Since ancient times, the inhabitants of the Earth have wondered: are there other intelligent beings in the depths of space? Is the phenomenon of intelligence unique, or is it as widespread as the planets and stars? In the 20th century, for the first time, mankind had a fundamental technical opportunity for communication with hypothetical civilizations in other stars. But passive waiting for a signal from "neighbors" has not yet led to success. Does this mean that we should move on to more active action?
Even Blaise Pascal in the distant 17th century shared his experiences: "The eternal silence of these endless spaces terrifies me." In the middle of the last century, the famous science fiction writer Isaac Asimov very succinctly formulated the question of extraterrestrial civilizations: Are We Alone? ("Are we alone?"). And soon the American science journalist Walter Sullivay responded by publishing a book in 1964 called We Are Not Alone ("We are not alone"). But, unfortunately, this title only expressed hope, not a scientifically established fact.
Science cannot yet give any definite answer to this question. Nothing fundamentally prohibits the very possibility of the emergence of life and intelligence in other stars, however, it is still impossible to estimate statistically this probability - after all, we do not even know in detail how they appeared on Earth, not to mention the fact that we do not yet have a single example of alien life … Soviet astrophysicist Joseph Shklovsky, originally a great enthusiast in the search for extraterrestrial intelligence, at the end of his life did not rule out that humanity may well be the only civilization in our Galaxy, if not in the entire Universe.
SETI and METI PROGRAMS
Because of such high uncertainty in the answer, the question itself is often considered unscientific. The formation of such an attitude was largely facilitated by science fiction writers and especially ufologists, who largely discredited in the eyes of the public the very idea of searching for extraterrestrial intelligence. As a result, not a single state has financed searches for extraterrestrial civilizations in recent decades. But fluctuations in public opinion do not remove the very fundamental question: are we alone in the universe? And the answer to it cannot be approached without trying to discover an alien intelligence.
Space research data practically exclude the possibility of finding aliens in the solar system. Therefore, in their search it is necessary to focus on other stars. Physically, we still cannot get to them, and therefore the only real possibility of establishing contact is the exchange of electromagnetic signals that propagate in space at the speed of light.
Solving this problem, you can adhere to two strategies: either only look for signals from other civilizations, or, along with the searches, send messages themselves in the hope that someone will accept them, decipher them, and then send us an answer. These two approaches became known as SETI and METI, from the English expressions Search for and Messaging to Extra-Terrestrial Intelligence, meaning, respectively, to search for and send messages to extraterrestrial civilizations.
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FOUR INTERSTELLAR LETTERS
The earthly history of searching and transmitting intelligent signals is relatively young. It all started with two pioneering works by American scientists. In September 1959, J. Cocconi and F. Morisson published an article Searching for Interstellar Communications in the scientific journal Nature, in which they analyzed the technical feasibility of interstellar communication from the point of view of radio astronomy and information theory. And in 1960, Frank Drake at the American Radio Astronomy Observatory "Green Bank" conducted the Ozma experiment - the first attempt to detect artificial signals from space.
Unfortunately, searches have failed since then. There are many reasons, but the main one, perhaps, lies in the fact that the volume of searches undertaken so far is absolutely negligible, if we compare it with what actually should be examined. This can be partly explained as follows: until recently, not a single specialized instrument was created for the needs of the SETI program - all searches were carried out in fits and starts on conventional radio and optical telescopes. High hopes are now being placed on the Paul Allen Antenna Array, the first dedicated SETI instrument being built in California with funding from one of the founders of Microsoft. In mid-2008, the first 40 of the 350 six-meter parabolic antennas of this system went into operation.
The sending of the first interstellar messages is also associated with Drake's name. In 1972, he collaborated with Carl Sagan to create The Pioneer Plate, and in 1977, Voyager's Golden Disc. These metal carriers with information about humanity went to interstellar space aboard the Pioneer and Voyager spacecraft, which, after flying past the giant planets, were to overcome solar gravity and leave our planetary system forever.
