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The Search For Extraterrestrial Intelligence (SETI)
содержание презентации «The Search For Extraterrestrial Intelligence (SETI).ppt»| Сл | Текст | Сл | Текст |
| 1 | The Search For Extraterrestrial | 17 | waterhole”. Alien civilizations will know |
| Intelligence (SETI). AST 309 part 2: | that these two lines are from the | ||
| Extraterrestrial Life. | dissociation products of water, whatever | ||
| 2 | The Drake Equation: N = N* fpl nhab fL | they call H and OH. Not taken too | |
| fC fT L/T. Stars? Planets? Habitable | seriously, But convenient range to strive | ||
| Origin Complex Intelligence, Lifetime | for. (Allen Telescope Array uses this | ||
| planets? of life? life? technology? of | range, and more.). OTHER ‘MAGIC” | ||
| civilization. | FREQUENCIES Some frequency based on | ||
| 3 | Another way to see what the Drake | combinations of fundamental constants of | |
| equation represents: What is the | nature? (e.g. speed of light, Planck’s | ||
| likelihood or probability that the | constant, …) The combination can be | ||
| sequence of events shown to the right will | expressed without referring to “our” units | ||
| occur, ending up with the peculiar group | (e.g. meters) ”Intergalactic” frequency | ||
| of phenomena listed at the bottom | standard based on temperature of cosmic | ||
| branching? And are there many other | background radiation? Many others have | ||
| possible branchings that we haven’t | been suggested. Too many! None in use | ||
| thought of, or are incapable (for, say, | today. | ||
| biological reasons) of imagining? | 18 | SETI projects: partial historical | |
| 4 | Intelligence, technology. | list. Ozma (1960) In 1960, radioastronomer | |
| Intelligence—If we want to communicate | Frank D. Drake, then at the National Radio | ||
| with aliens, they must have something like | Astronomy Observatory (NRAO) in Green | ||
| what we usually call “intelligence.” What | Bank, West Virginia, carried out | ||
| does this mean? Are there different | humanity's first attempt to detect | ||
| “types”? What about other animals? Other | interstellar radio transmissions. The | ||
| cultures? Especially oral tradition | stars chosen by Drake for the first SETI | ||
| cultures. Why did humans evolve such big | search were Tau Ceti and Epsilon Eridani. | ||
| brains? Why think that extraterrestrials | From April to July 1960, for six hours a | ||
| would share our forms of cognition? Factor | day, Project Ozma's 85-foot NRAO radio | ||
| in Drake equation: What is probability | telescope was tuned to the 21-centimeter | ||
| that life elsewhere develops | emission (1420 MHz) coming from cold | ||
| “intelligence”? Call it fI . | hydrogen gas in interstellar space. A | ||
| Communication, technology—If we want | single 100 Hz channel receiver scanned 400 | ||
| signals, the aliens must have some kind of | kHz of bandwidth. The astronomers scanned | ||
| system of representation, like a language. | the tapes for a repeated series of | ||
| How likely? Other forms? Musical? | uniformly patterned pulses that would | ||
| Unimaginable? And no matter what kind of | indicate an intelligent message or a | ||
| language they have, they have to be | series of prime numbers such as 1, 2, 3, 5 | ||
| technological civilizations if they are to | or 7. With the exception of an early false | ||
| send signals across the Galaxy. We could | alarm caused by a secret military | ||
| enter these topics as two more | experiment, the only sound that came from | ||
| probabilities, fC fT . N(planets with life | the loudspeaker was static and no | ||
| that also developed intelligence and | meaningful bumps superimposed themselves | ||
| technology) = N* fpl nhab fL fC fT. | on the formless wiggles on the recording | ||
| 5 | Lifetime of the communicating phase. | paper. | |
| We left out one crucial factor: The | 19 | Arecibo: message sent to M13 (1974): | |
| fraction of the Galaxy’s age T that a | Globular cluster ~25,000 lyr away Message | ||
| civilization is in the technologically | written by Drake, Sagan, et al. Frequency: | ||
| communicating phase. We know the age of | 2380 MHz 1679 binary digits. SETI | ||
| our Galaxy is T ~ 10 billion years. | projects: partial historical list. | ||
| Consider our chances if civilizations only | 20 | Ohio State University SETI (1977-1997) | |
