Imagine that you’re a member of an advanced extraterrestrial civilisation and you want to broadcast your presence to the rest of the galaxy. Perhaps you want to transmit a detailed philosophical treatise to other intelligent life forms or maybe you just want to shout out “Hello Universe”. How would you go about doing it?
The honest answer is that we just don’t know. Our mechanisms for thinking have been influenced by ages of Earthbound biological and cultural evolution. Intelligent extraterrestrials (if such beings exist) will have a quite different evolutionary heritage and, presumably, they’ll think in quite different ways. It’s presumptuous to suppose we know how extraterrestrials would approach the problem of interstellar communication.
Nevertheless, we can make some attempt at answering the question. For example, humans and extraterrestrials (if they exist) must have some things in common: we live in the same universe and presumably are subject to the same laws of physics. Those factors in turn would surely influence any attempts at interstellar communication. For instance, we can plausibly argue that an extraterrestrial civilization would employ radio waves to transmit their message (since radio waves are cheap to produce, travel at the fastest possible speed, and at certain frequencies they are less likely to be absorbed by interstellar material than many other electromagnetic wavelengths). In the vast spectrum of radio frequencies, the region between 1.42 GHz (the hydrogen, H, line) and 1.64 GHz (the hydroxyl, OH, line) looks like a particularly promising place at which to broadcast: the region is naturally quiet and the combination of H and OH makes H2O – and water, so far as we know, is necessary for life. (So if we assume that they know that we know that they know that water is important, then this waterhole region may be the place at which civilisations gather.) It would make sense to send a narrowband signal (since it’s easy to make a really bright narrowband signal; furthermore, nature tends to generate wideband emissions, so a narrowband signal stands out as being artificially generated). And so on and so on. Arguments such as these have motivated those interested in the search for extraterrestrial intelligence to employ radio telescopes in their quest.
But let’s return briefly to our alien broadcaster. You’ve decided to broadcast a radio signal (for the reasons given above), but how to maximise your chance of some other civilisation receiving the signal? Well, the best way of doing that would be to broadcast isotropically, in all directions, continuously. Fine, but that’s going to be very expensive. To cut costs you might choose to transmit isotropically but only in bursts (perhaps one second in 100,000). Or you might transmit a highly directional beam towards one star before moving it on to another star, and not return to any particular star for quite some time.
Suppose an alien civilisation followed the logic outlined above. What would we see? Well, if a radio receiver happened to detect the signal then it would undoubtedly capture our attention. But the signal would soon be gone – either because the transmitter was down or because the transmission had moved on to some other star. We wouldn’t know for sure whether we’d heard from another civilisation.
Can you imagine how frustrating that would be?
Well, that’s the situation in which we find ourselves. On the night of 15 August 1977 the Ohio State University Radio Observatory – “Big Ear” – was pointing 20 degrees above the southern horizon. Just after 23:15 one of the telescope’s two feed horns began to register a signal. Over the next 30 seconds the signal reached a very strong peak and then, as the Earth rotated, the signal faded.
No one was present when the telescope registered the signal. The setup was such that a printer clattered out a line of characters, one every 12 seconds, with the characters reflecting intensity. It was only later that Jerry Ehman checked through the wads of computer printout. When he saw a pattern in the printout – 6, E, Q, U, J, 5 – he circled it and scribbled “Wow!” beside it. Ehman knew precisely what an interstellar radio transmission was supposed to look like – and it looked like this. It had the same signature as a celestial source passing through the telescope’s antenna beam, but the only natural radio sources in the beam were a thousand times fainter than the Wow. It had a narrow bandwidth. The frequency was close to the hydrogen line. Most intriguingly of all there were hints (if you really looked for them and then cast a favourable eye) that there was some sort of pattern involved with weaker signals. The Wow remains perhaps our best candidate for a signal from an extraterrestrial civilization. The trouble was, the Ohio State radio telescope looked for the signal again and in about a hundred days of additional observations it saw – nothing. Admittedly, that additional observing time added up to only four hours. The astronomers involved could justifiably have spent a longer time looking for the signal. (Longer observations would be particularly appropriate if extraterrestrial civilisations were employing a “lighthouse” approach to broadcasting: if we were in the line of fire then the rotating beam would periodically sweep across our view. Long listening times could pick up this periodicity.) On the other hand, the telescope was there to do astronomy not to search for extraterrestrial intelligence. The astronomers involved wrote up their observations and moved on to other things.
The printout showing Jerry Ehman's 'Wow' annotation next to a signal recorded by the Big Ear observatory. The characters relate to signal intensity, with the letter 'U' representing a 30-sigma peak.
(Credit: Ohio State University Radio Observatory/NAAPO)
Enter urban planner and data analyst Robert H. Gray.
In his book The Elusive Wow: Searching for Extraterrestrial Intelligence, Bob Gray describes his remarkable attempt to track down the source of the Wow signal. The word ‘remarkable’ is appropriate here because Gray was an outsider (no astronomy PhD, no funding, no institution) who managed to get time on a Tasmanian radio telescope, a Harvard receiver, and even the Very Large Array in order to continue the search for the Wow signal. He also built his own automated microwave observatory to use in the search. (I’d like to know what his neighbours thought when they saw him rolling a 12-foot ex-military dish antenna through the narrow Chicago alleyways near his home.) Gray managed to do all this partly, I’m sure, through judicious application of a persuasive personality; but mainly because at all times he presented strong, well-reasoned, science-based arguments for searching for the Wow signal. His analysis of the data generated by his observing time on various telescopes was clearly of professional standard. So although Gray was an ‘amateur’ astronomer, he was an ‘amateur’ in the best, old-fashioned sense of the term.
The Elusive Wow is really two different books. The first part describes Gray’s personal relationship with the Wow signal. The story is told with clarity and humour, and along the way the reader learns a lot about how astronomy is actually done. The second part, which is much more traditional, presents an overview of the search for extraterrestrial intelligence – it gives the rationale behind, and the history of, SETI. For the newcomer to SETI, it might be advisable to read the second part first; a SETI veteran, I suspect, would skim the second part. There’s also an extensive bibliography, some useful links, and a photogallery of some SETI luminaries.
Even if you are an expert in SETI folklore you will enjoy part one of the book. In his approach to solving the Wow mystery Bob Gray bears an uncanny resemblance to Detective Columbo – he’s always asking “one more thing”. The difference is that Gray’s quarry is not a criminal but nature herself. Where did this extraordinary tenacity come from? Well, Gray relates a story told by his graduate school statistics professor, a story that clearly influenced him. In the early days of gasoline engines a researcher noticed a measurement in some gas samples that implied an implausibly good batch. Rather than ignoring the outlier as a fluke, the researcher tracked the path along which the gasoline had been shipped. He wanted an explanation, and he found it: the material had been contaminated in transit. The contaminant eventually became a valuable fuel additive that made engines run better. The moral was clear: if you are willing to hunt down the cause of a mysterious measurement then you might can something big. Nothing is more mysterious than a possible signal from extraterrestrial intelligence. Nothing could be bigger than confirmation of their existence.
Did Gray succeed in tracking down the Wow signal? Nope. Despite all the detective work, this is one case where the culprit got the better of Columbo.
The Wow signal might have come from a distant extraterrestrial source. But my bet? I think it was probably manmade interference of some sort, but that we’ll never know for sure.
Frustrating, or what?