Instruments capable of sending interstellar messages
In 1974, immediately after the first interstellar radio message was sent from Arecibo, Nobel laureate radio astronomer Martin Ryle issued a press release demanding a ban on any attempts to broadcast from Earth to alleged extraterrestrial civilizations. Other civilizations, if they really exist, are most likely more advanced than ours, which has just begun active exploration of outer space. It can be dangerous for humanity to attract the attention of these powerful forces, Martin Ryle believed.
Frank Drake, one of the authors of the Arecib radio message, objected: “It's too late to worry about being discovered from outside. It is done. And it goes on day after day, with every television broadcast, every sounding signal of the military radar, every command issued on board the spacecraft … I suppose the hostile warlike tribes, whether terrestrial or alien, will destroy themselves with their own weapons long before how they can get at least some idea of interplanetary travel."
The same instruments that were used for the MEL program have been used in planetary radar experiments for more than two years in total, while the total duration of METI sessions today is only 37 hours. Moreover, the area of the sky covered in the METI experiments is thousands of times smaller than that illuminated during space radar. Therefore, talk about the danger of METI because of the possibility of our detection precisely because of the transmission of interstellar radio messages does not look very convincing.
Along with METI-phobia, there is SETI-phobia, which, paradoxically, has more serious reasons. Even if one does not assume any particularly malicious nature of the senders of the interstellar message, the very fact of receiving a sufficiently large array of alien information on Earth is fraught with a latent threat. Competition between countries and corporations can sharply aggravate if the information received is expected to provide radical strategic advantages to the one who deciphers it first. And from here it is already one step to a serious military conflict. There is an even more sophisticated scenario, according to which competition will lead to lower safety standards when translating the message. And it may contain instructions for creating a computer with powerful self-learning artificial intelligence. This intelligence, on the one hand,can help humanity in solving various problems, thereby entering into trust, and on the other hand, it will beat this humanity, like a grandmaster of a newcomer, take control of all resources and send them to further distribution throughout the Universe of the same viral message. And, what is most unpleasant, if such a scenario is really real, then most of the potential SETI messages must be carried by viruses. It is difficult to oppose something to such sci-fi scenarios, since there are too many assumptions that are specially selected to create the most unfavorable scenario for humanity. Perhaps, it is worth noting that faster or slower, but the SETI program will still be implemented, simply because there are enough people in the world who are interested in this and who want to get in touch with extraterrestrial civilizations. Carriers of SETI phobia are unlikely to be able to stop them everywhere. And if at least someone transmits their messages into space, then sooner or later they will be accepted. So even if there are some threats associated with them, it is better to calmly prepare for them than to try to hide from fear in your galactic corner.
ACCEPT OR SEND?
Thus, in the entire history of earthly civilization, only four projects for the transmission of interstellar radio messages have been developed and brought to practical implementation. And yet, in a sense, METI is in a better position than SETI. After all, having prepared and sent an interstellar message, we can already talk about the result, since we did our best to establish a radio bridge between the terrestrial and the supposed extraterrestrial civilizations. And now it depends only on unknown addressees whether our "letter" will be found and attempts to establish contact will be made.
A civilization that only searches is in a noticeably less advantageous position than one that, along with searching, also transmits signals. To understand that contact has been established, it is enough for the transmitting civilization to receive an answer to one of its messages. But if the search is successful, the “listener” will have to send a response signal herself, wait for confirmation of its reception, and only after that it will be possible to talk about the contact. However, there is another side to the problem: if alien signals are detected, it will immediately become clear where to send your own messages, and before that it remains only to send out "cosmic spam", choosing directions based on general physical arguments.
This choice became much easier after the Swiss astronomer Michel Mayor and his graduate student Didier Quelotz discovered the first planet outside the solar system near the star 51 Pegasus in 1995. Soon, the identification of such objects was put on stream, and it became clear that planets are the same common celestial objects as stars. There are about 100 billion stars in our Galaxy, and about 1% of them are similar to the Sun. It is among this remarkable billion that stars should be selected for the search and transmission of interstellar radio messages. Of course, it is not at all necessary that potential addressees live only with such stars, but nevertheless, given our own experience, it is worthwhile to concentrate our research on them.
