The problem with that ‘blue sky thinking’ we were introduced to by New Labour is that we happen to perceive the sky as blue only because of our particular physiology and arrangement of senses on this particular planet. ‘Blue sky thinking’ doesn’t so much encourage limitless imagination as embed in its own metaphor our absolute inability to think outside our perceptual and conceptual limitations. We can’t help but do it our way. We get a poor enough result when we use ‘blue sky thinking’ to figure out innovative ways to deal with economic or social problems, and do no better contemplating the possibility of life elsewhere in the universe. We think of aliens and immediately cut them down or up (or some other inconceivable dimension) to our size. They can be bigger or smaller, their heads huge, their eyes bulbous; they are usually humanoid, occasionally reptilian, but they are always recognisable as variations on the theme of life on planet earth. This is as true when we set out to imagine alien behaviour as it is when we imagine their shape.

In 1967, astronomers in Cambridge listening to deep space with their new radio telescope heard signals pulsing at precise and regular intervals. One possible explanation they came up with was that they had tapped into an invitation to say hello sent out by intelligent beings from another galaxy. Martin Ryle, the future astronomer royal, was in charge of the group. His response was unambiguous: if they had really found extra-terrestrials they should immediately dismantle the new telescope and not tell a soul about the signals, on the grounds that they wouldn’t be able to resist replying and alerting the possibly hostile aliens to our existence in this cosy, uninvaded corner of the universe. In fact, they had discovered pulsars. Stephen Hawking agrees: ‘If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans.’

When the truth seems to be out there, our best bet for surviving would appear to be not to let a pin drop while circling our wagons. They might be peaceable seekers after companionship in the universe, but they might not be, and far safer to overestimate ETs’ aggressive tendencies than risk inviting Wellsian Martians or Wyndham’s triffids to do their worst. We are star stuff, and if star stuff is anything like us, it would be wise to reason, we should be very wary indeed. Ryle and Hawking aren’t the only ones who suppose that if they’re beeping us, there’s something they want, and if there’s something they want and we have it, they’ll certainly come and get it. Better to err on the side of planet survival and assume that they are greatly in advance of us technologically, and hostile. After all, they’ve been sending out radio feelers for millennia and we only got our radio telescope the other day. In relation to aliens, we invariably consider ourselves to be the junior thinkers and makers, though often we imagine we are nicer. But they are so much older and more savvy that in all likelihood they’ve used up their own planet’s resources and are looking around the universe for a handy new planet to inhabit. Ours, we think, would be just dandy for the kinds of alien we imagine. So answer them and chances are they’ll be enslaving us or harvesting us for food, interbreeding with, or genetically modifying us so that our children are born with uncanny blue eyes and an emotionless stare that turns all human hearts to stone.

That is one standard story of human contact with extra-terrestrials. Another view is that they have been watching us, even walking among us, for millennia. Quietly waiting for us to outgrow our reptilian, mammalian and higher primate incarnations until our poor homo sapiens brain finally fangled the right telescope to hear their signals. Like wise parents, or paternalist gods, they are giving us our head in adolescence and will be on hand to teach us what we really need to know about the meaning of life and the universe when we are ready (see Arthur C. Clarke and Stanley Kubrick). Or – another benevolent scenario – they are like those concerned parents who would, we’ve been told, have prevented the recent earthly riots. They have already stepped in, alarmed at the way earthling civilisation is going and have been taking steps to prevent us blowing ourselves up or indulging ourselves to pieces. The free-will thing may have prevented us from growing as wise as we could be, but imagine what the planet would be like without their surreptitious interventions.

Aliens have nothing but contempt for us, or they love us. Oddly, they don’t seem to be indifferent to us (how could anyone be?), though this is surely the best explanation for the apparent absence of signals, given – so the calculations go – that there are at least ten billion planets in the universe capable of producing intelligent life. Even this bit of arithmetic may be based on our incapacity to think beyond ourselves. A recent paper I don’t pretend to understand uses ‘a Bayesian analysis of the probability of abiogenesis’ to show that life might, after all, be very rare; rather lax mathematical assumptions about the term ‘likelihood’ caused the error in the old equation. It’s all maths to me, but I think this relates to the fact that the terms used for the way life might come about are based on the sole example we know of universal life, which is us and our fellow creatures on this planet.

