By the mid-20th century, the UFO phenomenon was beginning to gain momentum and the issue of alien life was entering both popular culture and the discussions of scientists. One of these took place on a summer day in 1950, when four physicists were having lunch in the dining room of the Los Alamos laboratory (USA). Statistically, they reasoned, there should be countless civilizations in the universe. “So, where are they?” asked Enrico Fermi. The anecdote gave rise to what is known as the Fermi paradox, the apparent discrepancy between what reason tells us and what we observe: to date, we have no proof of alien life, intelligent or otherwise. Over the years, multiple solutions to this paradox have been proposed. We review some of them below.
They are too far away for any contact
Although science fiction films have accustomed us to the idea of interstellar travel and encounters between beings from very different places of origin, reality imposes a drastic limitation: even communications cannot travel faster than light. The diameter of our galaxy is over 150,000 light years. We have been broadcasting radio signals for just over a century, so our presence could only be detected within a radius of about 100 light years around the Earth. A picture published by The Planetary Society illustrated how ridiculous the current expansion of our transmissions is on the immense scale of the Milky Way.
This same limitation applies to the possibility of receiving signals from other civilizations, given that the speed of light is universal. In 2016, a study introduced into a model certain estimated parameters on the distribution of stars in the galaxy and the possible frequency of the existence of life, and concluded that only 1% of the galaxy may have already been covered by radio transmissions from different planets, and that we will still have to wait about 1,500 years to have a decent chance of being reached by some alien broadcast.
We’re the first ones and we’ll be extinct before there are any others
In 1961, the radio astronomer Frank Drake gave algebraic form to the already established idea about the multiplicity of intelligent life in our galaxy. The so-called Drake equation, which tries to estimate this number of civilizations, has been re-evaluated countless times by other scientists, but generally with the result that these other beings must be abundant. However, even accepting this optimistic view, some scientists have drawn attention to the fact that estimates like the Drake equation do not take into account that a civilization is born and dies, and that in the life journey of the universe, the two need not overlap in time.
In 2015, two astronomers from the Space Telescope Science Institute estimated the possibility of other civilizations in the universe at 92%, but throughout its entire history; the bad news was that 92% of planets similar to ours in the entire history of the universe have not yet been formed. The conclusion is that we humans have emerged too early, and we will probably not be here when other intelligent beings appear. What’s more, according to a certain hypothesis, the fact that we have arrived first could prevent anyone else from coming into existence, if it were to happen that the expansion of a civilization tends to eliminate others without even realizing it.
We are being observed without our knowledge: the zoo hypothesis
Space exploration pioneer Konstantin Tsiolkovsky already reflected on the Fermi paradox in his manuscripts decades before Fermi himself. In 1933 he wrote that alien beings, infinitely more advanced than we are, would find the same interest in communicating with us as we would in trying to communicate with wolves, snakes, or gorillas. Forty years later, radio astronomer John Ball arrived at a similar vision, stating that aliens “have set us aside as part of a wilderness area or zoo.”
This so-called zoo hypothesis, that other intelligent creatures observe us without revealing their presence, we being to them like animals in a nature reserve, was examined in 1977 by Thomas Kuiper and Mark Morris, who argued that aliens keep us in quarantine until we can offer something usable. These ideas continue to occupy the theoretical thinking of some scientists. However, when taken to the realm of simulations, this deliberate isolation agreed upon by all the other civilizations would require a synchrony among the members of the so-called “Galactic Club” that probably cannot occur in our galaxy.
They’re hibernating, or waiting
Ideas such as those mentioned above often attract the interest of those who believe in a universe overflowing with life about which we still have no news. But this does not deter scientists from playing with other imaginative solutions. One study launched the hypothesis of aestivation: if a super-intelligent civilization had succeeded in replacing its biology with machines, it might be waiting for the expansion of the universe to cool it down in order to increase the efficiency of its computations.
According to another idea, aliens could take advantage of the relative movements of stars to travel only when the destination is closer, just as we earthlings send spacecraft to Mars when it is nearer to Earth. So perhaps they visited us 10 million years ago and won’t visit again for a long time.
There is no paradox: there is no one else
All of the above assumes that those millions of civilizations we have not yet contacted actually exist. But not all scientists agree with that assumption. As an example, in 2018 researchers at Oxford University argued that the possibility of the emergence of life has been overestimated in the Drake equation. With the readjustment proposed by these authors, this is their conclusion: “We find a substantial probability of there being no other intelligent life in our observable universe.” Specifically, they put the chances of us being alone in our galaxy at between 53% and 99.6%, and in the entire observable universe at between 39% and 85%.
The only thing that is certain is that all of the above is purely speculative. But for some biologists, starting with Nobel Prize winner Jacques Monod in 1970, the fact that on our planet, which is so conducive to life, life has emerged only once in billions of years does not support the prediction that it will be a commonplace phenomenon. At the very least, certain authors postulate, it is a lot to assume that there is an inevitable path from a simple cell to complex life and to a technological species. According to the Great Filter hypothesis, along that path there are evolutionary bottlenecks in which something usually goes wrong, frustrating the possibility of the emergence of a species capable of wondering if there is anyone else out there.