The list of requirements for stars - candidates for inclusion in the SETI / METI program is quite extensive. First of all, they must belong to the so-called main sequence, that is, be in the middle of their life path. At this stage, the luminosity of the star remains approximately constant for a long time, which, apparently, is an important condition for the development of complex life forms. The star should be between 4 and 7 billion years old. If the star is younger, evolution may not have enough time to generate intelligent beings, and if it is older, then the planets will have few heavy elements necessary for life, which are accumulated by previous generations of stars. You should choose single luminaries, since in binary systems the probability of the existence of planets with stable orbits and climatic conditions is lower. For the same reason, among stars with already discovered planets, those in which the shape of planetary orbits is close to circular are preferred. It is also desirable that from the star to which the radio message is sent, the Sun could be seen against the background of some remarkable astronomical object - a pulsar, quasar, or the center of the Galaxy. In this case, the chances of detecting our signal are increased, since it can be seen in the course of ordinary astronomical observations. Finally, one should choose stars within the “life belt” of our Galaxy - that “greenhouse” region where the speed of orbital motion around the galactic center is close to the speed of rotation of the spiral arms. In this zone (which includes the Sun), stars rarely cross the arms of the Galaxy, where violent star formation processes occur, accompanied by powerful supernova explosions,capable of interfering with the development of life.
Rendezvous blindfolded
The question of choosing the circumstances for interstellar communication is far from limited to the selection of stars, that is, the spatial directions for sending signals. There are also a number of parameters that can vary widely. These are the transmission time, the required signal power, the wavelength of the message carrier, its polarization, the modulation method, and, finally, the structure of the transmitted information.
Synchronization
It would seem that, without agreeing in advance, it is impossible to outline the optimal time for an interstellar communication session. But in reality this is not the case. A lot of events take place in the Universe, which are available for observation by all developed civilizations. Such are, for example, the outbursts of novae and supernovae. For example, at the moment when supernova radiation comes to Earth from another galaxy, you need to start broadcasting a message in the direction of stars located further in the direction of movement of its light. As the Leningrad scientist Pyotr Makovetsky showed back in 1979, such synchronization can increase the likelihood of establishing radio contact tenfold. After all, our signal will not only come to the addressees at a given moment in time - immediately after a supernova explosion, but will also come from an area not far from it, which further increases the chances of registering it.
Power
The speed of information transfer in interstellar messages cannot be very high. Each character, in the simplest case, each bit of information, must be broadcast long enough to be confidently distinguished from the background noise. The maximum speed depends on the power of the transmitter, its antenna diameter, wavelength, as well as the instrument used for receiving and the distance to it. The larger the diameter of the transmitting antenna and the shorter the radio wave, the narrower the beam is obtained, in which the signal power is concentrated, the less it is scattered. The three most powerful terrestrial installations capable of directionally sending radio signals into space are a radar telescope in Arecibo (Puerto Rico) and two planetary radars with a diameter of 70 meters: an American one in Goldstone (California) and a former Soviet one in Yevpatoria (Crimea). In recent years, only the last installation has transmitted messages. As mentioned, they were addressed to stars within 70 light years.
Suppose that a receiver with an area of one million square meters (1 km 2) operates at this distance - a project for such a radio astronomy antenna is currently being developed on Earth. In this case, the maximum data transfer rate is only 60 bits per second - a little faster than a teletype. Two American instruments are noticeably more powerful and could provide a speed of 500-1000 bits per second.
Even at the dawn of space radio communication research, it was shown that the optimal wavelength range for it is from 1 to 20 centimeters, in which, in terms of the totality of parameters, the greatest range is achieved. But how to choose a specific wavelength in this range? One idea is to build on the famous spectral hydrogen radio line observed throughout the universe at a wavelength of 21 centimeters. It cannot be transmitted directly on it, since the interstellar gas will weaken the signal. Therefore, you can change the wavelength by decreasing it, for example, by an integer number of times. But there is another, even more beautiful solution: divide the wavelength by a fundamental mathematical constant such as Pi = 3.14. or e = 2.71 … These constants (or multiples of them) should be known to any civilization, and the very fact of choosing a wavelength, say,Pi times different from the hydrogen line, will indicate the artificial nature of the signal. Pyotr Makovetsky called such a signal "a product of the mind." However, it is possible that over time, with the development of space communications, the best performance will be achieved for systems in the infrared or optical range, and then our ideas about the optimal wavelength will change.
