This year, the Search for Extra-Terrestrial Intelligence (SETI) project will be 58 years old!
On April 18, 1960, Time magazine informed readers that a young employee of the National Radio Astronomy Observatory, Frank Drake, for the first time in history, was trying to establish one-way contact with carriers of extraterrestrial intelligence. As such, he chose the hypothetical inhabitants of the equally hypothetical planetary systems of the stars Tau Ceti and Epsilon Eridani, located 12 and 10.5 light years from the Sun. Drake listened (literally with a speaker) radio waves recorded in a narrow frequency band near 1.420 GHz with an 85-foot radio telescope aimed at these stars. With the exception of a single false alarm due to radio interference from a terrestrial military source, Drake heard only static noises for four months. In August, he concluded that further attempts were futile and switched to studying (on the same equipment) the magnetic splitting of spectral lines of cosmic hydrogen, known as the Zeeman effect. Thus ended the project "Ozma", named after the princess of Oz from the wonderful fairy tale by Frank Baum. And the SETI (Search for Extraterresrial Intelligence) began.
Radio or light?
Drake began preparing his experiment in the early spring of 1959. He did not choose the receiving frequency of 1.420 GHz by chance - it emits atomic hydrogen scattered between galaxies, the most common element in the Universe. Radio waves with such a frequency are generated when an unexcited (i.e., located at the lower orbital level) electron transitions from a state when its spin is parallel to the nuclear spin to a state with a lower energy when the spins are opposite. In this case, a photon is emitted with an energy of 5.9x10-6 eV, which corresponds to the frequency chosen by Drake (or a wavelength of 21.1 cm). Not hoping to get money for just listening to interstellar signals, Drake additionally substantiated his project by studying the Zeeman effect. Interestingly, Drake's unique receiver cost only $ 2000,because the electronics firm Microwave Associates provided him with the latest parametric amplifier free of charge, one of the best in the world at the time.
Stars with planets from which one can observe the passage of the Earth across the disk of the Sun (in the plane of the ecliptic), according to scientists, - most likely candidates for sending radio signals intended for earthlings.
1959 marks another pioneering event in SETI history. In September, Cornell University professors Giuseppe Cocconi and Philip Morrison published a short note in Nature that proposed the same space communications strategy as Drake. They also considered it very likely that extraterrestrial civilizations would communicate at a wavelength of 21.1 cm and therefore recommended looking for brothers in mind in the 1.420 GHz ± 300 KHz band, covering Doppler frequency shifts caused by the movement of signal sources relative to the Earth at speeds of no more than 100 km /from. This article was the first scientific publication devoted to the SETI problem.
A year and a half later, another programmatic paper on space communications appeared in Nature, signed by Robert Schwartz and Charles Townes, the future Nobel laureate. The authors were the first to propose the use of "optical masers" (in other words, lasers - this term was not yet generally accepted). This work goes back to the strategy of searching for space signals carried by short bursts of infrared or visible light, which is now called OSETI (Optical SETI). In the same 1961, the first conference on contacts with extraterrestrial civilizations was held at the National Radio Astronomy Observatory. Drake presented there his famous formula for estimating the number of potential space contacts in our Galaxy.
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Space beacons
What will a technologically advanced civilization do to reduce the cost of communicating with space neighbors? After all, continuous transmission of signals on one or several narrow radio frequency bands is very expensive and not very promising. Therefore, the traditional search for messages on the wave of emission of intergalactic hydrogen and even in the whole water window is unlikely to be successful. It is much more profitable to send short signals in a wide frequency range of the order of 10 gigahertz. These frequencies can be generated using non-linear transmitters with compact antennas, which are immeasurably cheaper than linear systems for narrowband broadcasting. And the chances of being heard in this case are greater, since the frequencies of the strongest intragalactic radio noise are much lower.
“These considerations are at the heart of our idea of space radio beacons that send signals thousands of light years away,” says Gregory Benford, professor of astrophysics at the University of California, Irvine, who developed the concept with his twin brother James. radio physicist, and nephew Dominic, NASA employee. - Let's assume that such beacons exist and they can be caught by earthly instruments. The question arises of how to look for them and how to distinguish such signals from radio bursts caused by natural processes. This requires constant monitoring of both the northern and southern skies, as well as a spectral analysis of each suspicious radio burst. This is too exotic a task for professional radio telescopes,working in the framework of astronomical and astrophysical research programs. However, there are already hundreds of amateur radio telescopes in the world, and their number is growing rapidly. Any of these installations can be equipped with electronics to analyze non-standard radio pulses. And if amateur radio telescopes are combined into a worldwide network to search for radio beacons, something worthwhile may come out. After all, it was amateur astronomers who discovered most of the new comets and variable stars. So why don't the owners of private radio telescopes follow their example? "something worthwhile can happen. After all, it was amateur astronomers who discovered most of the new comets and variable stars. So why don't the owners of private radio telescopes follow their example? "something worthwhile can happen. After all, it was amateur astronomers who discovered most of the new comets and variable stars. So why don't the owners of private radio telescopes follow their example?"
