# How would an alien civilization transmit an SOS signal for other sentient beings to pick up on?

This question describes the kinds of signals sentient beings would transmit to let others know of their existence. The methods described are geared towards communicating the mere existence of intelligent life. But what if an alien civilization wanted to send an SOS signal, asking for help? What kind of message would they transmit to have the highest chance of someone hearing and understanding it?

• I'm tempted to VTC as too opinion-based, but I'm going to let it roll and see what others have to say. The problem I'm having is that how creatures express alarm is enormously species-dependent. The average human often can't tell when a bird, or a cat, or any other species is making a sound that means "I need help!" We figure it out over time and with research... but I personally can't imagine any SOS an alien race could send that would mean beans to someone who knew nothing else about the race. There's simply no context to judge the message content. Hence my worry that this is opinion-based. Jun 21 '20 at 17:22
• What sort of problem would be both so threatening that they would send such an SOS and so slow that they could expect a timely response?
– Mary
Jun 21 '20 at 22:18
• @Mary that's an interesting question, but it can be ignored as irrelevant. For example, "what happens when SETI detects its first extraterrestrial message - and it's a call for help?" The civilization may be eons dead ... but that doesn't irrationalize the question. Indeed, many questions are asked on this site without a rational background. That's OK, so long as the question can be answered without it. Though I have other issues with this question, the lack of background is not among them. Jun 21 '20 at 22:28
• @JBH Actually, it would determine a lot. For instance, if it were slow enough, you could use slower than light means to transmit it.
– Mary
Jun 21 '20 at 22:33
• @Mary All electromagnetic transmission is light and travels (in a vacuum) at the same speed. Doesn't matter if it's an FM radio broadcast, your cell phone, a laser beam, or gamma rays. So, unless you're talking about literally throwing a message jammed into a bottle.... (and the linked question is asking about radio waves and uses the word "transmit"). Jun 21 '20 at 22:37

Really, there are three parts to your question:

1. Transmitting the message
2. Translating the message
3. Translating the meaning

Number 1 is rather straightforward and there are tons of resources and other questions where you can read about sending messages at interstellar distances. Whether the signal is via radio, smoke signal, enormous flash light, or something else, making a signal receivable across interstellar distances is well within the capabilities of your standard dedicated multi-billionaire/small country today. A bigger problem would probably be that with current technology all messages would be limited to light speed and would probably end up arriving hundreds if not tens of thousands of years too late for anyone to reasonably help.

Number 2 is a bit more esoteric, but still possible in my opinion. Smarter people than I have worked at the problem of making a message decipherable to most conceivable alien intelligences. Usually, these approaches start with the understanding of a fundamental concept, such as math or elemental composition, and work upwards. I think it's reasonable to assume that through work and sufficient complexity, a language instruction system could be built which works its way up to something like English eventually.

Number 3 is a complete shot in the dark. Currently, we have no evidence of alien intelligences past or present. All we have is a couple hundred years of science-fiction writers and scientists taking their best (wild) guesses, but really, we have no clue at all what an alien might be like. Maybe, bipedal beings who navigate primarily by observing visual light are the standard, but maybe they're not. Additionally, there are meanings which may be impossible to convey to an alien mind. For example, take a core human emotion: jealousy. What if the aliens have no sense of self? No I? Yes, distress, fear, and asking for help all seem like rather fundamental animal drives and emotions, but as our sample size of "life" is one (earth), we can't really do more than speculate wildly on what aliens might be like.

If I had to do this my message would be (in English):

"Please send help, we're in trouble! Our problem is [...]"

And then I'd transmit the entirety of human knowledge (all literature, media, internet, etc) along with the message so that they can figure it out themselves.

• What's scary is that it's not unreasonable to believe the aliens would transmit their version of an SOS- or Mayday-style message. So, they're sending SOS or MAYDAY and what we're receiving is Glurk-abbadu-WHUM or Vitleble.. Vitleble... and how on earth do we figure that out? SOP isn't just species-centric, it's society-centric, too. +1 for your conclusion, though (transmit everything). Can you imagine the Contact-style argument that would ensue? "You told the brains-eating aliens what!? What do you mean they don't eat brains? Prove it!" Jun 21 '20 at 20:22
• I'm rather uncertain that any signal we can transmit from here is above the background noise for any kind of interstellar distance. In the novel "The Three-body problem" they use the Sun as amplifier precisely because the most powerful anthena we could make now would be probably too weak to be received four or five light years from here. Jun 23 '20 at 8:44
• @Rekesoft "The three body problem" is a work of fiction and in reality, sending messages over very long distances isn't that difficult. For example, we have no problem communicating with Voyager 2 which is about a light-day away only has a has a 22 watt (my smartphone charges at 25 watts for comparison) transmitter and was built half a century ago. Modern radio or laser communication can easily reach nearby stars and building it bigger is an easily accomplishable engineering task. Jun 23 '20 at 10:17
• @Dragongeek The state-of-the-art long range laser communication is going to be tested in a NASA probe set to be launched in 2022. It will be tested at ranges from 15 to 225 million kilometers. In the future it is expected to work over distances long enough to cover most of the solar system. No one expects to be workable on interstellar distances. Laser decoherence would turn any information into garbage far before the signal is too weak to be detectable. Jun 23 '20 at 11:51
• @Rekesoft Inter satellite communication is a whole different beast and has it's own host of problems. I'm talking about a transmitter here on Earth, where you could pump however much power you wanted to into a radio or laser. Even if the beam decoheres, it wouldn't really matter once you've got a couple mega or gigawatts of light blasting off into space. Jun 23 '20 at 11:58

A very long and detailed mathematical algorithm where left side should equal the right side that ends in the middle of

They'd send an SOS

It would be a short repeating pattern to get attention. Needs to be complex enough to be not natural but simple enough to be short and blasted at high power that it will get noticed.