Try as we might to imagine ETs that are not like us, we remain the baseline. In The Myth and Mystery of UFOs, Thomas Bullard suggests that this may be more interesting than merely evidence of compulsive anthropocentrism and a limited imagination. Surely, we aren’t really trying to grasp the actuality of extra-terrestrials. Or at any rate, the narratives related by believers in and experiencers of UFOs, aliens among us and extra-terrestrial abductions tell us as much about human fears (and hopes) as about the real or fancied activities of visitors from outer space. Bullard is a board member of the Center for UFO Studies (CUFOS), a privately funded research group set up in 1973 to make UFO studies more academically respectable – ‘the flagship of scholarly excellence for the field’. CUFOS was headed until his death in 1986 by Josef Allen Hynek, a professor of astronomy at Northwestern University and longtime consultant to the US air force. He publicly switched from doubter to believer in the fact, at least, of unidentified flying objects, having decided that in spite of all the false sightings there was ‘a stubborn, unyielding residue of incredible reports from credible people’. Bullard echoes Hynek in holding that ‘the body of data points to an aspect of the natural world not yet explored by science’ and goes further, to say ‘that enough threads of coherent experience exist to reject cultural explanations as less than the whole story, though cultural influences contribute much to our interest in the phenomenon even as they do much to confuse our understanding of it. Both sides deserve the serious attention they have never received.’

He describes numerous classical UFO sightings and abduction claims, allowing that many of them were fake or misinterpretations of astronomical or covert military phenomena. Those that remain come from reliable sources, lack alternative explanations, or have a compelling cross-cultural and historical consistency. He says no more than that some stories can’t be accounted for by other explanations. This makes him a surprisingly restrained advocate of little green men. His background is in folklore – his PhD from Indiana University was on that subject – and it inclines him to give far greater cultural and anthropological weight to his understanding of sightings and experiences of the phenomenon of UFOs than you’d otherwise expect. In a subject where the lack of non-anecdotal evidence means it is only possible to believe in extra-terrestrial visits, not to prove them, a cultural description is probably the only alternative to evangelical sermonising. Evangelism works wackily both ways: in 1997, Pat Robertson called for people who believe in ‘space aliens’ to be stoned to death, since if ‘space aliens’ did exist they (and therefore believers in them) would be nothing more than agents of the devil trying to lead people away from Christ.

Stories of sightings and meetings with aliens take up a good deal of The Myth and Mystery of UFOs, and are familiar from science fiction in all its forms as well as reports in newspapers. The mother of all sightings is centred on Roswell in New Mexico, where in 1947 (and as it happens, in the week I was born – just saying) debris was found which was, according to taste, the remains of a crashed UFO or of a military weather balloon from a secret spy programme called Project Mogul. Rumours that dead aliens were found with the debris and hidden in Area 51, a top secret military base in Nevada, were kept alive by a scratchy film that emerged in 1995, showing a large-headed, bug-eyed alien corpse being dissected on an operating table by a man in a white coat. In 2006, the film was revealed by its maker to have been a hoax, but Roswell was the first of a slew of mid-20th-century sightings which supplied the prototype of the conspiracy theory that still circulates among believers. At its most vivid, the story is that the US government made contact with aliens decades ago and formed a secret world government in alliance with them, keeping the masses ignorant and themselves in power. They deliberately mock or ignore believers in UFOs, who are something like seers or liberationists in the face of devilish or imperialist forces of oppression. Close Encounters of the Third Kind fed alluringly off this theory. To more sceptical but still paranoid observers, UFOs at their most plausible are indeed unidentified flying objects: secret military hardware mistaken for something otherworldly. The world government story remains, but the threat is earthly and the solution individual survivalism or Tea Parties. At their most useful as propaganda at the height of the Cold War, evil, non-individualist aliens in American movies and on the radio regularly threatened the earth with obliteration, and with much more determination and animus than Nikita Khrushchev banging his shoe on the desk at the UN.

However, it is Bullard’s account of the myth, rather than the mystery, that offers the most acceptable account of alien sightings and abductions. Or at any rate the most familiar and easiest to take. Aliens who whisk innocent sleepers off to their spaceships and give them medical examinations or impregnate them are only doing what fairies and hobgoblins have been doing since long ago and far away. Perfectly ordinary people in folk stories the world over are regularly stopped on the road and taken away by mischievous or sinister Others. In Western European culture, mermaids drag sailors to the depths, Oberon and Puck do a number on Bottom, Rumpelstiltskin demands a human child of his own in return for a magical favour, the witch entices lost children into a gingerbread house, the inscrutable Pied Piper, dressed half in yellow and half in red, seduces away rats and then, when the citizens of Hamelin prove incorrigible, whisks off the younger generation. In the Bible there was a time when giants walked among us and sons of God or angels mated with fair-faced human females, or appeared to individuals to tell them that they were pregnant with a changeling, or to deliver a warning of things to come and save the world from itself. These stories of underground and parallel worlds have comforted or terrified human beings for centuries. Why wouldn’t we include the space above our heads in our narratives, and why wouldn’t we update the stories? Bullard describes a Zimbabwean sighting at Mutare in 1981. A brightly lit sphere was seen by 20 workers coming back from the fields. It rolled along the ground and then burst into flames. Clifford Muchena saw three men standing observing the fire. They were ‘tall and luminous, they wore silver suits, and a power from them caused him to fall to the ground.’ He told the investigator, Cynthia Hind, that they were the spirits of his ancestors. She pointed out that his ancestors would ‘wear hides and crocodile teeth instead of silvery suits’, to which Muchena replied: ‘Yes, but times change!’ Investigators have cultural limitations as well as witnesses.

