Extra-terrestrials have been imagined for at least 2300 years, if not longer. Epicurus wrote to Herodotus in 300BCE proposing there could be "infinite worlds both like and unlike this world of ours", even ones inhabited by "living creatures and plants and other things we see in this world"1.
“When he redesigned the cosmos, Descartes diminished the significance of human beings by opening up the possibility of life elsewhere. The concept of multiple universes was strange and new, but by the middle of the eighteenth century, many natural philosophers believed not only that they existed, but also that they provided homes for intelligent beings.”
It is really hard to guess as to how many places in the Universe intelligent life has developed. You need to know things like how many habitable planets there are, what the chances are of life developing and what the chances are of life surviving long enough to develop as we have (and beyond). Seven such factors were formulated into a single construct known as the Drake Equation in 1961, by astronomer Francis Drake3. The result of this is as estimate of how many times advanced civilisation has appeared in the Universe. But so many of the necessary values were unknown, that previous generations of scientists have concluded that the error margins are too high to draw any conclusion4. However, advanced new telescopes and the slowly dawning space age have allowed many more accurate measurements to be made and current calculations are that life may have arisen on one hundred billion Earthlike planets throughout the Universe if using some dire statistics on how likely life is to appear on any given planet (one in a billion).
Unluckily, the distances between stars and galaxies in the Universe are so unimaginably large that, although hopeful data hints at a large number of inhabited planets, it is still unlikely that there is life nearby or even within the traveling distance of a hundred lifetimes. Even at the speed of light, the distances involve make traveling to alien planets a one-way journey. Out of all the UFO sightings, where there has been reliable evidence it has lent itself to terrestrial explanations rather than extra-terrestrial ones5. Where there is no evidence, though, many people cling, out of hope or fear, to the idea that UFOs are aliens. It seems that in the absence of evidence people assume that 'sightings' are aliens even though wherever evidence has emerged, it has pointed to Earthlings as the source. Responsible scientists such as those at SETI complain that their science-based approaches are sometimes confused with UFO-ology. Its director Dr Seth Shostak said it makes him "squirm" and emplores that next time someone is abducted by aliens, won't they please bring back at least a piece of physical evidence?6.
“[UFOs] tell us absolutely nothing about intelligence elsewhere in the universe, but they do prove how rare it is on Earth.”
Arthur C. Clarke7
It is considered a matter of common sense to admit that the popular press play up and exaggerate stories, including (and especially in previous decades) when it comes to UFOs. The press behaved in the same way as it did with other 'moral panics' - with much sensationalism, and with disregard for evidence8. But it wasn't until I read the research of Martin Gardner that I realized just how much of a role imaginative newspaper editors had played in the creation of the UFO craze. It started in 1947, when Kenneth Arnold saw 9 small weather balloons that were strung together, 'flying' in formation in the sky. The papers came up with the idea of 'flying saucers' on their own, and henceforth, enthusiastically published hyped-up articles attributing all unidentified flying objects to mysterious advanced technology and aliens. It was a science-fiction decade, with a popular press to match.
Aside from the press, hoaxes added to the numbers of reports. Three military men lost their lives investigating UFOs such as those seen near Maury Island. Gardner reports that "the entire Maury Island episode later proved to be a hoax elaborately planned by two Tacoma men who hoped to sell the phony yarn to an adventure magazine. Both men eventually made a full confession"9.
“At first the military forces brushed aside the flying-saucer mania as mass delusion, but after the reports grew to vast proportions, the Air Force set up a "Project Saucer" to make a careful investigation. After fifteen months they reported they had found no evidence which could not be explained as hoaxes, illusions, or misinterpretations or balloons and other familiar sky objects. [...]
A book could be written about flying saucer hoaxes perpetrated in the past few years by pranksters, publicity seekers, and psychotics. Unfortunately, exposure of the hoax seldom catches up with the original story.
Even more difficult to expose are the semi-lies - accounts which have a basis in fact, but may be grossly exaggerated. For example, an observer sees a balloon but is convinced it is a saucer. Others are skeptical and this irritates him. So to convince them, he adds details, or exaggerates what he has seen. He may do this without being aware of it, and later recall the episode not as he saw it, but as he has added to it in his desire to convince himself and others. This is a well-known human failing and there is no reason to suppose it could be involved in hundreds of so-called saucer sightings.”