Senators against NASA
The Ozma project has long been the only practical enterprise for establishing space communications. It was only in 1973 that the staff of the Ohio State University observatory began a similar listening to space at a frequency of 1.420 GHz using the giant stationary Big Ear radio telescope. Research, which continued until 1995, did not bring any discoveries, although it once caused a sensation. On August 15, 1977, the telescope registered a short (only 72 s), but powerful radio burst of seemingly cosmic origin. Astronomer Jerry Eman, who spotted him on a computer printout a few days later, delightedly wrote in the margin: "Wow!" This event is featured in SETI history as Wow! signal. It turned out to be one of a kind, and its nature is still controversial - enthusiasts consider it the work of an extraterrestrial civilization.
In the early 1970s, NASA became interested in space contacts. The Cyclops project was developed, providing for the creation of an integrated network of 1000-1500 small radio telescopes to hunt for space signals sent from distances of less than 1000 light-years from Earth. The program remained on paper, but contributed to the consolidation of specialists interested in this problem. The initiators of the project noted that in addition to the hydrogen frequency of 1.420 GHz, there is another marked frequency - 1.662 GHz, corresponding to the radiation of hydroxyls OH scattered in space. In addition, they recommended not to be limited to searching only at these frequencies or in a limited part of the radio spectrum (the so-called water hole), but for reliability to make it in the range from 1 to 3 GHz.
Silence of distant planets
It is easy to understand that the Earth's radio telephone itself serves as evidence of the existence of a civilization that has reached a certain level of technical development. Reasonable inhabitants of distant exoplanets will probably come to this conclusion if they register radio emission from the Earth. In the same way, humanity can find other civilizations. According to the professor of astronomy at Harvard University Avi Loeb, to solve the SETI problem it is not at all necessary to look for directed space messages, it is enough to simply scan the sky for man-made radio noise: radio equipment, - We looked at the distances at which radar signals from the American missile defense system are received,which are capable of generating isotropic radiation with a total power of 2 billion watts (in the mode of directed pulsed beams, this power is two orders of magnitude higher). And it turned out that a receiving system with the capabilities of the European network of low-frequency radio telescopes LOFAR can register such radar stations within a radius of 50-100 light years. In this region of space there are thousands and thousands of stars, some of them may have earth-like planets.some of them may have earthlike planets.some of them may have earthlike planets.
However, the question arises, what is the probability of finding brothers in mind in this way. We don't know the exact answer, but something can be modeled. British astronomers Forgan and Nichol, whose work was published in July this year, noticed that humanity is gradually switching to cable communications, which do not contribute to planetary radio noise, and reasoned that super-powerful military radars will also someday disappear. According to their estimates, the probability of accidentally detecting civilizations within a radius of 100 parsecs from the Earth, if each of them makes noise on the air for no longer than a hundred years, alas, is very small - no more than a hundred thousandth of a percent.
We have not yet detected radio noise even from relatively close civilizations, but this fact can be interpreted in many different ways. We do not know the real reasons for the radio silence of exoplanets with intelligent life."
For another couple of decades, NASA was taking small steps to search for interstellar signals, which spent about $ 50 million. In the initial phase of preparation, somewhere in 1976, the name SETI appeared. Before that, enthusiasts for catching space messages used a more pretentious version - CETI, Communications with Extraterrestrial Intelligence. Since it was risky to promise such communications, they were replaced by search.
And yet, these efforts have ended in nothing - for political reasons. The first to take up arms against SETI was influential Senator William Proxmire, fixated on the fight against the squandering of popular funds on supposedly ridiculous scientific projects. In the early 1980s, he slaughtered SETI funds and agreed to return them only at the request of the famous astronomer Carl Sagan. SETI was left alone for several years, but the following fall, rookie Senator Richard Brian decided to save taxpayers $ 12 million for this purpose, and he got his way. Interestingly, this turned out to be his only achievement in his two terms in the US Senate.
