Search for extraterrestrial intelligence
Decades later, as Enrico Fermi uttered his famous words: "Where is everyone?" – the paradox that bears his name still haunts us. Despite repeated attempts to find radio signals coming from space and our constant efforts to find visible signs of foreign civilizations in remote stellar systems, the search for extraterrestrial intelligence (SETI) has not yet found anything substantial.
But, as history has taught us, failures stimulate new And interesting ideas. For example, in a recent article, Dr. Duncan H. Forgan of St Andrews University suggested that extraterrestrial civilizations could communicate with each other using a transit method. With the help of such a "galactic Internet", advanced species can try to send signals to us right now.
Soon was published an article by Forgan "The passage of exoplanets as the basis of the interstellar communication network." In addition to being a research fellow at the School of Physics and Astronomy, as well as the Scottish University Physical Alliance at St. Andrews University (the oldest school in Scotland), he is also a member of the St Andrews Center for Exoplanets.
The article begins with an examination of two fundamental problems related to interstellar communication – time and energy consumption. When it comes to things like radio broadcasts, the amount of energy that will be required to transmit an agreed message to interstellar distances is huge. Optical communications (i.e., lasers) need less energy, but their detection will require an incredibly accurate time.
Thus, none of the methods would be reliable for creating an interstellar communication system. Taking into account recent efforts to detect exoplanets, Forgan argues that the method of passing before the stars, which is the basis of communication, solves both problems. The reason for this is largely due to the fact that the transit method is currently one of the most popular and reliable methods for detecting exoplanets.
Observing the periodic decreases in brightness that are caused by a planet or object passing between the observer and the star, Astronomers can determine whether the star has a system of planets. This method is also useful for determining the presence and composition of the atmosphere around the exoplanet. As Forgan points out in the document, this method can be used as a means of communication of other civilizations:
"ETI 'A' can communicate with ETI 'B' if B observes the passage of the planet in star system A, or by creating structures for Artificial passages observed by B, or by emitting signals B during transmission at a much lower energy consumption than conventional electromagnetic transmission schemes. "
(ETI is an acronym for Extraterrestrial Intelligence.)
] The Inhabited Zone of the Milky Way. Image: NASA / Caltech
In short, Forgan argued that in the Galactic Inhabited Zone (GHZ) – the region of the Milky Way, in which life is most possible – species can discover that the best way to communicate with each other Another is the creation of artificial megastructures for the passage of their star. These passages that other civilizations seek will lead them to the conclusion that there is a developed civilization in another stellar system.
He even offers estimates of how often such transmissions can be made. According to him:
"The message with a range of 20 kiloparsec (diameter GHZ) has a total travel time at a light speed of less than 0.06 million years. If we assume a relatively short period of time during which both ETIs remain in the transit zone for 100,000 years (which is close to a time scale on which both the evolution of the planetary orbits and the star orbit are important), then only 30 exchanges can be made. This, of course, does not prohibit communication in other ways. "
The possibility of extraterrestrial life
If this is familiar to you, then probably because some theorists think that this is happening around KIC 8462852. As early as May 2015, astronomers noticed that in the last few years, the star had seen significant dimming. This behavior ran counter to natural explanations, which led some to argue that this could be the result of someone else's mega-structure passing in front of the star.
According to Forgan, this possibility is hardly contrived and will in fact be a relatively economical means of communication with other advanced species. Using the theory of graphs, he calculated that civilizations inside GHZ can create a fully connected network for a million years, where all civilizations communicate with each other (either directly or through intermediate civilizations).
KIC 8462852, which over the past few years has experienced unusual changes in brightness, in the artist's view. Source of the image: NASA, JPL-Caltech
Not only will this network require much less energy for data transmission, but the range of any signal will be limited only by the scale of these civilizations themselves. In addition to saving energy and increasing range (provided that intermediate civilizations can transmit messages), this method offers other advantages. First, to ensure the passage of exoplanets requires a high level of technological complexity.
In other words, civilizations need to reach a certain level of development before they can hope to join the network. This would prevent any unfortunate "cultural pollution" when less developed civilizations learned about the existence of aliens before they were ready. Secondly, when they are received, the signals of the transit network will be extremely predictable, and each transmission corresponds to a known orbital period.
But there are some disadvantages that Forgan drew attention to. The frequency of these signals would be a double-edged sword, since the signals could be sent only when the receiver was caught passing. And although the megastructure can be moved to change the transit period, this creates problems in terms of synchronization of transmission and reception.
Turning to the limitations of analysis, Forgan also recognizes that the research is based on fixed stellar orbits. It is known that the orbits of stars change with time, for the stars regularly enter and exit the GHZ on cosmic time scales. In addition, there is also the question of how such a network will differ from denser regions in the galaxy, for example, globular clusters, and zones filled with free stars. Double stars are also not considered in the analysis.
Can extraterrestrial megastructures be the key to interstellar communication? Image source: Kevin Gill
It is known that planetary orbits change with time due to disturbances caused by neighboring planets and stars or close-passing stars. As a result, the visibility of the passing planets can change even more in space-time scales. Last but not least, research suggests that civilizations have a natural life cycle of about a billion years, which is not based on any specific knowledge.
However, these considerations do not change the general conclusions made by Forgan. Taking into account the dynamic nature of stars and planets and believing that civilizations exist only 1 million years, Forgan argues that the creation of an interstellar network of this kind is still mathematically feasible. In addition, an artificial object can continue to signal other species after the civilization has died out.
Turning to the Fermi paradox, Forgan concludes that this kind of message will take a long time to be discovered. As he summarizes in the article (highlighted in bold):
"I believe that at any moment only a few civilizations are correctly located to communicate through the transit method. However, we should expect that the real network will be cumulative, when a "handshake" at any time guarantees a connection in the future through, for example, electromagnetic signals. In all our simulations, the aggregate network connects all civilizations together into a whole network. If civilizations exchange knowledge about their connections, the network can be fully completed in terms of the order of hundreds of thousands of years. After creation, this network can connect any two civilizations either directly or through intermediate civilizations, with distances much smaller than the dimensions of the GHZ. "
In short, the reason why we have not yet received or found ETI evidence may be a matter of time. Or we just did not understand that they were communicating with us. Although such an analysis is based on guessing and, possibly, on anthropocentric assumptions, it is certainly fascinating because of the opportunities that it represents. He also offers us a potential tool for searching for extraterrestrial intelligence (SETI), which we are already dealing with.
So many stars, so many planets. So many connectivity options! Source of the image: ESO / M. Kornmesser
Last but not least: he offers a potential solution to the Fermi paradox, which we may have already stumbled upon and just do not know about it. As far as we know, the observed brightness drops, originating from the star KIC 846285, indicate a strange civilization (possibly extinct). Of course, the key word here is "possible", since there is no evidence that could confirm this.
The opportunities discussed in this article are also interesting given that hunting for exoplanets will grow in the coming years. With the deployment of next-generation missions such as James Webb Space Telescope and Transiting Exoplanet Survey Satellite (TESS), we expect to learn much more about star systems in both near and far space.
Will we find more examples Unexplained brightness drops? Who knows. The fact is that if we find them (and do not find them a natural reason), then we have a possible explanation. Perhaps our neighbors invite us to "connect"!