What Should Humans Say To Extraterrestrials?

Humans have sent several messages into space, but don’t hold your breath for a response.
An earth-bound satellite receiver that may be used in SETI

Congratulations! You’ve been chosen as the Representative of the Human Race™ to send a message into space. You have the opportunity to blast something out into the stars with the hope that one day it’ll reach extraterrestrial intelligence. What would you say? Perhaps even more pressing, how would you make sure they understand what you say? The implications of having to communicate with something we know nothing about can bring up about a million questions. All of these questions are at the heart of a field called Active SETI.

The attempts to contact extraterrestrial intelligence have gone by a few names. First there was CETI (communication with extraterrestrial intelligence), which was eventually abandoned because communication implies it’s a two-way street. Then there’s METI (messaging extraterrestrial intelligence), which is still commonly used. And lastly, there’s Active SETI, which emphasizes that messaging is part of the overall search for extraterrestrial intelligence. 

Humans first started sending messages to space in the second half of the 20th century, and we’ve thought about it for even longer. In Extraterrestrial Languages, author Daniel Oberhaus covers the whole history of our attempts to message extraterrestrial intelligence. Again and again in these pages, the same questions arise: How can we contact extraterrestrials? What should we say? And, perhaps most importantly, should we be saying anything at all?

How Can We Contact Extraterrestrials?

It can’t be overstated how difficult it is to contact another planet. There are countless logistical issues that might make it impossible, from the difficulties of translation to the sheer vastness of space. In spite of this, humans have tried a few different methods to get our message out there.

Big, Flashy Lights

In the earliest days of interplanetary messaging, some thought that the best method would be to create some sort of massive message on planet Earth itself. Like people spelling out “HELP” in sticks on a desert isle to attract a plane, 19th-century astronomers thought that aliens would be able to read our messages. One particularly wild suggestion came from Austrian Joseph von Littrow, who thought humans could dig big trenches in the Sahara Desert, put kerosene in them, and light them on fire. Slightly less ridiculously, French astronomer Charles Cros thought that we could build massive mirrors to reflect patterns into space.

From a practical point of view, any attempt to make some big sign to aliens from Earth has no chance of working. To be fair to the astronomers mentioned, their ideas do sound more realistic when we take into account the fact that scientists in the 19th century thought there might be life on Mars or even the Moon. Now we know there’s no (intelligent) life on either, and so other methods must be used to send messages farther afield.

Launched Objects

The most obvious way for humans to send messages might be simply launching objects toward planets and star systems that show promising signs of life. So far, humans have done this twice: first with simple plaques being affixed to two Pioneer probes, and second with two golden records being placed aboard Voyager 1 and Voyager 2. All of these spacecraft, which were launched in the late 20th century, have enough velocity to leave our solar system and travel to others. Hypothetically, they could be intercepted by extraterrestrials.

While both the plaques and the records garnered media attention, they’re not very likely to actually reach aliens. For one, they were more an afterthought than the main purpose. Both the Pioneer and Voyager missions were tasked with photographing planets in our own solar system, and so they are not directed anywhere particularly promising for extraterrestrial societies. Plus, they are both moving incredibly slowly. It will take about 40,000 years for either of the Voyagers to make it to a nearby star, and hundreds of thousands more years to reach anywhere that might hold life. In the best-case scenario, aliens will find the golden records long after the end of human civilization.


By far the most promising methods in Active SETI involve radio waves and microwaves. These are both kinds of waves that exist on the light spectrum but are invisible to the human eye (the light spectrum humans can see is only a tiny fraction of all the waves that exist). Humans can send these waves out into space toward galaxies and planets that might contain civilizations capable of detecting the waves, which can be differentiated using frequencies.

There are still countless technical details that make wave communication more complicated. TV shows like the sci-fi spoofing Futurama have made jokes about the fact that technically Earth has been broadcasting itself for years; literally broadcasting, because our TV shows, radio stations and radar have all been leaking out into space for decades. But to actually see these signals, an alien civilization would need to have prohibitively large receivers, they would need to be able to differentiate between these signals and the general wave noise of space, and they would need to figure out how to turn those signals into video and audio like our human-oriented devices do. 

None of that is easy, which is why when scientists specifically want to send messages to outer space, they keep things simpler by sending out powerful beams of information in binary. That means that scientists send two different frequencies of waves in a specific order to spell things out. This is similar to how computers work: a binary system of 0s and 1s can be strung together to make more and more complicated messages. Once you settle on the method, though, you have to decide what exactly to say.

What Should We Say To Extraterrestrials?

Sending the first message to extraterrestrials is the most extreme form of “sliding into the DMs.” Everyone has different ideas on what makes the most sense to say first, and it’s all the more complicated because humans also have to say it in a way that might possibly make sense to aliens. It’s been pretty rough-going.


