The Fermi Paradox is named after the famous nuclear physicist and Nobel Prize winner Enrico Fermi. At the same time, the scientist himself did not conduct any research on this topic, and this is not part of any of his reports. It’s just that one day during a discussion at a dinner table with colleagues about flying saucers and interstellar travel, he asked: “Where are they all?”, meaning where these aliens are and why we don’t see them.
There are so many planets in the Universe, and for some reason we see life only on ours. Is there still life outside of Earth? Let’s see what some theories say about it.
Is the earth unique?
If we assume that there is an earlier civilization, then why has it not yet conquered the entire galaxy, and we do not see traces of its existence? Full-fledged works discussing this problem were later carried out by completely different scientists. Articles on this topic and even books appear with enviable regularity. And quite recently, several solutions to the Fermi Paradox have appeared at once.
In general, there may be no Fermi paradox at all. We see no one, because there is no one. Despite the prevalence of conditions suitable for life, this does not guarantee its occurrence. Then our Earth is not just rare, but unique. A lot of factors must coincide in order for life not only to originate, but to be able to exist and evolve over billions of years.
There are so many of these factors, and the values of some variables are so sensitive to change, that it seems that the emergence of intelligent life is a very, very unlikely event. Or life (including intelligent life) does not exist anywhere except the Earth. We are the first, so we can’t see anyone. Other solutions allow for the possibility of other civilizations, but try to explain why, nevertheless, we cannot see them.
Highly advanced civilizations and the galactic club
The first recent solution to the Fermi Paradox, which we will consider, allows for the existence of highly developed civilizations that could well begin the expansion of the Galaxy. And we can assume that in this case we should see them everywhere. But here the main question is, for what purpose do they conquer the Galaxy? Maybe they have a need for energy?
There is an interesting opinion that life can originate and exist for so long that it reaches the technological phase, only in stars like our Sun, that is, in G-dwarfs. They are not as dim and active as M-dwarfs, and have a relatively long life – about 10 billion years. However, this may still not be enough. In addition, it is not necessary that the planet will be habitable for all these years.
In which case, civilization may be faced with the need to survive, then it will try to find a new home. And the best candidates for this are K-dwarfs. They live even longer – from 17 to 70 billion years, and the conditions in their systems are most similar to those of the Sun. M-dwarfs are very active and can kill life with their frequent and powerful outbursts. In addition, the habitable zone will be in their tidal capture. In this case, K-dwarfs are the golden mean.
However, they are few: only about 13% of all stars. And not every system has habitable planets. Imagine that some hypothetical extraterrestrial civilization is lucky enough to be close to such a system, and it is waiting for a rapprochement with it in order to get to it less. It is clear that this will take billions of years. Then the aliens will not be everywhere, but near specific stars, and our solar system will be of no interest to them in principle. This situation was called the “Galactic club of K-dwarfs.”
Era of contact
Another recent solution to the Fermi Paradox suggests that we have not entered the Age of Contact at all. Aliens do not come to us, do not send their probes and do not send signals, because they are not interested in us. They may know about the Earth, that there is life on it, but they do not know that there is a relatively advanced civilization on it. In this case, it must be assumed that intelligent alien civilizations exist at all. We also need to admit that the resources of this civilization are limited, which is quite logical. Sending ships or probes to many planets in search of contact could be just wasteful.
Probably, they would simply pay attention to the presence of biosignatures and technosignatures. And they would not be found on Earth. We began to actively send artificial radio signals from our planet about a hundred years ago. Since the speed of light is limited, they flew away for a maximum of 100 light years. If there is someone at such a distance from us, he could theoretically pick up these signals and learn about our existence. At this distance, we know about 15,000 stars.
In order for us to understand that there is someone there, we still need to receive a return signal, so the distance is halved, and this is already 1300 systems. What is the chance that there is an intelligent civilization among them?
To complicate matters, most of the signals are weak and mixed with cosmic noise. This further reduces the chances that someone will find out about us. if biosignatures can be caught from any corner of the Galaxy, then technosignatures can only be caught from a very close distance, and you also have to wait a very long time for these signals to fly far enough. To just wait for the answer to be sent to us, the Era of contact may come in thousands of years. And then there’s the Silent Bubble, the Focal Point, and other theories.
The Silent Bubble scenario explains why we have been unable to pick up signals from extraterrestrial civilizations for 60 years, even though we try very hard. The fact is that on the scale of the Galaxy, six decades is a very short period. Our telescopes have seen so little during this time. What if they are not perfect enough at all and missed a signal that was coming from the other side, which they weren’t listening to?
Perhaps there were signals from extraterrestrial civilizations, but very rare. To such an extent that not a single one has reached us in 60 years. For now, we are in the Silent Bubble. Also, the author of this theory, taking Bayesian statistics as a basis, tried to estimate what are our chances of catching an alien signal. Calculations showed that a 20% chance will come only after 240 years, 95% – after 100,000 years.
Another study not only solves the Fermi paradox, but also explains why these signals can be rare. Perhaps the aliens are just waiting for the right moment. Imagine that a hypothetically existing civilization wants to send us a signal, but at the same time admits that we are not able to listen to billions of stars and planets at the same time. To increase the chance of us receiving a signal, you can choose the best time to send it.
This theory is based on the concept of the Schelling Point or Focal Point. A simple example: when two people want to meet but are unable to contact each other, they need to choose a time and place where they are most likely to meet. Every city has a traditional meeting place. If you add a specific time to it, for example, noon, then this will be the Schelling Point.
We are talking about aliens and the Galaxy, and not about meeting with them, but about receiving at least a signal. To determine the Schelling Point, the theory suggests using planetary transits, that is, when the planet passes in front of the star’s disk from a certain point of view for the observer. Since it is observed from a certain angle for a particular planet, the system must also be turned towards us at a certain angle so that the planet overlaps it along the line of sight from us to the star.
Transits have a predictable and clear period, so both we and the alleged aliens will be able to calculate when and where it will take place. Suppose we can observe the transit of their planet in front of a star, and they know about it, then there is no point in constantly sending signals. They can be directed at the moment when their planet lines up with their star and our planet. Until now, we have not used such a strategy, and maybe that’s why we didn’t catch anything.
And if we start using it, it will not work right away, because there are no fewer systems in space. The research authors even decided to look for signals from twelve planets during transits, and recorded several thousand.
Only two turned out to be worthy of repeated observations, and they are unlikely to be from aliens. However, a list of hundreds of potential targets has already been compiled.
But what if it’s not about the search time, and not about the tools, but about the analysis of the received data? Maybe we received alien signals, but did not recognize them? Or just missed them, because classical analysis algorithms can not cope? The authors of the new study proposed to operate with new algorithms that use machine learning. The data will be analyzed faster, and the results will be more accurate. Moreover, they have already applied these algorithms to 150 terabytes of signal data from more than eight hundred stars in which they had not found anything before. Now there were eight curious signals.
The fact that they were of an unnatural nature was shown by their narrowband range of a few hertz (it is worth clarifying that natural signals are not always wideband). In addition, the signals had characteristics indicating that their source was accelerating away from us. This confirmed that it is not on Earth, that is, it is not a transmitter and not a microwave. Well, the signals were recorded only at certain sources in the sky.
So these signals will be checked in more detail. And scientists will apply their methods not to hundreds of stars, but to millions. The solution to the Fermi Paradox in this case is such that we may have already found something, but we ourselves did not understand it. Such new arguments and approaches give hope for a positive outcome of the search. But how will this end for us?