Any arguments on the subject of extraterrestrial intelligence have always triggered a lot of assumptive statements. Whether they exist. Whether they are advanced. Whether they are intelligent. Whether they have reached the stage of civilization and technological progress. Whether they have been developing in the same way as we do on Earth … One way or another, our planet gives us the only known example of existence of life so far, and having no precise data about other life forms, we can only speculate about extraterrestrial life.
But if we rely on all of these assumptions, and accept that extraterrestrial life exists in its highly-advanced and technologically superior state and, in general, organized in the same way we are, how do we find it? These creatures might not have two hands or soft skin, but their existence can always be confirmed by their technology.
Simply take a look at the moon. Without any geological activity, the moon is able to retain traces of external impacts for millions of years. Recall that such an unstable thing as human shoe prints, only a few during the whole history, are well-preserved since 1969 and have recently been recaptured by the American lunar probe Lunar Reconnaissance Orbiter. And if hundreds of thousands or even tens of millions years ago heavy alien ships landed on its surface or if a possible lunar base for Earth observation existed, the traces may remain under the dust to present day.
Quite likely, the moon is not the only example. It is possible that remnants of extraterrestrial space stations, which lost some of their parts after many years of operation, or even still operational probes, are continuing to work. After almost half a century since space age began, the most far-traveled objects created by people, probes Pioneer and New Horizons have already approached the limits of our solar system. What prevents other civilizations to study us using similar probes? Or maybe try to contact us using radio?
For more than 120 years, our own civilization has been using radio waves to transmit information. During the twentieth century, the Earth was actively “signaling” using radio devices, and although the increasing dominance of digital (including optical) communications is overtaking radio signals, radio-based communication can be deliberately used to send messages into space. Humanity has sent these signals multiple times, why can’t aliens do the same?
The SETI project which has been running since the 1960s, with antennas trying to catch signals in the space static, yielded no results to this date. Some optimists believe that this is nothing short of a surprise, if the signal is out there, looking for it randomly and everywhere at once is useless. So SETI has recently adopted a different approach. Using new data on the availability of suitable exoplanets near stars, its antennas are searching for signals with specific aim, still with no outcomes.
Perhaps the problem is not that alien intelligence does not exist, but that they just do not want to communicate with us? But these “quiet” creatures may reveal some information in the infrared range.
Renowned physicist Freeman Dyson once suggested that at a certain level of technological progress any civilization requiring larger quantities of energy makes it a priority to efficiently capture and use its sun’s radiation. To achieve this, it must design a sphere surrounding the star and absorbing the energy of its radiation or position a dense network of satellites around it. To an outside observer, this “Dyson sphere” heated up from inside will look like radiant infrared ball.
In fact, while absorbing some of the radiation and converting it to a more suitable form of energy, Dyson sphere, in accordance with the principles of thermodynamics, is bound to lose certain amount of energy which is dissipated into space in the form of heat. Gas heated by the incoming radiation in galaxies emits energy in similar fashion, but its emission spectrum will be different.
Russian astrophysicist Nikolai Kardashev proposed to categorize established civilizations into three types according to the level of their progress: those capable of using resources of the planet (type I), resources of the star (type II) and, finally, resources of its galaxy (III). Our civilization is obviously closer to becoming a full-fledged type I, but those “little green men” that are capable of building a Dyson sphere, will already belong to the type II.
“Actually, it does not even have to be a sphere”, Dyson once said. “In fact, it can be any locale in which they create a huge amount of energy and which emits infrared waves”. Indeed, the real solid sphere must have sufficiently strong structure to withstand gravitational pull of the star, and its creation may turn out to be too costly.
According to the scientist, the “sphere” can also be a cluster of a whole group of “artificial biospheres” interconnected and rotating close enough to the star to get enough energy from it. With the average surface temperature of such a biosphere around 27 degrees Celsius, it must emit infrared wavelengths of about 10 microns. It is obvious that the Earth itself radiates a lot of energy in this range, so the search for Dyson spheres must use a telescope located in its orbit. The scientist has formulated all this a long time ago, when orbiting telescopes did not exist, but today the situation has changed.
In 1983, the IRAS probe was sent into space, which was the first orbital observatory supposed to scan the entire sky in the infrared range. “It turned out that the sky is literally filled with infrared sources“, says Dyson. Unfortunately (or maybe fortunately), a great number of them are associated with emission of galactic dust and gas and other natural sources.
Several years later, American astronomer Richard Carrigan used the same IRAS telescope to conduct the first targeted search of Dyson spheres. “In fact, some attempts to locate them have already been made, but systematic search for them has never been done“, says Carrigan.
But his systematic search has yielded no results. Several objects within a couple hundred light years away from us raised scientist’s suspicions, but his attempts to direct SETI telescopes toward these objects and scan them produced no results.
So what about even more remote and advanced civilizations, which Kardashev has categorized as type III, with their ability to use the energy of the entire galaxy? If these highly-advanced aliens create similar Dyson spheres around their galaxies, they could also be noticeable. And Carrigan did not forget to look for these “galactic spheres”, in theory they should be much more noticeable than “star spheres”, but he has not found any.
And not so long ago, astrophysicists at Pennsylvania State University have announced about their project to find Dyson spheres. For this project, Jason Wright and his colleagues have used a tool much more sophisticated than the IRAS probe, which is the modern space infrared telescope WISE. “It is perfectly suited to try to locate Dyson spheres”, he says.
Unfortunately, based on the initial data, WISE experiment has not yet confirmed the presence of Dyson spheres which would block at least 50% of radiation of some distant galaxy. Perhaps astronomers could lower this threshold to 30% or even 20%, and then examine the suitable candidates using other telescopes.
Dyson himself is not sure about the success of this experiment. The scientist believes that this task may take hundreds of years, and still be unsuccessful. Even if alien civilizations do exist, and are technologically advanced, they might not want to communicate with us, and so on…
However, Dyson has another idea which astronomers have not yet tackled. This idea involves traces or bands of ionized gas left behind by spaceships, slowing down after traveling at nearly the speed of light. Such great speed must have a braking distance, which is supposed to have corresponding length, and Dyson suggests that these traces are worth looking into.
It is interesting that for Dyson, the search for predicted or any other objects of extraterrestrial intelligence is not only fascinating by itself, but also because of beneficial effects that they may have on the Earth. Dyson believes that if we locate such an object, it may stimulate the advances in astronomy in order to examine it in more detail as well as boost general progress in science.
“Even if we do not find anything”, agrees Jason Wright, “we can identify the upper limit of energy which advanced civilizations can collect from the stars. And in best case scenario, we might end up finding something very interesting, whether it is an astronomical object of unknown type or something that will immediately get attention of all SETI telescopes”.
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