In 1962, the first recorded radio message was sent into space. It was directed at Venus, written in Morse code and contained the message (translated from Russian) “MIR, LENIN, USSR.” The word mir means both “peace” and “world.” It would be a shame if an alien civilization actually were to somehow receive this message, figure out morse code and somehow understand Russian, because two of the three things mentioned in that list are already gone. But chances are, this would be absolute nonsense to an extraterrestrial.

Morse code isn’t a terrible idea to start with, because like the radio messages themselves it’s based on a binary (dots and dashes). The real problem is that humans can’t take language for granted at all when they’re sending messages. Humans, according to linguist Noam Chomsky, have an innate Universal Grammar that makes language possible. And even with that advantage, there are writings that humans have never been able to decipher. Aliens don’t stand a chance.

Active SETI scientists have included some language in our messages to space. The golden records mentioned earlier have greetings in 55 languages (only a fraction of the 7,000 spoken languages of Earth). But humans will likely have to find a different method of communicating with aliens.

Math And Science

As Galileo once wrote, “The great book of nature is written in the language of mathematics.” Maybe, then, the best way to communicate with another advanced species is to communicate our common ground: the basic mathematical and scientific principles of the universe. 

One attempt to communicate through math and science was with lingua cosmica, or Lincos, which was a constructed language created by Dutch mathematician Hans Freudenthal. In his 1960 book on the subject, Freudenthal explained how Lincos could include its own instruction manual. It would start by teaching numbers first, then add in operators (like add, subtract and equal). The idea was that you could build up from these simple operations to eventually describe everything about the Earth.

Freudenthal’s Lincos was never used in an interstellar message, but it did inspire later attempts. The Cosmic Calls — two messages broadcast from a radio telescope in Crimea in 1999 and 2003 — took Lincos and adapted it. In these messages, matrices of information were created that went from explaining the numeral system to providing information about human DNA. The idea is to give some far-away civilization an idea of who we are.


Math and science are great — and there’s no irony in the fact Active SETI scientists would choose science to communicate — but what about the other ways humans express themselves? Art has been sent into space a number of times, with music being the most common option. In 2008, NASA broadcast The Beatles’ “Across the Universe” into space so that it could travel, well, across the universe, but that was more for the fun of it than a serious attempt at communication.

A few decades before the “Across the Universe” message, the Voyagers’ golden records included a playlist that featured human greetings, birdsong and some very disparate musical tracks in an attempt to capture the vast artistic range of the planet. The choice of songs meant Bach and Australian aboriginal tribes and Chuck Berry were all placed next to each other in what sounds like a very strange mixtape.

Music and art are important parts of human society, but most scientists don’t have a lot of hope that they’ll do much for human-alien interaction. It’s fun to imagine aliens rocking out to the theremin concert Russia broadcast into space in 2001, but what would another society really make of it? Humans might consider art as a universal good, but blasting it to nearby galaxies certainly puts that notion to the test.


The last common theme in the messages Active SETI has sent to outer space is location data. The plaques affixed to the Pioneer probes included maps to help alien civilizations find our solar system using nearby stars. Most messages humans have sent out have tried to tell the aliens where to direct their response. If we ever want to speak to extraterrestrials, they will of course need to find us. Do we want them to find us, though? That brings us to our third and final question.

Should We Be Saying Anything At All?

In the history of Active SETI, it’s always been controversial. From its beginnings in the early 20th century to today, loud critics have pointed out the dangers of trying to talk to extraterrestrials. Most famously, astrophysicist Stephen Hawking warned against sending messages into space. Some compare it to “shouting in the jungle.” While we might attract the attention of a benevolent society, it’s just as likely (if not more likely) that we’ll find dangerous creatures instead.

Active SETI is inextricably tied up with how humans view ourselves, because it’s impossible to avoid our own strengths and limitations. Each time scientists devise a new way of communicating with a species that might look nothing like us, we still end up with tools that mostly make sense to humans. The critiques of SETI also come from the knowledge of ourselves. We have countless examples of two societies on Earth encountering each other where one — generally the more technologically capable one — obliterates the other. Why wouldn’t we expect the same of non-human societies?

Until we get some sort of response — be it a return message or an interstellar death beam — Active SETI serves one purpose: showing humanity what it thinks about itself. Each message we’ve sent into space attempts to put our best foot forward — our scientific achievements, our artistic masterpieces — and it reveals what we would at least like to think is representative of what we humans have done. Our messages are our our online dating profile, with our favorite features highlighted and our worst entirely ignored. The whole field of Active SETI might look to an alien like a desperate, shot-in-the-dark attempt to establish any sort of connection with something, anything outside our planet. So far, we’ve encountered nothing but silence, but that won’t stop us from trying.

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