What would constitute as evidence of aliens transmitting a message?

Researchers monitor radio transmissions for patterns that would support a design inference that such transmissions are sent by intelligent beings.

For example, it is claimed that it would be reasonable to infer that some intelligent extraterrestrial beings were responsible for a transmission of discrete signals and pauses that effectively enumerated the prime numbers from 2 to 101.

Now suppose we observe this transmission. Before we observe this transmission, we would, of course, not have independent evidence that intelligent life forms exist. We would also have no evidence of what their intentions would be. It is arguable that one could perhaps come up with some sort of reasonable intentions and abilities that this designer would have, but it would hinge upon the assumption that he/she exists.

Now, if one observed this pattern, most would probably conclude that there is an intelligent life form out there.

But why? Just because something is improbable by chance, doesn't mean it can't happen. One would need to show that the probability of this kind of designer existing along with it having the capabilities and incentive to send out this pattern is higher than chance.

But how can one do this independently? First, I fail to see how we can determine this. Second, I fail to see how probability even applies here. What does it even mean to ask for the probability that an alien would exist? One would have to presume that it is coming about by chance with atoms swirling around and creating intelligent life eventually, but why make this assumption?

What level of evidence would count as enough evidence for a design inference to a supernatural being instead?

  • "Now, if one observed this pattern, most would probably conclude that there is an intelligent life form out there. But why? Just because something is improbable by chance, doesn't mean it can't happen." The improbable can happen, but probably not, or it wouldn't be improbable. That's why. It goes for chance just as well as for supernatural beings, what one chooses as the working hypothesis is what's the least improbable. And what one needs to do then is not "show" capabilities and intentions, but try to confirm it, by further observations, attempts to communicate, etc.
    – Conifold
    Dec 30, 2022 at 14:22
  • I'm no expert, but I'm assuming we don't have any evidence of non-human animals producing the "transmission of discrete signals and pauses that effectively enumerated the prime numbers from 2 to 101". This presumably leads to us reasonably concluding that were we to receive such communication that it were coming from a being of roughly our level of intelligence or greater. Dec 30, 2022 at 14:31
  • Well, this is as good a time as any to bring up the topic of natural vs. unnatural. Ab initio I was under the impression that a radio signal consisting of (a sequence) of prime numbers would be highly unusual i.e. it would make my antennae go up. However, prime numbers are as natural as the Fibonacci sequence you see in nautilus shells and sunflowers - cicadas have a life cycle of a prime number of years (allegedly to avoid predation as their cycle will coincide with fewer other life cycles). So yeah. Dec 30, 2022 at 15:36
  • @Futilitarian. Again, I don't see how that follows. No matter how improbable something is by chance, it is possible. One would have to independently show that it is even POSSIBLE for another non human being, somewhere out there, to send out that message? And in order to do this, you would have to independently show that it a) exists, b) has the right motivations, and c) has the capabilities. Have we EVER come across a design reference where we didn't already have demonstrated a), b), and c)? Dec 30, 2022 at 16:42
  • We have a cognitive bias for inferring intentionality, at least according to naturalized and evolutionary epistemologies. Start here plato.stanford.edu/entries/epistemology-evolutionary and here plato.stanford.edu/entries/collective-intentionality Justification would occur for such thinkers according to contemporary scientific standards of various disciplines. More broadly, the argument would be subject to philosophy of mind. What constitutes an artifact of a mind? iep.utm.edu/theomind
    – J D
    Dec 30, 2022 at 20:37

6 Answers 6


Why do you suppose there is a simple threshold for determining whether a signal from outer space has been generated by intelligent life? In reality, if a borderline signal were received it would generate enormous interest and debate, with some parties arguing vociferously that it proved the existence of alien life and others looking for other interpretations. Without making further assumptions about the nature of the signal- was it a one-off, was it repeated, what exactly was the nature of the encoding, what did the encoded information seem to mean- it is hard to say what the consensus about the message might be. My guess is that if we could not postulate how the message could have come about by chance, then we would take it as suggesting that intelligent life might exist elsewhere, but we would maintain an open mind about it.

  • And then we would go about formulating more theories to validate with more data, try to bracket that new thing from different angles, ... The media would be all over it with a storm of "aliens exist!" though :-)
    – Frank
    Dec 30, 2022 at 16:39

As always, keep data at top, theories below.

At one pan of a balance there is no evidence at all of such transmission happening naturally, and not for lack of data; at other pan of balance is all random noise nature generates all the time.

Which side will the balance tilt?

Having rule out natural phenomena what else is there? Us. Once we are sure its not humans that made this transmission the only logical conclusion is, it must be non-human intelligent life.

Ofcourse one such datum is not enough for conclusion. As you said it may be a rare but totally natural signal.

If more such transmission are received the case for natural phenomena get weakened simply because of extremely low probability.

Still, we can never be sure till we actually see an alien making that transmission. Its just that its not a logical path to follow to wait for an actual encounter before drawing conclusions from available data.