| last for 100 years… Average length of time | With the Big Ear fixed radiotelescope | ||
| spent in the communicating phase L. | (used Earth’s rotation to scan the sky) | ||
| Sometimes referred to as lifetime of a | August 15, 1977: detected a strong | ||
| technological civilization. Call it L. Our | narrow-band signal for 72 secs: SETI | ||
| final Drake equation is then: N = N* fpl | projects: partial historical list. | ||
| nhab fL fC fT (L/age of Galaxy) This | Duration consistent with extraterrestrial | ||
| represents the number of communicating | source Strength: 30 times above background | ||
| civilizations in our Galaxy. We have been | noise Frequency: 1420 MHz (neutral H) | ||
| “this way” for only ~ 100 yr. If this were | Bandwidth: <10 kHz. | ||
| L, then N (number of civilizations for | 21 | SETI projects: partial historical | |
| communication in our Galaxy) would be | list. The location of the signal in the | ||
| around 1. Even if N ~ 100, there is no | constellation Sagittarius, near the Chi | ||
| hope for two way communication, and | Sagittarii star group. RA= 19h25m31s ± 10s | ||
| probably very difficult to locate them | or 19h28m22s ± 10s declination= ?26°57? ± | ||
| among a 100 billion possibilities. And too | 20? There were ~50 follow-up searches | ||
| far for biosignatures. In order for our | performed in this area, but nada => | ||
| Drake equation “N” to come out reasonably | Origin of the Wow! signal is still | ||
| large (say a million), the average | undetermined. | ||
| lifetime L must be extremely large, | 22 | SETI projects: partial historical | |
| something like 100,000 to a million years. | list. NASA asks for SETI proposal, | ||
| ? This means we can expect any nearby | astronomers propose “Project Cyclops”, | ||
| civilizations to have had a long lifetime, | 1000 100 meter radio telescopes on back | ||
| i.e. be very advanced. I think this is the | side of moon, costing $10 billion (1970s). | ||
| only thing we can know with any certainty | NASA asks for more moderate plan, planning | ||
| about extraterrestrial civilizations: If | for next ~ 17 years. Ohio State SETI: | ||
| there are enough of them to make it likely | 1977-1997 (replaced by golf course). Best | ||
| we will find them, then they must be very | known for the “wow” signal. Harvard, Paul | ||
| advanced (using beacons)! | Horowitz and Project META (millions of | ||
| 6 | SETI web sites. SETI at Space.com | bands in frequency), Project BETA (billion | |
| http://www.space.com/searchforlife/index.h | bands in frequency). Horowitz and Sagan | ||
| ml SpaceRef.com | 1993 Astrophysical Journal summarize | ||
| http://www.spaceref.com/Directory/Astrobio | results. One of first SETI papers in | ||
| ogy_and_Life_Science/seti/ Ongoing SETI | refereed journal. Harvard and Horowitz now | ||
| searches: SETI Institute/Allen Telescope | converted to Optical SETI, largest in | ||
| Array http://www.seti.org/ Project | world. UC Berkeley’s Project SERENDIP. | ||
| SERENDIP, UC Berkeley | Since 1977! Part of data analyzed by 5 | ||
| http://seti.ssl.berkeley.edu/serendip/sere | million home computers through SETI@home. | ||
| dip.html SETI@home | Dec. 1991. NASA funds $100 million SETI | ||
| http://setiathome.berkeley.edu/ Sourthern | effort (“MOP”). Detailed plan for combined | ||
| SERENDIP, Univ. Western Syndey | targeted and sky survey searches. 1993: | ||
| http://seti.uws.edu.au/ SETI Italia | Funding removed by senate amendment | ||
| http://www.seti-italia.cnr.it/ Optical | Project Phoenix (SETI Institute) rises | ||
| SETI at Berkeley | from the ashes. Piggy-backs off various | ||
| http://seti.ssl.berkeley.edu/opticalseti/ | radio telescopes, mainly Arecibo. 2001: | ||
| Harvard http://seti.harvard.edu/oseti/ | Paul Allan and others fund the Allen | ||
| Amateur SETI: Project BAMBI | Telescope Array, 350 6meter telescopes. 42 | ||
| http://www.bambi.net/ SETI League | complete by Oct. 2007. | ||
| http://www.setileague.org/ Project ARGUS | 23 | SERENDIP. One of oldest operational | |
| http://www.setileague.org/argus/index.html | SETI searches--since 1979, UC Berkeley. | ||
| 7 | STRATEGIES FOR COMMUNICATION WITH | 1997--installed as piggyback at Arecibo | |
| EXTRATERRESTRIAL CIVILIZATIONS. ?SETI is | radio observatory (picture below), largest | ||
| concerned with searches for signals from | single-dish radio telescope in world (but | ||