“We all suffer from systematic cognitive dysfunctions; they infuse the very way we notice and analyse data, and distort our forming of conclusions. Even our very perceptions are effected by pre-conscious cognitive factors [...]. Our brains were never meant to be the cool, rational, mathematical-logical computers that we like to sometimes pretend them to be.”
Investigation of UFOs has always found, where evidence is available, that the source of the sighting is an optical illusion, a result of human error or misunderstanding, or normal skybound objects that the observer has mistaken for something spooky. The example of Skyhook balloons teaches us much about the human predisposition to prefer exciting and stimulating theories to normal and mundane ones. First, the basics:
“[In 1951 Feb] the Office of Naval Research distributed a ten-page report on the Navy's huge skyhook balloons, used for cosmic-ray research. The report pointed out in detail the ease with which these giant plastic bags - a hundred feet in diameter - could be mistaken for flying disks. The balloons reach a height of 100,000 feet, and are often borne by jetstream winds at speeds of more than 200 miles per hour. If the observer guesses the balloon to be farther away than it is, then, of course, estimates of speed can be incredibly high.
At a distance, a balloon loses entirely its three-dimensional spherical aspect. It takes on the appearance of a disk [and] a globular object viewed through a telescope looks remarkably like a plate. [...] The plastic composition of a skyhook balloon offers a surface that seems highly metallic in reflected sunlight. Most of the saucer reports describe the disks as silvery in color. At sunset the balloons may shine in the sky for thirty minutes after the earth has become dark [due to their height]. "If your imagination soars," the Navy release said, "[...] The wisp of the balloon's instrument-filled tail may impress you as the exhaust. The sun's rays may suffuse the plastic bag to a fiery glow" [...].
One of the few points on which all observers of flying saucers agree is that there is no noise. This excludes, of course, any known type of propulsion, but is precisely the way a balloon behaves. Observers have sometimes insisted that what they saw could not be a balloon because it was moving against the wind. They forget that wind directions in the stratosphere may be quite different from wind directions on the ground. [...]
The first skyhooks went up in 1947, the year flying saucers were first reported. [...]
At the time of the Navy's report, 270 skyhooks had been released from various spots in the United States, often remaining in the sky more than thirty hours. Frequently, lost balloons were actually traced by following press reports of flying saucer sightings!”
We are inclined towards seeing things in a more dramatic and exciting light. We learn that before concluding extraordinary things, we should first check our basic perceptions and thinking processes because our perceptions and ideas can cause us to fool ourselves.
Let us presume that we have detected intelligent aliens, 100 light-years away. This is not a long way but still covers a thousand stars and their planets. If we want to communicate with someone who we know exists, who probably do not know we exist we must first attract their attention. Someone could be trying to contact us but so far we could have missed the signal by unfortunately not facing a receiver in the correct direction!
If we sent a message to them it would take 100 years to get there. They would have to detect it and then send one back, which would take another 100 years. This means that a reply would take 200 years from the time our first message was sent. This is the fastest possible two-way communication allowed by the laws of physics. And this assuming they are close by. We would have to keep scanning from about 190 yrs after our first message up to 250 years after our transmission to see if they have replied to our one message. We would have to keep re-sending the signal for the 100 years in case they have not detected it yet! Only when we receive a response could we stop resending the original signal. Even if we did discover intelligent alien life in our lifetimes we certainly would not be alive to learn the outcome. If Human life was extended to beyond 200 years on average then perhaps it would seem more exciting - the prospect of still being alive when we are expecting an answer!
How long would it take us to establish a dictionary of mathematical terms with which to communicate? Depending on the length of the transmissions (they would have to be highly repetitive in order to be easily recognizable and to prevent data corruption) it could take well over a thousand years to learn anything about them, or them about us, apart from the fact that we both have well-financed radio astronomers and reasonable mathematicians.
If we receive transmissions from further away, they could have been sent thousands or even millions of years ago. We have to consider the very likely possibility that by the time signals have bounced around the Universe for long enough to accidentally stumble upon the antenna of an intelligent species, the original sender, their planet, and their sun, are all extinguished, and such a frustrating event is one that sorely worries astronomers and scientists10.