Hmm. You seem to be thinking of deductive reasoning, with straightforward rules, and no judgement in applying them. Empiricism is not like that. Empiricism does not work with "simple thresholds", but with judgement calls. What constitutes evidence, the strength of a piece of evidence, etc., all are judgements. When there is a claim of evidence for something new, the peers of the claimant examine the evidence themselves, consider alternate explanations, and make predictions about what ELSE we could reasonably suspect if the claim were true, then look for that too. Support for a claim is a cumulation of evidences, and the claim is a reasonable inference to the best explanation. Note that most of what we postulate in physics, we do not actually directly observe. Energy, entropy, quarks, etc. -- all are not DIRECTLY observed, they are all unobserved inferences to best explanation.

For ALL empiricism, there is always the possibility that our inference is wrong. We can use probabilities of a prime number series NOT being random by comparing to observations of other stars, and the signal patters we see from them, which appear to be mostly random white noise. But white noise can produce patterns on occasion by chance, so that is always a possibility. That is why SETI does not just look for one thing, but a variety of possible patterns, and the possibility of then interpreting other signal patterns, and extracting more possible information out of background noise. If THAT works, and we find there are messages PLUS the primes, then the "random vs communication" debate would end up settled pretty quickly.

SETI provides a good reference for thinking about trying to evaluate evidence for a "supernatural" designer. To infer design, one first has to postulate a character, and intentions, to an agent. Then look for possible consequences from those inferences. AND the design hypothesis has to be the "best" explanation, in that it knits more evidence in a coherent story, AND makes useful and testable predictions.

I also suggest you drop the use of "supernatural" here. The two most common usages "about Gods or spirits" and "not within the realm of evaluation thru empiricism or reasoning" are often equivocated. You want to DO "methodological naturalism" on a spirit hypothesis, and calling the hypothesis "supernatural" would put it outside that possibility per the second definition. Better terms would be "discarnate agency" or "spiritual designer", because they would help people plus yourself to avoid the equivocation fallacy while thinking about the hypothesis.

Back to evidences. Note I said we need to make assumptions about a designer. IF one postulates the Biblical God, then there are a LOT of "characters" and "intentions" one would expect based on claims and descriptions in that reference about that God, and LOTS of test cases one can look for, in addition to possible traces of design in the universe. What has happened for most scientists, is that there are enough failed predictions form those inferences, that the vast majority of scientists consider the Biblical God to not be a useful or best explanation for our universe -- and for that hypothesis to be effectively refuted.

However, this is not the end of the story. ALL hypotheses are infinitely klugable, with the possibility of special case assumptions added to explain away apparently contrary evidence. The scientists who DO believe in a Biblical God, have to make a lot of special-purpose assumptions to counter the falsified predictions from the Bible. For the literalists, this induces reasons to reject lots of scientific consensus in multiple fields. For the non-literalists, this includes accepting that the Bible is reinterpretable in very non-intuitive ways -- such that its character descriptions are not useful for making testable predictions. This makes the Biblical God NOT the "best explanation" for most testable features of our universe.

The issues that a Biblical God hypothesis encounters, are even more informative than the SETI experiment in evaluating discarnate designer hypotheses. If one postulates a designer of our universe, one must postulate SOME kind of purpose: Life, Beauty, Uniqueness, or SOMETHING, in order to have an intention to test for and provide predictive explanations. We can test our universe for uniqueness -- and the commonality of materials, of galactic structure, and of star structure, repeated billions or quadrillions of times, is NOT consistent with a uniqueness intention. Same with beauty. There are SOME aspects of our universe that are beautiful, but many more which are not.

Life seems to be the most useful of design intentions, and that was the one widely held, until the process of evolution was discovered, and that provided a better "best explanation" for the structures and effectiveness of living things. Design would predict life to appear fully formed, and optimized -- but life appeared late in our universe, and at first very simple. And while life tends to be optimized, it is a peculiar optimization with major design flaws embedded -- like the human lack of vitamin C production, and our hanging our organs off our spine not our rib cage, which make a lot more sense evolutionarily. Our ancestors lived off a diet of fruits, and did not need the vitamin C self-production that most critters have, so losing the ability to make our own vitamin C was not a problem for them. And organs hung off a spine is fine for the four legged creatures that we evolved from. There are multitudes of these features of life that are far better explained by a gradual evolutionary process, where later optimizations have to adapt around architecture choices made for different environments for ancestor species. A pure design process should in contrast have everything optimized without these sorts of poor architecture features, and the ability to explain these non-optimizations strongly supports evolution over design.

A universe designed FOR life is still a possibility. Our understanding of physics is that the constants of the Standard Model are contingent aspects of our universe -- they could have been almost anything. BUT -- when we run what-if physics models, almost the entire range of possible values for most of them would prohibit a universe with life. The universe would exist only for an instant, or blow apart and have effectively zero density and no interactions, or all the mass would end up in black holes, etc. So -- if the possible range of constants is what we think it is, the odds of a universe being able to support life is astronomically small. This thesis is called the Fine Tuning hypothesis. and while astronomers and physicists initially resisted it, it has now been mostly accepted as a reasonable interpretation of the Standard Model. However, an alternative to Fine Tuning has been identified, and that is Apparent Fine Tuning, in which multitudes of universes are created (the multiverse hypothesis), and all life would then find itself in one of the rare "Apparently Fine Tuned" universes, thru an Anthropic Principle.

