudly to aliens than can add CO2 to our atmosphere. If global control of CO2 emissions is possible, controlling yells to aliens is also possible.

David Brin did, however, neglect to mention one key consideration:

6. Earth has in fact been yelling to aliens, but accidentally, such as by radar that probes planets, asteroids, and comets. Such radar is very loud, even if noticeable to any one alien for only a brief moment. Though there are disagreements on the right metric (Benford et. al. 2010), by one measure accidental yells have reached roughly a million times more possible aliens than have purposeful yells (Zaitsev 2008).

By this measure, our loudest yells come from the Arecibo radar in Puerto Rico, when used to probe asteroids and the like. It can be heard over most of our Milky Way galaxy by any one-kilometer wide antenna pointed straight at Earth for a year. The USAF PAVE military radar also yells loudly, reaching about one tenth as many possible aliens as Arecibo (Haqq-Misra et. al. 2013). (Note that ordinary radio, television, and telecommunications signals are much quieter.)

It seems that we should also worry about accidental yells, in addition to purposeful yells. Yes, some use this risk comparison as a reductio argument to excuse purposeful yells. For example:

There are some people, [Seth Shostak] acknowledges, who might worry that broadcasting “The Day the Earth Stood Still” could be inimical to our interests. He added, “I think that if these people are truly worried about such things, they might best begin by shutting down the radar at the local airport.” (Overbye 2008)

But I say: let’s reverse the reductio, and consider seriously if our accidental yells are worth the risk.

As an economist, let me try to offer an original insight: we can use the amounts that we spend on accidental yells to help guess the yell risk that we should tolerate. At least we can if we make two simple assumptions:

1. We couldn’t get much more net value out of radar sending if we spent more on it.

2. We do not now consider the risk of alerting aliens in our radar sending cost vs. value calculations.

For example, the Arecibo radar costs about $10 million per year to run, and it spends about 2% of its time in send mode. Since world income is about $85 trillion per year, we thus spend about two parts per billion of world income on the Arecibo radar in send mode. From this we might crudely estimate the net value we get from Arecibo sending to be somewhere in the ballpark of a few parts per billion of the total value the world gets each year from continuing to exist, and not being destroyed by aliens.

Actually, this number is probably an overestimate. Yes, we get more value from Arecibo than we spend on it, but this added value should be much less for the last few dollars we spend (perhaps only 20% more). After all, what we learn via radar can be learned in other ways, even if at a higher cost. And the ratio of the value the world gets from not being exterminated to world income is probably big (a factor of two or more).

Thus if the world were in a steady state of income and radar cost and sending, we might estimate that continued indefinite use of the Arecibo radar in send mode at current levels is a bad deal if, over the long run, such use increases the chance of our being destroyed by aliens by even one in a billion. (Unless there are huge chances of nice aliens giving huge gains.) That seems to me a pretty high bar; can anyone really assure us that this risk is below this threshold?

It gets worse. As the world gets richer, we are likely to continue to spend a similar fraction of world income on radar sending. But improving technology combined with increased spending on radar sending should result in more powerful radar signals, which must increase the chance that aliens hear our accidental yells. So even if our current level of yelling produces an acceptable risk of alien extermination, that level will continue to rise, and so should eventually rise to problematic levels.

Thus even if accidental yells are not a problem today, they should eventually become a problem. So we may as well start now to think about how to manage this risk. And just as we can’t trust each group that yells on purpose to decide if their yelling is worth the risk they impose on the rest of us, we also can’t trust planetary scientists or military strategists to decide if the value they produce via accidental yells is worth the risks they impose. All such parties are plausibly biased by selfish career interests.

A key relevant factor in these analyses is the fraction of aliens who are friendly. And as an economist I’m disturbed to see that a consensus apparently arose among many in this area that aliens must be overwhelmingly friendly (Harrison 2014). Most conventional social scientists I know would find this view quite implausible; they see most conflict as deeply intractable. Why is this kind-aliens view then so common?

My guess: non-social-scientists have believed modern cultural propaganda claims that our dominant cultures today have a vast moral superiority over most other cultures through history. Our media have long suggested that conflictual behaviors like greed, theft, aggression, revenge, violence, war, destruction of nature, and population growth pressures all result from “backward” mindsets from “backward” cultures. This propaganda naturally suggests that very advanced aliens must have long since eliminated such conflict. Communist SETI researchers similarly assumed aliens to be communist.

Part of the mistake here is to model behavior via a simple one-dimensional “aggression” parameter. Yes, over time violence has fallen, but we advance in part by learning to more finely condition our behavior on context. We pick fewer pointless fights, but we also more quickly take advantage of those who can’t fight back (Pfeffer 2010). Think of academics who are cordial among equals, but unfairly referee papers from rivals who can’t much retaliate. Aliens who treat their equals well may still treat humans badly.

So, bottom line: we should cut way back on accidental yelling to aliens, such as via Arecibo radar sending, if continuing at current rates would over the long run bring even a one in a billion chance of alerting aliens to come destroy us. And even if this chance is now below one in a billion, it will rise with time and eventually force us to cut back. So let’s start now to estimate such risks, and adapt our behavior accordingly.




Gregory Benford, James Benford, and Dominic Benford (2010) Searching for Cost-Optimized Interstellar Beacons. Astrobiology 10(5):491-498.

Jacob Haqq-Misra, Michael W. Busch, Sanjoy M. Som, Seth D. Baum (2013) The benefits and harm of transmitting into space. Space Policy 29:40-48.

Albert Harrison (2014) Speaking For Earth: Projecting Cultural Values Across Deep Space and Time, in ed. Douglas Vakoch, Archeology, Anthropology, and Interstellar Communication 175-190, June 1.

Dennis Overbye (2008) One Alien to Another: A Broadcast to the Stars. New York Times, December 11.

Jeffrey Pfeffer, (2010) Power: Why Some People Have It—and Others Don’t, HarperCollins, September 14.

Alexander L. Zaitsev (2008) Detection Probability of Terrestrial Radio Signals By A Hostile Super-Civilization. Journal of Radio Electronics 5.

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.