One of the greatest mysteries that humanity has ever faced is the question of the existence of extraterrestrial life forms.
Many explanations have been offered over the years as to why we should still make the first contact, each better than the other. The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence of their discovery or any contact with aliens is known as the Fermi paradox, or the Great Silence. Let's analyze it point by point.
1. The aliens did not have time to fly to Earth
Actually it was. This is one of the most common explanations for the Great Silence, but at the same time one of the weakest.
The Fermi paradox stems from some pretty powerful principles:
Our galaxy has existed for a very long time - about 13.2 billion years; intelligent life could have arisen back when the galaxy was very young, and thus aliens had plenty of time to visit, colonize, and change every stretch of the Milky Way. Nevertheless, it does not seem at all that any civilization did it.
Over time, our understanding of the universe has been refined, and the Fermi paradox is increasingly challenged. Earlier this year, astronomers concluded that Earth-like planets began to appear as much as 11.2 billion years ago, just two billion years after the Milky Way formed. We now know that the number of potentially habitable planets - both past and present - is enormous. Recent calculations suggest that there are hundreds of billions of Earth-like planets in our galaxy alone.
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2. The stars are too far apart
As Douglas Adams once said:
“The cosmos is great. Really great. You just won't believe how stunningly, unimaginably, dizzyingly large it is. Perhaps you can think that you have a long way to get to the pharmacy, but for space it is sheer trifles."
Yes, there is no doubt that the cosmos is great. But is it for this reason that we do not see signs of the existence of extraterrestrial civilizations? Do all alien civilizations consider space insurmountable to tinker with flights, or that interstellar space travel is technologically impossible? None of this is likely true. Look at us. We already have an interstellar space traveler in the form of probes and there is no shortage of ideas about how we could carry out such missions.
Indeed, the first generation of interstellar conquerors will likely come in the form of self-replicating von Neumann probes that, in theory, could colonize the galaxy in just 10 million years. From the point of view of space, it is not that long. One civilization could have colonized the galaxy 1120 times over the past 11.2 billion years. And that's just one civilization!
So no, the stars are not too far apart - at least not when you have billions of years to work and grow exponentially.
3. Aliens abide by the Supreme Directive
Extraterrestrial civilization at the current stage of its development is very likely to be postbiological in nature and possessing an artificial superintelligence.
Back in 1972, astronomer John Ball came up with the "Zoo Hypothesis" - a scenario in which advanced extraterrestrial life forms deliberately refuse to come into contact with humans in favor of observing them from a safe distance. Ball believes that "they just shut us off as part of the wildlife or zoo." The reasons for this may be a fear of biological or social cross-contamination, that is, the "Supreme Directive", or simply a desire to study us for recreational or scientific purposes.
There are a number of problems with this solution. First, it is completely unverifiable and even a little conspiracy thesis. Second, it is anthropocentric. The zoo hypothesis suggests that all aliens have the same motives in terms of ethics, science, and recreation that we do. This is so presumptuous! What can we offer alien intelligent beings from the point of view of our science? An extraterrestrial civilization at the current stage of its development is very likely to be postbiological in nature and possessing an artificial superintelligence (in fact, it is likely to be an artificial superintelligence). We would be no more interesting to them than microbes.
4. God created the universe just for us
This religious argument attempts to solve the Fermi paradox by assuming that humans were created by God as the only intelligent beings on purpose. This idea goes back to Aristotle and Thomas Aquinas, who argued that humans are God's unique design.
This idea is still popular today, as evidenced by a recent high-profile speech by Pat Robertson, in which he said that NASA should stop its efforts to study space, because it has "nothing but gas balls and wastes," adding that "This planet [Earth] is where God conducts his experiments of creation."
But as Carl Sagan pointed out:
“The universe is a pretty big place. If it’s just for us, then it seems like a waste of space.”
Indeed, if God created the Universe only for us, why is everything so complicated? Why are there trillions of stars in space, and not just one? Simply put, this is an unverifiable argument that runs counter to logic and common sense.