| extraterrestrial civilizations, not | can only point in one direction). SERENDIP | ||
| spectral “biomarkers” we discussed earlier | = Search for Extraterrestrial Radio | ||
| in course, or actual travel to other star | Emissions from Nearby Developed | ||
| systems. ? Except for 1974 signal to | Intelligence Populations. SERENDIP IV is | ||
| globular cluster M13 (thousands of light | the fourth instrument of the project, | ||
| years away), we only try for reception, no | collects data by 'piggybacking' on top of | ||
| transmission. (“What if they are all | the Arecibo radio telescope. SERENDIP IV | ||
| listening?”) ? “Signals” could be | instrument is basically a 200 billion | ||
| intentional (they are trying for contact) | operations per second supercomputer that | ||
| or nonintentional (we eavesdrop, one way | scans 168 million narrow (0.6 Hz) channels | ||
| or another). A few unintentional | every 1.7 seconds for signals that are | ||
| candidates listed on next slides, but we | significantly 'louder' than the background | ||
| are most concerned with intentional | static. Some of its data is analyzed | ||
| signals, and with establishing a two-way | through SETI@home for desktop | ||
| conversation. ? Remember: Distance to even | computers--so far millions of users, | ||
| the nearest 1000 or so stars ~ 50 light | largest distributed computing project in | ||
| years, and we expect only a tiny fraction | world, led to ~ 100 other distributed | ||
| of them to have life, let alone | computing projects, e.g. folding@home, | ||
| intelligent communicating life, so we are | prime@home, climatenet@home, … (details on | ||
| necessarily asking whether to undertake a | next slide). The Arecibo radio telescope | ||
| search with a guaranteed very low | in Puerto Rico, used by both SETI Insitute | ||
| probability of success, and, even if | for Project Phoenix, and by UC Berkeley | ||
| successful, communications will involve | for their SERENDIP IV. | ||
| decades or even centuries. You can see why | 24 | SETI@home: Now searching for pulses. | |
| funding for SETI is sparse! | August 2008: SETI@home switches to search | ||
| 8 | Four types of nonintentional types of | for pulsed radio signals. Observations are | |
| signals: Leakage radiation from radio, TV, | from SERENDIP piggy-backed on radio | ||
| or other radio broadcasts. Earth as | telescope at Arecibo that is built into a | ||
| example: Many TV stations broadcasting | mountain. This dish only points in one | ||
| different shows, or same shows at | direction as sky drifts across this | ||
| different times, radio waves emanating | direction--the drift takes about 12 | ||
| from Earth have always been incoherent, | seconds for a given point in the sky. | ||
| completely scrambled. It is not true that | SETI@home searches for signals that rise | ||
| alien ETI could be seeing our early TV | and fall in 12 seconds--any object will do | ||
| shows! Alien communications, e.g. between | this, but most will be broad-band sources | ||
| home planet and colonies. We would have to | (top image). Narrow search by requiring | ||
| be almost exactly in the line of sight | narrowband signal (2nd image). Will check | ||
| between home planet and colony, and guess | for several different bandwidths. | ||
| the frequency range. Seems very unlikely. | Information in image? Search for pulsed | ||
| Dyson spheres -- hypothetical constructs | signal (3rd image). If from planetary | ||
| built by advanced civilizations in order | system, should also be Doppler shifting | ||
| to collect nearly all the energy of their | (“chirped” signal), as in 4th image. Home | ||
| parent star. Spherical shell at same | computers look for various combinations of | ||
| distance from star as the home planet. The | frequencies, bandwidths, and chirp rates. | ||
| intercepted energy is somehow channeled to | See if you can understand why the white | ||
| planet. But shell is heated by the | “thing” in the illustration below might be | ||
| incident radiation: What will its | a signal… SETI@home screensaver Can you | ||
| temperature be? At what wavelength would | see the alien signal?? | ||
| you conduct a search for Dyson spheres? | 25 | SETI@home and distributed computing. | |
| Products of technological activity – e.g. | By 2007 over 40 projects had joined the | ||
| gamma rays from their (hypothetical) | BOING distributed computing family, using | ||
