Some quick mathematical calculations gently hint that an alien invasion should not immediately wake you up.

Are we alone? It is a question that has haunted mankind for a long time. And in recent decades an answer to that question has been actively sought. For example, there are radio telescopes that scan the sky, looking for possible extraterrestrial transmissions. But we don’t just listen; In the past, people have also flung messages into space in the hope that aliens would respond. The latter approach is also known as ‘active SETI’ (where SETI stands for Search for Extra-Terrestrial Intelligence) and is not undisputed. For example, some people fear that with these messages we will – unintentionally – reveal our location to evil aliens (who may be much more intelligent and advanced than ourselves) and thereby take an incredibly big risk. Because if such a civilization with malicious intentions decides to pay us a visit, we have no chance, argue opponents of active SETI.

Small chance

But how real is that fear? Well, you don’t have to worry about it immediately, says Alberto Caballero in a study that has not yet undergone a peer review, but a preview of which has already been published. Arxiv is insightful. He relies on a series of calculations to determine how well (or badly) the evil aliens in our galaxy are represented. And the results are somewhat reassuring. For example, the chances of an evil alien blessed with a strong expansion drive intercepting our SETI messages are less than the chances of a large and catastrophic asteroid impact on Earth.

The calculations

“First, I calculated the probability that human civilization would attack an inhabited exoplanet,” Caballero said.† To this end, he looked at the number of invasions that have taken place between countries on Earth in the past hundred years. Based on the probability that humanity would attack an inhabited exoplanet, he then calculated the probability that a much more advanced alien civilization would do the same. To get a grip on the expansion drive of more advanced aliens, he once again let what we see happening on Earth. If you look at the number of invasions in the past century, you see that that number decreases as time passes and we develop further – especially in the technological field. Going by that, Caballero assumes that the urge aliens feel to attack other areas or planets also diminishes as their society becomes more sophisticated. In that case, you can therefore expect that much more advanced extraterrestrial civilizations – which are precisely thought to pose a great risk to Earth – paradoxically, so much less interested in attacking our planet.

Caballero calculated the extent to which the urge to wage war decreases as civilizations advance by looking at how the number of invasions here on Earth in a given period compares to the energy consumption (which is dictated by technological progress) in that same period. And based on those calculations, he then makes an estimate of the extent to which much more advanced aliens feel an urge to wage war. “Finally, I calculated the probability that an exoplanet to which we are sending a message harbors a civilization that could attack us. And before that, I looked again at the estimated number of extraterrestrial civilizations and potentially habitable planets in our galaxy.”

0.0000000552 percent

And so the research reveals that we have very little to fear from evil aliens. “There are an estimated 0.22 civilizations in our galaxy that are more advanced than us, capable of interstellar travel, and that would be willing to attack us,” Caballero said. The chance that we will invoke such a civilization with our active SETI is obviously small. “Based on the estimated number of potentially habitable planets in our solar system – that’s a minimum of 40 billion – and the upper bound of the estimated number of civilizations (that’s 15,785), the probability that the planet we’re sending a message to is also a civilization with malicious intent, about 0.0000000552 percent.”


And with that, the chance that with active SETI we alert an evil, advanced civilization to our existence is much smaller than the chance that a large space rock hits Earth, notes Caballero. “The probability of a Chicxulub-like asteroid (which killed 75 percent of life) is about 0.000001 percent. The chance of an alien invasion, caused by a civilization whose planet we have called upon, is therefore about two orders of magnitude smaller than the chance of a catastrophic asteroid impact.”

The calculations described above each time only consider civilizations that are much more advanced than us. When we look at civilizations that are at the same level of development as we are, the number of evil civilizations in the galaxy does increase slightly. Then there would be four malevolent alien civilizations in the galaxy. But, Caballero emphasizes, we have nothing to fear from those civilizations. “Because they wouldn’t be able to travel to our planet.”

Wood cutting

They are, of course, very entertaining mathematical calculations. But whether they also cut wood remains unclear. Because Caballero, as he himself admits, also has to make quite a few assumptions about intelligent extraterrestrial life in the absence of relevant information. The study therefore has its limitations. “The biggest one is that we don’t know the chemical makeup of alien brains,” he notes. “A wrong composition could make them psychopathic in nature. But then again, I don’t see how a mainly psychopathic species could survive long enough to evolve. On Earth, about five percent of the human population is psychopath and they run into problems all the time.”

Despite all those limitations and assumptions, there is clearly enough reason for Caballero to publish his findings. He points out, for example, that he has searched in vain for comparable studies; there has simply never been any real research as to whether our fear of evil aliens responding to our messages is justified. And once Caballero realized that, he wanted to change that. “And I couldn’t think of any other way to accomplish this study,” he says. So it’s a matter of rowing with the oars we have. “I do believe that an assessment of the risks associated with transmitting an interstellar radio message is necessary,” added Caballero. Not least because we have already sent a lot of signals into space, both intentionally and unintentionally, and therefore already run the risk that aliens notice and locate us on the basis of those signals.

But an initial assessment of the risks this poses cautiously suggests we shouldn’t be overly concerned about the possibility that evil aliens might respond mercilessly to our messages and signals. And that argues – if it’s up to Caballero – in favor of a more active search for extraterrestrial life. Because the passive variant – in which we only listen to our ear – has, he says, little chance of success. “SETI (whereby we only try to intercept signals from intelligent extraterrestrial life, ed.) is actually looking for a needle in a haystack, given the millions of frequencies available. If we ever want to make contact with extraterrestrial life, we have to take the first step, ideally via laser communication,” says Caballero. And yes, judging by his calculations, that always carries a small risk, but if it’s up to Caballero, that shouldn’t stop us from trying to actively contact aliens. “Because risks are inherent in everything worthwhile in this life.”