Of course, it is possible that we are alone in the Universe, but in this case there are much better explanations for this than the desire of God.
5. The aliens were here, but then they left
Some argue that aliens have already visited our solar system in the past and moved on, leaving traces of their existence, such as a face on Mars, pyramids and other archaeological finds. Of course, the extraterrestrial origin of the face on Mars has been debunked, and we have explanations for how the pyramids were built (not entirely and not quite as convincing, to be honest). And explanations that try to explain something by the actions of extraterrestrials, although often sensational, are often groundless.
Others claim that aliens have visited Earth long ago, but left without leaving a trace. This is unlikely for several reasons. First, a progressive wave of extraterrestrial intelligence, most likely in the form of a machine, would transform almost everything in its path, transforming matter from inert substances into something more useful. In addition, they can - and probably will - integrate any life into their civilization. In addition, given the age of the Galaxy and its obvious biophilic nature, many different civilizations may visit our solar system more than once. However, according to this proposed solution, none of them remained or left behind any noticeable trace.
6. They are actually already here
The so-called ufologists, who want to make us believe that aliens are already here and right now, torture us with little people of strange anthropocentric physical forms, who abduct everyone on their flying saucers.
To take this seriously, we need material evidence that can be examined at their leisure by skeptical scientists: scraping the hull of a ship and the discovery that it contains isotopic compounds that are not present on our planet, chemical elements from the so-called island of stability are very heavy elements. that do not exist on Earth. Or a material with absolutely strange properties. There are many things like these that would immediately inspire confidence on this score.
But there are no scrapings, no photographs of the ship's innards, no stolen pages from the logbook. All there is is just stories. There are cases of soil disturbance, but I can disturb it with a shovel. There are people who claim to have communicated with UFOs using light signals. But airplane pilots can joke and send you a light signal in response, deciding to pretend to be a UFO. So all this is not sufficient evidence.
7. We haven't searched for aliens long enough
It is true that it was not until the 1960s that we started seriously looking for extraterrestrial intelligence with the advent of Frank Drake's Ozma project. For 55 years we have only scanned the sky, and there are still many areas for radio coverage.
Of course, there is a possibility that no one is receiving or broadcasting signals there. We ourselves are currently discussing all the pros and cons of active SETI (programs for the search for extraterrestrial intelligence) and targeted attempts to attract the attention of aliens. It is possible that all aliens are xenophobes and do not send any radio signals. If so, then all SETIs are doomed to fail.
But if aliens are really interested in getting our attention, they shouldn't have any trouble doing it. They could litter the Milky Way with Bracewell probes - hypothetical communication beacons left in every star system in anticipation of the first signs of intelligent life, such as radio signals. These probes, in turn, would communicate with us, transmitting a signal through a series of communication road stations, other such probes. On the other hand, aliens could broadcast an exceptionally strong and directional radio or optical signal that even such seemingly primitive technological civilizations like ours would not miss.
However, this only applies to civilizations much more advanced than ours. SETI must continue to seek civilizations that are similar to our own in terms of their technological progress.
PS According to various solutions of the Drake equation in our Galaxy there are from 0 (pessimistic assessment) to 10 (optimistic assessment) intelligent civilizations that have and, most importantly, want to establish contact with other advanced civilizations. Another thing is that some of the values in this equation are estimates and extremely subjective, which to some extent devalues the obtained values.
On the other hand, the lifetime of an intelligent technically advanced civilization (at least ours) is extremely short compared to the lifetime of the Milky Way, in order to judge the possibility of establishing contacts with other forms of intelligent life.
In addition, the coincidence of many factors is necessary for our civilization to find aliens, approximately corresponding to earthlings in terms of development. It is much more likely that other civilizations either perished long ago millions and billions of years ago (or are now at such a level of development that communicating with us is the same for them as people trying to talk to ants, sorry for the hackneyed comparison), or now they are just being born and lack the capacity for interstellar contact.