In the sixties of the last century, the search for intelligent life outside the planet Earth began. Sufficient technology was developed to be able to send and receive signals at a distance beyond the solar system. For this reason, we are also in a position to search for technosignatures or technological remnants of other possible intelligent beings.
From this moment on, an interest was generated in the scientific community to find biological and technological markers. This could provide information about other intelligent life forms unknown until now.
For this reason, different observation techniques have been developed that can help us in this search. In this post, we will see several of these techniques.
1. Signs of intelligent life communication – Technosignatures
Radio signals have traditionally been used for this purpose. But recently optical (visible light) and infrared signals have also begun to be used. Typically, we have looked for beacons or lighthouses that emit a signal that we could detect.
The challenge in this search is how to determine whether a signal we detect is an emission made by one of these beacons or is a signal produced by a natural source.
In addition, it is important to keep in mind that this signal must be sufficiently intense or different. So, it is not overshadowed by the star around which the signal-emitting planet orbits.
In the beginning, radio waves were used, because they broadcast at a frequency at which stars do not usually emit. Therefore, when a signal of this type arrives, we can receive it against a background relatively free of radiation of this type.
Recently, however, the possibility of emitting at other frequencies using a laser (visible and infrared light) has also begun to be considered. To make the signal distinguishable from the nearby star, the signal would have to be compressed in time or frequency.
Why? So that it would be a signal sufficiently different from the rest of the naturally emitted light.
By performing these signal transformations, we achieve that much less energy is needed to send the signal over long distances. In addition, the signal sent can be interpreted without any doubt by the receiving source as being of technological origin.
2. Object detection from intelligent life – Technosignatures
These objects or artifacts could be telecommunication systems (satellites, radio transmitters, etc.) that could be in stationary orbits on planets, satellites, or stars. These remains could be found floating freely or on the surface of some planets.
Gigantic structures, such as the Dyson spheres (created by an advanced civilization to extract energy from an entire star), could also be found. They could be emitting energy in the form of heat, or totally or partially covering a star.
Finally, traces of pollutants could also be found in the atmospheres of some planets, charged particles with high energy levels (e.g. radioactive), or particles or objects moving at high velocities, or even energy emitters used for spacecraft propulsion.
As can be seen, it is very difficult to delimit the exact nature of these objects or artifacts.
3. Technology in use or abandoned from intelligent life – Tecnosignatures
The technology could still be in use or abandoned. Even if it is still in use, this does not imply that those who created it are still there. A civilization may have disappeared, and the technology may still be functioning properly.
For this, this technology could have been equipped with self-sufficient mechanisms for obtaining energy, and for repairing or replacing worn or damaged parts.
These structures could continue to generate heat, emit signals, or navigate or maintain altitude in a given orbit indefinitely.
If after slow decay we were to find these structures, they could be floating in dust clouds or on the surface of solid bodies (asteroids, satellites, planets, etc.).
These technologies could even have the ability to grow, multiply, or evolve, so the differences with living organisms could be difficult to determine.
4. Sizes of the found technosignatures from intelligent life – Technosignatures
Since our capabilities for interstellar travel are still limited, the greater the distance at which we wish to observe a given structure, the larger its size must be.
Thus, within the solar system, we can find physical objects of small or moderate size, such as probes or satellites. Also lights moving on the surface of a planet (as city lights would do) or reflections of metallic or glass objects (such as solar panels).
It would also be possible to find chemical traces in localized areas or areas of high thermal emissions. This could indicate the past existence of some kind of civilization.
For longer scales within the universe, one could find belts of satellites orbiting exoplanets, structures located at the Lagrange point (distance between one celestial body and another in which gravity of each counteracts and there could be a body floating between them indefinitely).
Another is the extensive zones that emit reflections on the surfaces of planets. Zones of high heat emission could also be detected.
On scales larger than stars (or even galaxies) one would have to look for Dyson spheres, heat emissions, intense lights, chemical contamination, or systems capable of moving entire stars.
5. Searches for ambiguous technosignatures from intelligent life – Technosignatures
In principle, any signal that does not come from Earth and that has sufficient compression in time or frequency should be of artificial origin. In addition, this signal could be ambiguous (saying nothing or that we would not be able to decipher the message) or contain information that is extremely extensive or universal.
For example, how to develop a powerful technology or the complete history of a galaxy or particular, the opinions, intentions, or feelings of a single sender -an individual- who is sending the signal.
Even if there was no one emitting the signal, it would have enormous value in itself, because it could give us information about the technology used, the sender of the signal, or the type of environment where it was generated.
However, many of the technologies that are discovered could be rather more ambiguous. A particular gas in an atmosphere could be due to natural causes or to an artificial influence.
A set of satellites could resemble an asteroid belt. Therefore, we should be prepared to find extremely ambiguous objects, where it is not easy to find out whether we are dealing with a natural phenomenon, an artifact, or a living being.
6. Technosignatures based on models or anomalies – Intelligent life
On the other hand, two strategies can be adopted in the search for technological markers produced by an intelligent civilization. On the one hand, one can establish models of what would be reasonable or what we would expect to find when finding any of these artifacts (radio waves, heat emitters, etc.).
However, in order to develop these models we should have some prior knowledge of the sociological or psychological characteristics of those who have made them. At the moment, we do not know this information.
The other strategy would be to focus our attention on something that we do not understand or does not fit with our current knowledge.
In this case, we would have to look for objects, events, or situations that stand out prominently from what seems normal or predictable to us. It must be something that does not fit with what seems natural to us.
7. Searching for beacons or eavesdropping from intelligent life – Technosignatures
Beacons or interstellar beacons could give us clear information that someone wants to communicate with us. It would be a technological mark of someone who intends to establish a contact, so it will try to send a signal that is not ambiguous.
However, there could also be beings that are simply communicating with each other and that we could ” listen to”.
Beacons will always be easier to detect, but it cannot be ruled out that we may end up detecting signals that were not intended for us.
The receiving systems used to pick up the signals can detect both types of communication. It would be interesting, before establishing any contact with the sender, to know what his real communication intentions were.
8. Passivity or activity in receiving the messages – Technosignatures
On the other hand, we could settle for passively receiving communications, or we could be more active and request a response from the sender of the signal.
If we decide to be active and request a response, it would create a moral dilemma, because we would be taking a first step that would take many years to provoke a response (because of the transmission speeds known today) and the consequences of this communication could be received (or suffered) by generations long after our own.
Before establishing any type of communication, we should be prepared for any type of response (whether friendly or aggressive). We must take into account that when we want to establish contact with them, we could benefit from this contact, or, on the contrary, they could want to harm us.
Therefore, some authors believe that this type of initiative should be prohibited. Others say it is better to wait until we are ready. While others believe that if we are sufficiently careful in preparing contact messages, they should not provoke any hostile response from the recipients.
A lack of knowledge about the characteristics of the recipients should lead us to take these possible contacts with caution. Even if the recipients had no intention of harming us, the mere information of their existence would likely have a destabilizing effect on our beliefs and our social life.