Modulation
Searches for signals using the SETI program have been going on for almost half a century. And in most cases, the same principle is used to analyze them. The received radiation is subjected to digital spectral analysis and decomposed into millions and even billions of frequency channels. For example, in the Phoenix project of the US SETI Institute, a digital spectrum analyzer selects two billion channels with a width of 1 hertz, and each of them is checked for the presence of an artificial component. Apparently, this is the optimal system for searching for radio signals from other civilizations. But then our messages should be effectively recognized by such a receiver, that is, they should be based on a clear spectral language. This concept is known and widely used on Earth, it is called frequency modulation and is used by all FM radio stations.
Structure
Having agreed that the radio message is synthesized on the basis of the spectral approach, it is necessary to determine its structure. Changes in frequency over time may be absent, smooth (continuous) or discrete (abrupt). These three modes of transmission can be conditionally correlated with three languages: "nature", "emotions" and "logic". A universal message should be addressed to addressees in all three languages and consist of three parts. First, a fixed frequency probe is transmitted. Passing through the interstellar medium, it is distorted, but if there is intuition, the recipient will guess (for example, by detecting the frequency of the "mind product") that this is an artificial signal, and will even be able to extract from it astrophysical information about the environment on the way from the source to the receiver. With this information he can begin to decipher the other two parts of the message. The emotional part should be analog, that is, continuous frequency variations that reflect our emotional world and artistic images, just as music does. She could be prepared by people of art. And only the third part of the message should carry a discrete digital data stream, represented by the interleaving of two frequencies. This language is designed to reflect our logical constructions and formalized knowledge about ourselves and the world around us. This language is designed to reflect our logical constructions and formalized knowledge about ourselves and the world around us. This language is designed to reflect our logical constructions and formalized knowledge about ourselves and the world around us.
COSMIC SILENCE
Although the tasks of searching for and transmitting intelligent signals in the Universe are closely related to each other, it is important to understand their specifics. In the SETI program, when searching for extraterrestrial civilizations, we do not know exactly what we are looking for, but we assume that it exists in Nature. That is, a purely scientific task of detecting a signal, decoding it, extracting meaningful information from it is being solved. Everything here is exactly the same as when searching for new natural phenomena, with the only difference that what is sought is not a natural-scientific regularity, but a meaningful message, signals not of Nature, but of Reason.
In METI, signal transmission is a little different. The task is to synthesize and send such an interstellar message, the likes of which does not yet exist in Nature and which Nature could not generate. In this sense, the synthesis of messages is akin to art, the creative process of creating something new. But at the same time, the information intended for transmission must be presented as follows. so that it can be understood by any intelligent subject in the universe.
Creativity is always addressed to the public - viewers, listeners. But what's the point in creating messages to send into deep space? Even if they are accepted, we have practically no chance of knowing what impression they will make on the addressees. Here we step on the shaky ground of philosophical arguments and justifications. The mature planetary consciousness, feeling and realizing that the silence of the cosmos should horrify not only us, but also all thinking beings in the Universe, comes to the understanding that its mission is to take an all possible part in overcoming cosmic silence. However, such emotional and ethical considerations of the messianic and altruistic sense - to bring the long-awaited message to Others that they are not alone in the Universe - convince and inspire so far only a few. In such a case, there is a simpler consideration:if there are only civilizations-seekers in space and there are no civilizations-emitters, then the Universe is silent, which makes the success of searches very doubtful - there remains only the hope of detecting signals, such as our TV programs, unintentionally emitted into space. The terrestrial SETI program assumes that someone is still transmitting interstellar radio messages. And if so, then our own experiments in sending them should not cause confusion.then our own experiments in sending them should not cause confusion.then our own experiments in sending them should not cause confusion.