There is currently no evidence for multiverses, so if a Deist life-intending creator hypothesis could produce some other useful predictions, that could be a possibly more useful prediction than a multiverse. Deism is not strong on predictions, so that aspect of a design/creation model is hard to make useful. The potentially more productive area to look for predictive power is thru looking for other ways that spirit/discarnates might interact with our world. The work of the parapsychology association to look for psi phenomenon https://parapsych.org/articles/36/55/what_is_the_stateoftheevidence.aspx, combined with the failure of physicalism to answer the hard problem of consciousness, provide some support for the possible plausibility of a Deist design origin to our universe.


The thought experiment you suggest requires a few more assumptions, but if we simplify it to mean "what is the probability of detecting the first 26 primes in order among all possible strings of random numbers between 1 and 101?", then the maths comes out as: 1/101^26 = 7.72e^-53, which probably blows out of the water any 6 sigma significance threshold we use in physics to argue for "discovery". If the pattern repeated, that would further reinforce the "discovery". Physicists would conclude that H0 = "this is random" is not supported by evidence.

The words are important here. Nobody says "aliens exist". Physicists would just say "the evidence does not support that this event is random". But this is what real science claims look like.

  • hear hear. Very well put.. Dec 30, 2022 at 16:35
  • Have we ever inferred if a sequence is not random PURELY because of its low probability? I would argue that in each case we determined this, we had evidence that a "non random process creator" exists apriori. Every time we have came across a pattern, it was either determined to be non intentionally designed in the case of nature, or intentionally designed. But in each case of intentional design, it was always some process created by a human. But in ALL of these cases, we had independent evidence that these humans exist and that they also have incentives/abilities to carry out that process Dec 30, 2022 at 16:39
  • @thinkingman Please look at my reply again. Physicists have no use for "intention", and are very parsimonious with the reach of their claims, on purpose. The way modern science carefully formulates its claims is the result of a very long intellectual history, very cognizant of all the pitfalls of induction. Claims are calibrated to obviate debates like the one we are having, which are not conducive to making scientific progress.
    – Frank
    Dec 30, 2022 at 16:46
  • @thinkingman I understand it doesn't sit very well with most people, who would prefer ready-made certainties like "we conclude therefore that XYZ exists", but however uncomfortable it is, it's real scientific life.
    – Frank
    Dec 30, 2022 at 16:50
  • It really depends on what you mean by random. If by random, you mean a non uniform distribution, then yes, you can conclude that it is not one, just by the data, only if you have enough of a sample set. But you cannot conclude that a particular series of data came about INTENTIONALLY just from a low probability Dec 30, 2022 at 16:59

“If there is a Creator, he must have an inordinate fondness for beetles” -J.B.S. Haldane (1892-1964)

Various tactics can be used towards parameters for how likely life is. We know it happened once, we think we know it started at a White Smoker, where conditions allowed cell-membrane-like conditions & RNA soup to occur, that require specific materials. We think life hasn't spread in the solar system yet, or spontenously occurred on Venus Io or other candidate celestial bodies. We can look at the atmosphere of anincreasing range of Earth-like planers for traces of oxygen, phosphine, and other reactive gases that would indicate life. We can also look at whether there are hard steps or a great filter/s, and consider odds for candidates.

Odds of something happening by chance are contextual, but in scientific work like particle physics there is a clear parameter, six sigma unlikeliness it happened bty chance. Discussed here: How improbable does an event have to be before we can say it didn't happen by chance? We know from the Dunbar Number that our neocortex evolved primarily to navigate our social environment and work out intentions of others, which we can relate to how we describe Causality, and draw inferences from experiences Is the idea of a causal chain physical (or even scientific)? Likelihood is crucial to our making sense of the world - but it absolutely can be questioned, like as framed by Hume's Problem of Induction. We finding bridges between the rigorous models of physics, & the macroscale, as discussed here: Is the idea that "Everything is energy" even coherent?

We can't even speak with dolphins yet, which have very similar biology to us and are right here with us. Spacefaring aliens would likely be so far beyond our thinking that we would be like barely sentient animals to them, and similarly with our own descendents a million years from now, a cosmic blink-of-the-eye. We wouldn't be communicating, we would be getting signals, and being sure they didn't happen by chance.

Unless the 'Dark Forest' Great Filter scenario is the solution to the Fermi Paradox.


How does one make a design inference for a designer not discovered yet?

On questions such as these, I think that Alan Turing got it right in 1950 when he described the imitation game, now better known as the Turing Test: if a human reader cannot tell whether a written communication is from a person or a machine, then the source of the communication is something that can think.

Turing was answering the question, "Can machines think?" In the example posted by thinkingman, the terrestrial observers would not know whether something alive sent the message or whether it was sent by machine. However, they could reasonably conclude that the message was sent by something that can think; and that is all they would need to know.

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