Andrew Masterson
Andrew Masterson is a former editor of Cosmos.
Concluding that the search for intelligent life in the universe, known as SETI, has failed is not supported by current evidence, according to a trio of astrophysicists from the Pennsylvania State University in the US.
In a paper lodged on the Cornell University pre-print platform, ArXiv, Jason Wright, Shubham Kanodia and Emily Lubar set out to put the current failure of SETI programs into a mathematically rigorous context.
They do so, imaginatively enough, by testing a 2010 metaphor framed by US astronomer Jill Tarter, who, with colleagues, wrote that to date SETI searches had covered so little of the observable universe that to pronounce the exercise a failure was the equivalent of “having searched a drinking glass’s worth of seawater for evidence of fish in all of Earth’s oceans”.
Wright and his colleagues test Tarter’s implied parameters by constructing an nine-dimensional model of SETI boundaries. They conclude that her metaphor is an exaggeration – but not by much.
Their model suggests that the true extent of completed SETI searches is “similar to the ratio of the volume of a large hot tub or small swimming pool to that of the Earth’s oceans”.{%recommended 7643%}
The basis for the search for extra-terrestrial life – formalised by the US-based SETI Institute since its formation in 1984 – is pretty straightforward. Using data obtained from radio-telescopes, satellites and probes, its scientists look for “technosignatures” that might represent deliberate signals beamed out by technologically advanced (or, at least, competent) aliens.
So far, notwithstanding the occasional moment of surprise and hope, the results, after due review, have been uniformly bupkis.
This somewhat disappointing outcome has resulted in responses that can be characterised as pessimistic, pragmatic, or ingenious.
In a paper earlier in 2018, researchers from the Future of Humanity Institute at Oxford University in the UK modelled the outcome of combining two SETI fundamentals: the Drake equation, which calculates the likelihood of ET existing, and the Fermi Paradox, which states that if ET does exist then it’s very weird that we haven’t encountered it yet.
The results of the modelling were pretty depressing, at least for ET hopefuls. “We find a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe,” the scientists concluded.
The statement echoes that of Massachusetts Institute of Technology cosmologist Max Tegmark, who wrote in 2010: “My personal guess is that we’re the only life form in our entire observable universe that has advanced to the point of building telescopes.”
Wright and colleagues also cite a different approach to the issue, arguably best argued by Arizona State University physicist – and Cosmos columnist – Paul Davies, in his 2011 book, The Eerie Silence.
In it, Davies suggest that SETI searches need to be recalibrated, proceeding along less anthropocentric lines. ET signals may not be readily distinguishable from “natural” ones, he says, and explores other possible routes of communication, ranging from quantum computing to using viruses as vehicles for DNA-encoded information.
All of which is probably fine and valuable, but the Penn State scientists say that abandoning conventional SETI – or assuming the results to date are conclusive – is very premature.
“Despite the passage of nearly 60 years since the first radio SETI searches, very little actual searching has been done compared to the amount needed to rule out the presence of even a large number of ‘loud’ beacons,” they write.
This, of course, is because space is – to quote the late Douglas Adams – big, really big. It’s so big, of course, that even the search for startlingly obvious, blatant SETI signals has covered barely any distance.
And that’s important. Wright and colleagues place the search for technologically adept ET into a broader context of the search for anything not immediately obvious (they use the hunt for neutrinos as an example).
“Searches for first examples of hypothesised physical phenomena proceed through a series of progressively stringent null results,” they note.
In other words, the first stage of any search strategy will look only for the extremely obvious. When it fails to find it, that doesn’t mean the phenomena don’t exist – just that researchers have achieved “a new upper limit that future experiments can improve upon”.
Current SETI searches, Wright and colleagues say, haven’t even got that far yet.
“Calculating search completeness requires defining the boundaries of the search; in many cases one can always look harder for ever rarer or more subtle or more extreme events,” they note.
“The huge range of potential technosignatures also means that one survey cannot hope to be sensitive to all of them, requiring searchers to hypothesise a particular form of signature that they can put interesting limits on with their survey.”
To try to quantify that process, the researchers construct a nine-dimensional model aimed at refining SETI strategies and targets.
The hunt for ET has often been compared to looking for a needle in a haystack. Wright and colleagues develop the metaphor, and claim their approach will enable researchers to better calculate the total number of haystacks in play, the size and number of needles hidden in each, and aid in distinguishing between a real needle and just an unusually needle-like bit of straw.
The dimensions they use for their model are: sensitivity to transmitted or received power; transmission frequency; distance and position (involving three dimensions); transmission bandwidth, time and repetition rate, polarisation; and modulation.
The result, they say, is an approach that can “rigorously define” both the size of any given galactic haystack, and the fraction of it that needs to be searched for needles. And the main result that jumps out, the researchers say, is that “our current search completeness is extremely low”.
Making this finding well known, they caution, might precipitate a public relations disaster “by suggesting that the SETI haystack is so large that we can never hope to find a needle”.
This would be an unnecessary conclusion, they say, because “the whole haystack need only be searched if one needs to prove that there are zero needles”.
The aim of SETI, they continue, has never been to find all intelligent life beyond Earth. Just a single example will be ample.
“Because technological life might spread through the Galaxy, or because technological species might arise independently in many places, we might expect there to be a great number of needles to be found,” they conclude.