| fusion propulsion systems, … CFC molecules | the software provided by SETI@home. | ||
| from their air conditioners… | Protein folding: folding@home, | ||
| 9 | TV leakage radiation. World TV | predictor@home, Rosetta@home, | |
| spectrum. World TV power vs. time. | Proteins@home Primegrid.com: privately run | ||
| 10 | Geographical distribution of TV | mathematical project that searches for | |
| stations. Geographical distribution of TV | very large prime numbers and has already | ||
| stations. As Earth rotates, this “pattern | found more than 100 new primes. | ||
| of populated areas” is the only evidence | Einstein@home is based at the University | ||
| for TV broadcasts. | of Wisconsin in Milwaukee and searches for | ||
| 11 | How would an alien civilization try to | pulsars in the sky based on data from the | |
| communicate across many light years of | gravitational wave detectors LIGO and GEO. | ||
| space? The only thing that is almost | climateprediction.net: Oxford Univ. UK | ||
| certain is that they will use | high-profile climate simulator. Jan 2005: | ||
| photons—fastest and cheapest way to | First paper in Nature, 2,570 simulations | ||
| transmit information that exists (as far | of Earth. By 2007: 50,000 simulations. | ||
| as we know). Even though photon signals | Goal is several million, to explore 23 | ||
| are the only choice we can think of, that | parameters of the climate model. | ||
| still leaves many considerations that we | 26 | Allen Telescope Array (ATA). | |
| need to guess about: Where to point our | Eventually 350 6 meter antennas, | ||
| telescopes? What kind of stars should we | equivalent to 100 meter single dish. 42 | ||
| point our telescopes toward? Or would it | dishes saw “first light” in Oct 2007. | ||
| be better to survey the whole sky? | Entered hibernation due to funding | ||
| Wavelength: What wavelength region should | problems this year! => Maybe restart in | ||
| we expect is optimum for sending | Sep 2011 due to private donations > | ||
| interstellar signals? Radio? Optical? | $200,000 Unique features: ? Large field of | ||
| Other? Bandwidth: What range of | view, so can scan sky faster in survey | ||
| wavelengths? Broadband or narrow-band? | mode. ? Large range of frequencies (1-10 | ||
| WHY? Recognition and Interpretation: How | GHz for targeted search, five times range | ||
| would a message, or some sign that it is | of Phoenix), and small bandwidth (~ 1Hz), | ||
| not a natural phenomenon, be | using more than a billion channels. ? | ||
| distinguished, and how would a meaningful | Finally offers SETI 24/7 monitoring | ||
| message be encoded? We’ll discuss each of | (Phoenix had Arecibo for only about 3 | ||
| these in turn. | weeks per year 1998-2004) Goals: ? | ||
| 12 | WHERE TO POINT? a. Sky survey. Survey | Targeted search: Survey 106 stars with | |
| entire sky with telescope’s “beam” – this | good sensitivity between 1 and 10 GHz for | ||
| might involve millions of directions for | weak non-natural transmitters. ? Sky | ||
| typical radio telescopes. If you want to | Survey ~ monitors inner Galactic plane in | ||
| finish in your lifetime, you could only | “water hole” range 1420-1720 MHz for very | ||
| spend a very brief time on each direction, | strong non-natural transmitters. | ||
| so you could only detect very strong | 27 | Optical SETI (OSETI). When faced with | |
| signals. But at least you won’t miss any | the question “What kind of signals would | ||
| of them. And the method doesn’t make any | alien civilizations transmit, the | ||
| assumptions about what the most likely | traditional answer has been: Continuous | ||
| stars are for signal reception. ? This is | narrow-band radio transmissions An | ||
| a low-sensitivity method, but complete for | alternative: Maybe they would send | ||
| strong signals. b. Targeted search. Point | distinct broad-band pulses. They would | ||
| at the nearest (less than about 50 to 1000 | stand out against background noise not | ||
| l.y.) stars roughly like the sun and | because they are precisely centered on a | ||
| cooler (recall conditions for habitable | particular wavelength, but because they | ||
| planets). Could detect weaker signals, | are very short and punctuated bursts of | ||
| i.e. would have higher sensitivity. But | energy—unlike most other natural | ||
| you will only cover a tiny fraction of the | phenomena. This is the world of Optical | ||
