Suppose we detect a signal and want to reply, or suppose we receive a message and want to understand it. A reasonable person might assume that’s the easy part — the hard part being detection. It’s the reverse. Communicating with an alien civilization may be one of the hardest problems imaginable, and the obstacles aren’t mainly about technology. They’re about distance, language, and the absence of anything shared to build on.

The Conversation-Killing Distance

Start with the most unforgiving barrier: the speed of light. Even our nearest neighboring stars are several light-years away, and any civilization we detect is likely far more distant — dozens or hundreds of light-years. A signal takes that many years to travel each way.

This makes conversation, in any normal sense, impossible. Send a message to a civilization a hundred light-years away, and the reply, if any, arrives two hundred years later. The person who sent the message would be long dead before an answer came. “Communication” across interstellar space isn’t a dialogue; it’s a series of one-way transmissions separated by spans longer than human lifetimes, possibly longer than civilizations. Whatever we send, we send to a future we won’t see, and whatever we receive may come from a sender who no longer exists.

No Shared Anything

Set aside the distance and an even deeper problem remains: we’d have no shared language, no shared history, no shared biology, no shared frame of reference of any kind. Every human language, however foreign, was created by humans with human bodies, senses, and experiences. An alien civilization would share none of that.

Human translators rely on common ground — pointing at objects, shared physical experience, related languages, historical contact. With an alien sender, all of that is gone. We couldn’t point. We might not perceive the world through the same senses. Concepts we consider basic might have no counterpart for them, and vice versa. Even decoding the structure of an alien message — figuring out what counts as a symbol, where one unit ends and another begins — could be a formidable challenge before any question of meaning arises.

The Math Bet

The standard proposed solution is to fall back on what might be genuinely universal: mathematics and the laws of physics. The idea is that any technological civilization must have discovered the same mathematics — prime numbers, the value of pi, the structure of arithmetic — and the same physical constants. These could serve as a shared starting vocabulary, a foundation both sides recognize.

In 1960, the mathematician Hans Freudenthal designed exactly such a system: a language called Lincos, built from mathematical and logical principles, intended to be understandable by any sufficiently advanced mind from first principles. The approach is elegant: start with simple arithmetic both sides can verify, then gradually build up to more complex concepts using that established common ground.

The bet is plausible but unproven. We assume mathematics is universal, but we’ve never tested that assumption against a genuinely independent intelligence. An alien mind might formalize mathematics so differently that even prime numbers aren’t an obvious bridge. We simply don’t know, and we have no way to find out until we try.

The Decipherment Warning From Home

There’s a sobering reality check available right here on Earth. Human beings have created scripts that other human beings, with shared biology and sometimes even known historical context, still cannot read. Several ancient writing systems remain undeciphered despite decades of expert effort. We struggle to read messages left by our own species a few thousand years ago.

If we can’t reliably decipher human scripts — produced by people with brains identical to ours — the difficulty of decoding a message from a wholly alien intelligence comes into stark relief. The decipherment problem is hard even under the best possible conditions. With an alien sender, the conditions would be the worst imaginable.

The One-Way Nature of It All

Put these together and “communication” with extraterrestrial intelligence starts to look very different from the conversations of fiction. It would most likely be the transmission and reception of self-contained messages, each designed to be understood without any back-and-forth, each crossing spans of time that dwarf human institutions. The sender builds a message hoping it’s decipherable; the receiver, perhaps centuries later, tries to crack it cold, with no chance to ask a clarifying question.

This is why so much thought has gone into how to construct a message that could stand alone — readable without context, built up logically from universal foundations. It’s the interstellar equivalent of writing a letter that must be understood by someone who shares none of your assumptions and can never write back.

Why It’s Worth the Difficulty

Given all this, one might ask whether communication is even possible. The honest answer is that we don’t know — and won’t, until there’s an actual signal to work with. The barriers are real and severe: the distance that forbids dialogue, the absence of shared reference, the unproven assumption that mathematics bridges all minds, the humbling difficulty of decipherment even among humans.

Yet the potential reward is so vast that the effort continues. A single decipherable message from another civilization could carry knowledge accumulated over a history far longer than ours. Even understanding a fragment would be among the greatest achievements imaginable. So researchers keep designing universal languages and refining transmission strategies — preparing, against long odds, for a conversation that may never come, but that would change everything if it did.

Designing a Message That Teaches Itself

If we can’t rely on shared language, any message we send has to be self-teaching — built to be understood by a mind that starts with nothing in common with us. This is the opposite of cryptography. Where a code is designed to hide meaning, an interstellar message must be “anti-cryptographic,” engineered to make its meaning as easy to extract as possible from first principles.

The usual strategy is to start with what should be universal and build upward. Begin by establishing simple counting and arithmetic, which any technological civilization should recognize. Use that established foundation to define symbols, then use those symbols to describe physical constants, then chemistry, then perhaps biology and a description of ourselves. The 1974 Arecibo message attempted a crude version of this, arranging 1,679 bits — the product of two prime numbers — into a grid that, decoded correctly, sketched our number system, DNA, and the human form. Whether such a message could actually be understood by genuinely alien minds is unproven, but the design philosophy is sound: assume no shared context, anchor everything in mathematics and physics, and let the message bootstrap its own interpretation. It’s the hardest writing problem imaginable — composing for a reader who shares none of your assumptions.

The Time-Capsule Alternative

There’s a completely different approach to reaching other minds, one that sidesteps radio entirely: send a physical object. The Pioneer plaques and the Voyager Golden Records are exactly this — durable artifacts carrying messages by hand into interstellar space. The trade-offs are stark and instructive. A physical record can be far richer than a radio transmission, carrying images, sounds, and detailed information on a medium designed to survive hundreds of millions of years. The Voyager records will outlast not just our broadcasts but very likely our civilization.

The catch is reach. These objects move at a tiny fraction of light speed and aren’t aimed at any particular star; the odds of one ever being found are vanishingly small. A radio message crosses light-years in years; a physical probe takes tens of thousands of years to travel the same distance. So the two strategies trade speed and reach against richness and permanence. Radio can reach far, fast, but fades and must be decoded cold. A physical artifact carries a fuller message that endures almost indefinitely but may drift forever unread. Neither solves the fundamental problem of communicating across the gulf — they just fail in different, illuminating ways.

Preparing for a Conversation That May Never Come

Given barriers this severe, it’s reasonable to ask why anyone works on interstellar communication at all. The answer is that the groundwork has value regardless of whether a signal ever arrives. Designing self-teaching messages forces us to ask what is truly universal about knowledge. Wrestling with decipherment sharpens our understanding of language and meaning. And should a real signal ever come, the difference between having thought these problems through and starting from scratch could be enormous. Researchers prepare for a conversation that may never happen because the cost of preparing is small, the reward of being ready is vast, and the act of thinking it through teaches us a surprising amount about ourselves.

SETIworld follows the deep problem of talking across the stars — distance, decipherment, and the search for a common language. Join the portal to track the science.

References

• Freudenthal, H., Lincos: Design of a Language for Cosmic Intercourse, North-Holland 1960
• Vakoch, D. (ed.), Archaeology, Anthropology, and Interstellar Communication, NASA 2014
• Oberhaus, D., Extraterrestrial Languages, MIT Press 2019
• DeVito, C., Science, SETI, and Mathematics, Berghahn 2014
• McConnell, B., Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations, O’Reilly 2001
• Atri, DeMarines & Haqq-Misra, A protocol for messaging to extraterrestrial intelligence, Space Policy 2011