Any alien lifeforms capable of receiving such message won't understand the language but will know someone has sent an alert because it's not background noise and it's too short to be a message.

Chaos is danger. The disruption of order by chaos is a call for help

Intelligent life must rely on patterns and pattern recognition to obtain energy in opposition to the forces of entropy. Intelligence enables pattern recognition in the service of life. Unpredictability and the failure of patterns is dangerous to life.

A sequence of prime numbers is a fine way to convey intelligence - a pattern, and one that would be recognized only by an intelligence and not produced by a natural phenomenon (as something like the Fibonacci series might).

The distress call would be disruption of the sequence of primes by random numbers, which would end the sequence. The sequence of primes would then restart at the beginning and again be disrupted and ended at a different point by random numbers: the disruption of order by chaos, anathema to life.

• I, as a human, can't decipher your proposed call for help without your explanation and the background provided to me. Still, if we assume the aliens are smarter than I, sending a series of numbers is still highly ambiguous and relies heavily on interpretation. Jun 21 '20 at 19:26
• @Dragongeek - I will write you a sonnet if you can explain a series of prime numbers using natural phenomena. Disclosure - Carl Sagans idea, not mine. I agree that disrupting a series with random numbers might be interpreted as art, or a mating call, or something other than distress. Jun 21 '20 at 19:33
• Oh, I don't disagree that prime numbers are a great way to indicate intelligence, but I don't think a series of numbers is enough to express the nuanced idea of "help". For the message to be effective, it needs to have a single, non-misinterpretable meaning Jun 21 '20 at 19:38

Show, don't tell.

It's really unlikely that any detailed explanation of a problem could be transmitted and then translated in a reasonable amount of time. So I'll just focus on sending a generic "We have trouble" signal. If you are lucky, your neighbours would decide to help and then, with a 2-way contact, it would be certainly easier to explain the exact problem.

So, what could be a likely sign of intelligent life in trouble? I'd argue that a few high-altitude nuclear explosions would send the message. Maybe reducing radio transmissions afterwards, to make it clear the explosions caused some damage. Or starting rapidly changing atmosphere composition and albedo.

Coincidentally, humanity has sent such SOS signal already.

• Please add details and a link to support your last statement. Assuming that everyone will go out and do the research to understand what you're talking about makes for a low-quality answer. Thanks. Jun 22 '20 at 4:13
• @JBH I'm sorry, the research of what? Are you saying someone may be unaware humans have used nuclear weapons? Or about rapidly increasing CO2 levels? Jun 22 '20 at 6:42
• I recognize your 2nd paragraph sets up the idea that we've sent a cry for help into space, but that's a metaphor (an artistic or philosophical belief that acting stupidly constitutes a "cry for help"). Global warming happens by both natural and industrial means, as do nuclear explosions (our own sun, for example), making both actions indistinguishable as an SOS. So, that last sentence is intrinsically false - unless you can demonstrate that humanity has sent such a message in the context of the OP's question? Jun 22 '20 at 15:56
• @JBH Wow, you are so wrong on both counts. But alright, here is an amazing research for you. Sun is nothing alike nukes (it's not even exploding), and CO2 levels never increased that fast by natural processes alone. Jun 23 '20 at 4:25
• That bought you a down vote. The OP's asking how an SOS could be interpreted if received by us. I'll happily change my down vote to an up vote if you can find any research suggesting rising CO2 (for any reason and no matter how quickly) or nuclear explosions on only a planetary scale could be (a) detected and (b) interpreted as a call for help on another planet in another solar system. Political opinions aren't facts. Jun 23 '20 at 18:02

Send a constant like Pi or e in binary at the hydrogen line, continuously for at least several days, preferably as long as possible. Use a frequency of: $$x\pi\left(1420.40575177\right)\ MHz$$

x = any natural number

This will ensure that the receiving civilization is aware of the sending civilization’s intelligence, and it cannot be a naturally generated harmonic if it is at the frequency shown above.

If the receiving civilization continues to hear the message, they will pinpoint the source of the message. They can then try to contact the civilization out of curiosity, even if they don’t know that they need help.

Regardless of language, the simplest signal would be a repeating sequence message or something whose audio interpretation consists of a mathematical pattern; a pattern that doesn't exist in nature. 1 1-2 1-2-4 1-2-4-8 1 1-2 1-2-4 1-2-4-8 or a exponential regression 1 1-3 1-3-9 1-3-9-27 A distress signal cannot be interpreted as "Distress" unless one has prior knowledge of their signals capability to be used in such fashion.

The language of mathematics

The process for sending an SOS message would be the same as the process for sending any other type of message.

Lambros D. Callimahos of the NSA wrote a technical thought-experiment paper titled "Communication with Extraterrestrial Intelligence", which has now ben declassified. You can easily find it on Google.

It explains how the message should establish a mathematical vocabulary and grammar by starting with extremely simple math equations and then increasing in complexity.

This paper quotes British mathematician Lancelot Hogben, who I think put it perfectly: "Number is the most universal concept for establishing communication between intelligent beings; therefore, mathematics forms the basis for the first steps in extraterrestrial communication."

After this, physical values (such as the constants on the periodic table) could be used to define words (e.g. for all the periodic elements).

This form of defining new words continues, using previously defined words, until you have defined all of the vocabulary you need for your message.

After this, an SOS message (or any other message) could be crafted.