| sky. ? This is a high-sensitivity method, | SETI, which searches for signal in the | ||
| but severely incomplete. Most current | visible (or infrared in future) light | ||
| searches have shifted to a sky survey mode | range, usually looking for nanosecond | ||
| (a) However plans change rapidly—the Allen | pulsed laser radiation. Reasons: Radio | ||
| Telescope Array (largest current project) | 21cm line has huge noise problem with | ||
| combines both approaches. And some | interstellar gas. Laser-like signals are | ||
| “optical SETI” searches (see below) are | tightly beamed, so can be sent over very | ||
| targeted searches. | large distances (no loss due to | ||
| 13 | What frequency should be used to | inverse-square law). With current | |
| listen or send interstellar messages? From | equipment can send out pulsed laser beam | ||
| the Earth’s surface, most radiation is | 5000 times brighter than the Sun | ||
| blocked by the atmosphere. The exceptions | Unidirectional--can pinpoint direction | ||
| are optical (visual) and radio photons. | with high precision. Higher frequency | ||
| Earth’s atmosphere also blocks out most of | --can encode more information. There are | ||
| the infrared part of the spectrum due to | two OSETI programs at UC Berkeley, and now | ||
| water vapor in our atmosphere. From the | ongoing or about-to-launch OSETI searches | ||
| highest mountains or a jet plane, the | at Harvard, Lick Observatory, and Columbus | ||
| infrared is barely accessible, but not for | Observatory. Current projects: Berkeley: | ||
| the continuous kinds of surveys we have in | Monitors 2500 stars as part of exoplanet | ||
| mind. Note that if we could do such a | search. Searches for ultra-narrow band | ||
| survey from Earth orbit (expensive), or, | signals. Harvard: since 1998, using 61 | ||
| if we only had about $100 billion dollars | inch telescope. Nearly 100,000 | ||
| so that we could build a facility for SETI | observations. Dec. 2000: new 72 inch | ||
| on the far side of the moon (“Project | telescope dedicated to an all-sky survey. | ||
| Cyclops”), our considerations might be | Can detect nanosecond (billionth of a | ||
| different. Why have most SETI searches | second) pulses and cover entire sky in 200 | ||
| concentrated on radio wavelengths instead | nights. Lick Observatory Targeted search | ||
| of optical? A single amazingly influential | began in 2000. First results published in | ||
| paper by Cocconi and Morrison (1960 | Stone et al. 2005 Astrobiology. 14 | ||
| Nature) set the stage. Their arguments for | candidate events. | ||
| radio SETI are on next slide. | 28 | Encoding a message. ?SETI researchers | |
| 14 | Reasons for radio SETI: 1. | focus on a signal anyone could comprehend. | |
| Interstellar dust selectively blocks | Not clear this is sensible! ? It is very | ||
| shorter wavelengths (higher frequencies) | sensible to expect digital, binary, not | ||
| strongly suggests we use the IR or radio | analogue signal. ? How to encode a picture | ||
| parts of the spectrum (long wavelengths or | into a string of binary (0,1) signals? The | ||
| small frequencies). But IR is dominated by | simplest and most efficient way to encode | ||
| Earth’s atmospheric molecular emission if | a message (we think) is binary code. Use | ||
| search from surface, so that leaves radio. | only 2 characters, e.g. a 1 and a 0, or a | ||
| Notice that radio SETI allows reception | + and a - , or "on" and | ||
| from the entire galaxy, but optical isn’t | "off", ... Each 1 or 0 (or | ||
| that bad, since we can see stars out to ~ | whatever) is a "bit". Then the | ||
| 1 kpc. Besides, most radio searches are | message can just be sent as a series of | ||
| concentrating on nearby stars anyway. (We | pulses. Expect the message to be a | ||
| don’t want 1000-year “conversations.”) 2. | two-dimensional picture that is encoded in | ||
| Radio photons are cheaper to send than | a one-dimensional binary string that | ||
| optical photons (because energies are ~ | factors into prime numbers. e.g. 551 = 29 | ||
| 100,000 times smaller for radio). 3. The | x 19 (or 19 x 29); 1679 = 23 x 73 (the | ||
| main consideration is noise: Here “noise” | 1974 Arecibo transmission). Example: We | ||
| means anything that is not an alien | receive signal 1111100000101011010110101. | ||
| signal--any kind of interference. We | This factors into 5 x 5, giving a picture | ||
