Computer modeling of the evolution of the galaxy allows us to resolve the Fermi paradox, according to which alien civilizations cannot go unnoticed, if they exist at all. In the Techno Weekend series, Forbes talks about not very practical, but nevertheless curious scientific and technical ideas
An article by four renowned astrophysicists, published online last month, addresses questions at the intersection of science fiction and cosmology: can intelligent supercivilization colonize a galaxy, and if so, how long it will take.
It is believed that the first such questions were posed by the famous physicist Enrico Fermi back in the early 1950s, and therefore this problem went down in the history of science as the "Fermi paradox". In its most general form, the paradox looks like this: there are hundreds of billions of stars in our galaxy, and it is logical to assume that civilizations arise around some of them from time to time, as happened near our Sun. These civilizations, developing, begin to master the surrounding stellar systems. It is this very promising goal that mankind set for itself in the middle of the twentieth century, and, apparently, it still has not disappeared from the agenda, since our "voyagers" have already left the solar system and are flying to neighboring stars. Thus, advanced civilizations should have enough time to appear in the vicinity of our planet. So where are they?
In 1975, astrophysicist Michael Hart published a famous paper in which he offered the most pessimistic solution to the paradox. At the heart of his reasoning is "Fact A": there are no alien beings in the vicinity of the Earth and never have been. Hart in turn ruled out all possible explanations for this fact associated with the limited speed of interstellar travel and the time of existence of civilizations. There is only one explanation left: alien civilizations simply do not exist. However, many astronomers and cosmologists could not accept this point of view.
Perception paradoxes
Most critics of Hart's ideas point out that he viewed gradual expansion as an inevitable attribute of civilization. This assumption can be erroneous if we take into account another attribute of intelligent beings - psychology.
One of the first considerations, expressed shortly after the Fermi paradox was first formulated, arose, obviously, under the impression of the nuclear arms race taking place on our planet at that time. This argument is that technological development threatens civilization with self-destruction. The absence of signs of an alien visit on Earth may mean that intelligent civilizations, realizing the danger of the unlimited development of technologies, at some point put this development under strict control. Cosmic expansion does not occur, but this does not mean that the superintelligence does not exist or could not master the technique of interstellar travel: it simply did not want it. And those who could not overcome the temptation ceased to exist in accordance with the inexorable laws of history.
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An interesting variation on this point of view is expressed by Sir Martin Rees, the British cosmologist and perhaps the most famous astronomer of our time. He believes that intelligent supercivilization, perhaps, does not manifest itself in any way in our earthly affairs, because it is too immersed in its own thoughts. There are many secrets in the Universe that deserve deep thought, and the longer civilization develops, the more it wants to calmly think about these secrets. An idle vanity, like the conquest of galaxies, does not suit the supermind.
Another point of view is also based on psychology, but not aliens, but humanity itself. It is expressed by Seth Shostak, lead astronomer of the SETI project ("Search for Extraterrestrial Intelligence"). “The clicker bugs in my garden do not notice that they are surrounded by sentient beings - namely, my neighbors and me,” he says. "Nevertheless, we are here." Such an argument may sound a little offensive to humanity, but it is quite reasonable: in order to notice the presence of a superintelligence, you must first at least understand what it is and how it might look, and this in itself is not an easy cognitive task - at least for a beetle …
However, is it possible to resolve the Fermi paradox without constructing hypotheses about the psychology of supercivilizations and without offending humanity? Astrophysicists Jason Wright, Jonathan Carroll-Nellenbeck, Adam Frank and Caleb Scharf set themselves this task. Their simulations offer a more optimistic resolution of the paradox.
Galaxy in motion
In previous models, the arena of supercivilization activity was viewed in the spirit of Giordano Bruno's cosmology: as a space filled with eternal stationary stars. The sphere of influence of supercivilization in this case looks like an expanding bubble around the native star, and the speed of this expansion depends only on the achieved speed of interstellar travel. The authors of the article submitted for publication in The Astrophysical Journal, however, propose to consider our galaxy as a dynamic object.
The picture of the expansion of civilization should strongly depend on the movement of stars within the Galaxy. Our Sun has made about 50 revolutions around the galactic center during its existence, explains co-author Carroll-Nellenbeck of the University of Rochester for the Nautilus project. If we take this fact into account, the intensity of the expansion practically ceases to depend on technological limitations on the speed of interstellar travel. At the same time, the very pattern of expansion changes: instead of expanding spheres, we should see a much more complex picture.
In the simulation, carried out by the authors, the propagation of the "resettlement front" is considered. It turned out that even with conservative assumptions, the galaxy can be populated relatively quickly. However, varying some parameters, such as the lifetime of civilizations and the preference of certain directions of expansion, gave a result that was practically excluded by previous simplified models. It turned out that between the "empty galaxy" and the "galaxy teeming with life" there is a wide sector of other possibilities. In the most probable scenarios, the galaxy is indeed in large part inhabited, but large "voids" remain in it, where the expansion has not yet penetrated. If our star system ends up in one of these voids, which is likely,this can explain the "fact A" formulated by Hart - the absence of visible traces of visits - and thereby resolve the Fermi paradox in a way that is desirable for humanity.
Adam Frank and Jason Wright believe that the main takeaway from their work is this: if we do not yet see traces of the presence of supercivilization in the Galaxy, then we just need to take a closer look.
How to search for extraterrestrial intelligence?
If, as follows from the work under discussion, civilizations following the path of technological progress may well exist in the galaxy, this means that a reasonable direction for their search is to try to find visible traces of this progress, that is, a "technological signature."
Many scientific articles have been written about how such a "signature" might look like. Forbes talked about one of them a week ago: the mathematician Louis Crane wondered what it would look like from the side of a civilization that decided to use miniature black holes created by the radiation of a powerful gamma laser as a source of energy. Another article on this topic was published last week. This time, Brian Lacey of the Institute for Advanced Study in Princeton wondered if we could spot the solar panels of an alien ship from Earth that reached the solar system.
The reflections of solar arrays of near-Earth communication satellites often fall into the field of view of terrestrial amateur telescopes. Lackey's article provides a detailed calculation of the factors affecting the likelihood of such an object being seen. These factors include battery surface area, orientation, and rotational speed. The author showed that the panoramic telescope Pan-STARRS1 in Hawaii, scanning the sky in search of objects dangerous to the Earth, could notice a slowly rotating mirror measuring a couple of tens of meters at a distance of one astronomical unit. However, in order for one such object to get into the telescope frame for sure, their number in the inner region of the solar system must reach a million. Thus, even if an interplanetary spacecraft with huge solar panels is very close to us,the probability of finding it is small.
However, as we saw above, earthly astronomers are rarely content with pessimistic conclusions. Lackey considered the following case: What if the robotic alien station arrived at us a long time ago, went out of use and turned into orbital debris, like the one that mankind produces in abundance? In this case, it is highly probable that it will end its journey at one of the "Lagrange points", where the gravity of different bodies in the solar system balances each other. If you focus observations on such points, Lackey argues, then just a hundred space mirrors are enough to be noticed by one of Earth's small telescopes. Why, then, have they not been noticed yet? Perhaps aliens are just accustomed to cleaning up trash after themselves, the author of the article suggests.
Author: Alexey Aleksenko