Bullard is doing cultural anthropology of a more functional kind, but it’s an effective way of analysing vast amounts of annoying and otherwise unpresentable data. Conversely, the old stories can be reinterpreted from a modern ufologist’s point of view as alien sightings which a non-technological world used its own cultural assumptions to describe. Aliens interfere in very similar ways, dangerous, powerful but compelling. They aren’t angels, but visitors from far-off planets, not ancient questing heroes but high-tech travellers from unimaginable distances. Or they are embedded in the mysteries of the planet so that wonders of ancient architecture and earthworks – Egyptian pyramids, Easter Island sculptures, the Nazca Lines in Peru – are to be taken as evidence of advanced alien technologies fallen into disrepair. They’ve already been and gone. Did they give up on us or were they only passing through and planting a little alien know-how for their own comfort? Anything incomprehensible is available to be either a sign from God or evidence of an extra-terrestrial visitation. Sleep paralysis is used to explain the helplessness of physical abduction experiences, but believers’ stories of what ufologists call ‘high strangeness’ are so compelling that it’s a pity to insist on a terrestrial physicalist explanation.

Either to give his book a what-the-hell pro-believer kick in the tail that non-believers can at least smile at, or because the silliness of the example is so great that it can’t be fantasy, Bullard, the anti-sceptical sceptical director of CUFOS, offers as the most convincing case for the existence of alien visitations the account of an alien raccoon giving the nod to the Nobel laureate Kary Mullis. In his final chapter, Bullard tells of Mullis arriving after midnight (having ‘passed the functional sobriety test’: he’d driven ‘successfully through the mountains’) at his cabin in the woods of northern California in 1985.

Once he turned on the lights and left sacks of groceries on the floor, he lighted his path to the outhouse with a flashlight. On the way, he saw something glowing under a fir tree. Shining the flashlight on this glow, it seemed to be a raccoon with little black eyes. The raccoon spoke, saying, ‘Good evening, doctor,’ and he replied with a hello.

You will have read more than a couple of folk and fairy stories that start like this, to say nothing of Alice in Wonderland, the raccoon being a geographically specific protagonist rather than a white rabbit, a woman of the sidhe from Eire, a biblical angel or a swan formerly known as Zeus, so you won’t be more surprised by the encounter than Mullis seemed to be. Yet for all his clarity about the way alien encounters mesh tightly with older and more terrestrial human legends (those other kinds of Other), Bullard thinks that this is the hardest story to deny. Mullis himself later came across Whitley Strieber’s huge-selling book about his own alien abduction, Communion, and recognised the time he lost that night, but as a chemist couldn’t quite bring himself to accept that he’d been abducted by aliens. Why would they pretend to be a talking raccoon, and anyway, if they’re so smart, how come they invariably have to stick probes up abductees’ bottoms to see what we’re made of? On Star Trek didn’t they have a little gadget that you popped into an alien’s ear and it told you instantly what kind of life form it was? In fact, I think I’ve seen very similar machines used in present-day Las Vegas at the CSI laboratories. So holding back on a definitive yes to alien visitation, Mullis speculated instead that the raccoon ‘was some sort of holographic projection and … that multidimensional physics on a macroscopic scale may be responsible’. And, getting out my Occam’s razor, I too am inclined to prefer the little green talking raccoon from outer space as the more plausible explanation. Bullard’s point is that here is a highly respected scientist who is adamant that something perfectly ridiculous actually happened to him. Mullis, in his autobiography Dancing Naked in the Mind Field, insisted: ‘To say it was aliens is to assume a lot. But to say it was weird is to understate it … It’s what science calls anecdotal, because it only happened in a way that you can’t reproduce. But it happened.’

Believers in all manner of paranormal phenomena regularly argue that science can’t effectively test or falsify such experiences, precisely because it’s normal science. This argument doesn’t help their case among sceptical scientists, but normal science ought to know by now that almost everything has at one time been beyond its capacity to test. Maybe it takes a Nobel Prize-winning scientist to come up with the phrase ‘But it happened.’