From radio to biology
“Many people think that our institute is exclusively engaged in the hunt for space messages, - said the chief astronomer SETI Institute Seth Shostak. - However, the vast majority of our employees, and there are nearly one and a half hundred of them now, are engaged in astrobiology. About ten people are involved in projects that fit the SETI acronym. I myself deal with stars from which you can observe the passage of the Earth across the disk of the Sun. If they have planets with intelligent life, then their inhabitants can synchronize their transmissions in the direction of our planet with these events. Therefore, it makes sense to turn the receiving antennas in the direction of these stars exactly when the Earth is between them and the Sun.
Now we are not looking for optical interstellar signals, but in the recent past, similar work was carried out on the 40-inch reflector of the Lik Observatory. This is a very promising area, and we hope to return to it when funding is resumed."
Currently, optical signals are being searched for at the 72-inch telescope of the Oak Ridge Observatory at Harvard University and at the 30-inch telescope at the Leyschner Observatory in Berkeley. It is focused on monitoring bright flares no longer than a nanosecond. Astronomers do not know of a single natural process capable of generating such short pulses of light that travel hundreds of light years. Therefore, it can be assumed that they are generated by a powerful laser, the beam of which is focused in the direction of the solar system using a large telescope.
With private funds
Despite the end of government subsidies, American scientists did not forget about tracking extraterrestrial civilizations. A private institute appeared in California, which still remains the center of such searches. SETI Institute was established on November 20, 1984 for research in the field of astrobiology and the search for signals from extraterrestrial civilizations. In the fall of 2007, together with the University of California at Berkeley, the institute launched an observatory designed to capture interstellar radio signals and for radio astronomy observations. The money, $ 30 million, was allocated by one of the founders of Microsoft Corporation Paul Allen, so the observatory is called the Allen Telescope Array. Now it consists of 42 six-meter radio telescopes tuned to receive signals in the 0.5-11 GHz range.
“We are analyzing radio emissions from nearly a thousand stars located within 200 light years of the Sun. In the future, we hope to increase the number of receiving antennas to 350, but there are no funds for this yet. If our plans come true, then in the next decade we will be able to scan several million stars,”says Jill Tarter, head of the space signal monitoring group, to PM. - They often ask why we still haven't found brothers in mind. It should not be forgotten that the search for cosmic civilizations began only 50 years ago, and so far only a very approximately insignificant fraction of our Galaxy has been examined. If you scoop up a glass of water from the ocean and do not find a single fish in it, you should not think that their
Jill Tarter considers it premature to send his own messages into space: “Our civilization just 500 years ago embarked on the path of global technological progress and has little to offer the Galaxy that has existed for 10 billion years. So you have to wait and grow up. A common question is whether to be wary of space invaders? I think these are unfounded fears. Interstellar travel requires technology that only mature and therefore stable civilizations can acquire. It is difficult to imagine that they rushed into distant space for slaves, treasures or natural resources."
Folk science
Every owner of a personal computer can have a hand in monitoring space signals. To do this, you just need to connect to the SETI @ home project, which was initiated by astronomers and computer scientists from the University of California at Berkeley in May 1999. The aim of the project was to try to attract personal computer users to search for traces of interstellar signals in the raw radio telescopic data stream. During the first year, more than 2 million people joined the program, and now the total number of participants exceeds 6 million. Anyone can download the BOINС software package, Berkeley Open Infrastructure for Network Computing, which provides a connection between a personal computer and the project server. In this case, the owner himself decides how his computer will take part in distributed computing - at certain hours,by prior authorization or otherwise.
“The SETI @ home project has expanded in recent years. We are receiving data from a new high-sensitivity radio telescope receiver at the Arecibo Observatory in Puerto Rico, which has increased the number of observable stars by 30 times,”explains astronomer Eric Korpela. - After digitization and archiving, the information becomes available for processing. We are interested in a 2.5 MHz band that covers the radiation frequency of cosmic atomic hydrogen at 1.420 GHz. This band is divided into 256 fragments of 9766 Hz, which are processed by the computers of the participants. During each communication session, we send about 250 kb of raw data plus 100 kb of auxiliary information. The receiving computer analyzes this task and sends the results of its execution to our server. 10 years ago, the average processing time for one job was a week,today does not exceed two hours."
So far, scientists have not found anything, but what will happen if they manage to detect a signal from brothers in mind? According to Eric, further actions are provided for by a special international protocol regulating the actions of organizations and individuals in such a situation: “In particular, they must immediately share information with specialists engaged in the search for extraterrestrial civilizations in order to conduct an expert assessment of the results. It is also necessary to notify the UN Secretary General of the incident even before informing your own government. I hope that someday we will use these rules."
Alexey Levin