On the other hand, luckily, our transmissions into space actually got a head start on our present intention to find life in the Universe:
“Humans have been sending radio waves into space at the speed of light for nearly one hundred years now. Although our goal has seldom been interstellar communication, radio is especially appropriate to that task because electromagnetic waves generally require no travel media, and because radio waves penetrate very efficiently through gas and dust clouds. To date, our "radio bubble," as Tyson calls it, encompasses every star around which a planet has thus far been found, including Alpha Centauri, at 4.3 light-years away; Sirius, our sky's brightest star at ten light-years out; and about a thousand others. So, if aliens are listening, they might have an opportunity to partake in any message sent at frequencies greater than twenty megahertz, including FM radio and television.”
The mechanics of listening to such weakened signals requires massive effort, massive receivers pointing in the right direction, "and, if the yearning stargazer actually wanted to decode our message's content, it would have to first adjust for Doppler's shifts caused by Earth's rotation and revolution, and then build a dish about twenty miles wide, or four hundred times Arecibo. That's a lot of work - and for what? A weekly dose of Desperate Housewives and reruns of Welcome Back, Kotter"5.
So although we might despair at the vastness of space, the remoteness of life on Earth and the incredible chances against radio waves happening to travel from one inhabited planet to another, we might also get lucky. I explore the potential results of discovering alien intelligence in: "Discovering Alien Intelligence: The Politics of War and Fear" by Vexen Crabtree (1999).
Searching for aliens via their radio emissions may not prove to be that useful. Satellites and probes which we have sent into space transmit their radio signals in a directional manner (which saves energy) back towards the Earth, meaning, that often our transmission don't just spread across the Galaxy, but head straight for Earth. It would take an incredible stroke of luck for such intelligently directed signals to be intercepted or spotted by anyone that they were not directed at. Likewise we are unlikely to accidentally stumble across alien communication channels - the alien planet's network of satellites and spaceships, needless to say, will do most of their communicating (just like ours) by transmitting directly to their home world(s).
The same problem occurs with our own "radio bubble", expanding outwards from Earth. Unlike terran omnidirectional antennas, our transmissions that escape into space are not omnidirectional. Our radio bubble is not like a detectable shockwave, but rather, like a very thinly spread net. Signals in space do not spread out the further they travel, like they do within a planet's atmosphere. With no media such as air to travel through, radio signals travel in long, but very thin, straight lines. You have to be within the direct path of this lightspeed needle in order to detect it. "When you consider that entire galaxies can pass through one another without any stars colliding, you can get some idea of how empty the universe is. [...] Any signal from any planet in the universe broadcast in any direction is unlikely to be in the path of another inhabited planet" says Robert Todd Carroll13, "if you were a magical massless being who hopped aboard a photon shot from Earth in any direction, it is highly likely that you would pass through the entire universe without hitting anything larger"10.
Now, in addition to all that, Human use of radio transmissions is dwindling. Things like the Internet have replaced radio as a good default method of communication, but, do not use radio waves that might travel into space. Paul Davies, physicist at Arizona State University, states that the mass use of radio may not persist, and already we have largely moved on to use things like fibre instead. 'Moreover, many modern radio devices (such as mobile phones) rely on a technique called 'spread spectrum' encoding. It uses signals that look like background noise, except to a receiver equipped with the right unscrambling code. Us Humans figured this out within a century of inventing radio technology, so aliens might have done the same. Radio signals that are clearly artificial in origin may, then, be only a transient sign of civilisation.'14 In other words, planets harbouring intelligent life probably only emit radio waves (just like us) for a short period in their development. To be in the right spot, in the right direction, and have receivers pointing in the right direction, at exactly the right point in time, requires a bit more luck than many scientists hold out for.
One possibility considered by Paul Davies, a physicist at Arizona State University, stems from a problem that our species will face in the future: the death of our star, the Sun. Star manipulation, in order to make it last longer, or to shield it, or obtain more energy from it, could be a tell-tale sign of an ancient civilisation trying to protect itself from the star's demise.
“Red giants are created when a star exhausts its supply of hydrogen at its core, with the result that the inner layer contracts and the outer layers expand, forming a redder and much larger star. If a star's outer layers could be mixed into the core, that would slow the process of inflation down. [...] Such a star would look odd, though. It would be bluer than it should be and would be of a type known to astronomers as a 'blue straggler'. [...] Perhaps, then, it will be a sign like this - of a technological civilisation millions of years old - that is seen, rather than some upstart that has not even got its radio waves under control.”
So it might be that although SETI using radio waves is not likely to bear much fruit, it is possible to use some similar techniques but shifting the emphasis to stellar spectrography.