| should listen (or send) where the noise is | of the greek letter "pi". Or try | ||
| minimized, so that we can recognize the | the letter "E", etc. But why | ||
| (probably weak) signal. Noise is minimum | would ETI send out signals that anyone | ||
| in a region of the radio part of the | could decode? Perhaps they send out | ||
| spectrum. This is summarized in a classic | signals which could be understood only by | ||
| graph shown on next slide. Arecibo Home of | others who are already "at the same | ||
| SERENDIP, SETI@home, Phoenix. Allen | level" as they are. What would be a | ||
| Telescope Array, SETI Institute, N. Calif. | difficult signal for us to recognize? | ||
| 15 | Alien signaling: Choosing a wavelength | Maybe the test would be to recognize some | |
| range that minimizes “noise” -- anything | sort of "meaning" in the | ||
| that is not an alien signal. Avoid very | message. (Think about musical signals. At | ||
| low frequencies (wavelengths too large), | present, there is no viable theory of | ||
| because synchrotron radiation from | musical meaning in music analysis, | ||
| supernova remnants dominates there. (Far | philosophy, cognitive science, pattern | ||
| left in figure) Avoid frequencies higher | recognition, or any other field that has | ||
| than about 10 GHz because of H2O and O2 | approached the problem.) Deeper questions: | ||
| emission from Earth’s atmosphere. Cosmic | Will symbolic communication systems be | ||
| microwave background radiation sets | universal among intelligent creatures? Is | ||
| “floor” at intermediate frequencies, and | “grammaticity” hard-wired into our brains? | ||
| that is where the noise is minimum, and | Another example of single mutation? | ||
| where we should search. A message will | 29 | The Eerie Silence….. ? SETI has been | |
| arrive in a narrow wavelength band or | on-going for about 50 years and NOTHING | ||
| bands, not spread over the whole 1-10 GHz | has been detected ? Conclusion: are we | ||
| region. There are 10 billion 1 Hz bands in | alone? Are there no ETIs in our galaxy? ? | ||
| this range. How to decide which ones to | No, not yet. But they are probably no | ||
| pick? First, must understand bandwidth. | nearby ETIs similar to us, nor a nearby | ||
| 16 | The importance of bandwidth. Basic | strong radio beacon intended to notify us | |
| idea: Can pack more power in a narrow | of ETI’s presence. There are many stars | ||
| frequency range (narrowband signal) than | not observed yet, so many frequencies not | ||
| spreading out over a large range | explored and many other possible ways for | ||
| (broadband signal). So can distinguish a | ETIs to communicate. | ||
| narrowband signal from the background more | 30 | What IF The Eerie Silence is broken! | |
| easily. Think of the everyday radio | What then? There is actually a so-called | ||
| analogy again, and it should be clear! | “SETI Post Detection Task Group” (a | ||
| SETI@home: Each vertical “band” is a 10 | permanent study group of the International | ||
| kHz “slice” of the 2.5 MHz wide SERENDIP | Academy of Astronautics). It’s only a | ||
| data. There are 250 such “slices.” But | think tank, no legal status, no | ||
| search is for signals much narrower than | governmental involvement. In case a signal | ||
| these bands. | is detected the task group would advise to | ||
| 17 | Which frequency? If it is true that | perform the following steps: Verify | |
| narrow-band signal is the only sensible | authenticity of ETI signal Contact the | ||
| approach, how will we decide which band to | International Astronomical Union => | ||
| use? Suggested “beacon frequencies” (or | which will contact UN. inform the | ||
| “hailing frequencies” or “magic | government of the country (countries) | ||
| frequencies”): HI (neutral hydrogen) 21cm | where radio telescope is located Public | ||
| (wavelength) line? The frequency is 1420 | announcement Such a discovery will have | ||
| Megahertz = 1.42GHz Natural, abundant, but | unprecedented and enormous scientific, | ||
| lots of interference by interstellar gas. | social, cultural, political and spiritual | ||
| (Latter has apparently been forgotten.) OH | consequences for humanity. Nobody knows | ||
| line at 1.7 GHz? H + OH = H2O, so maybe | what will happen (depends on nature of | ||
| region between these two --> “the | signal, e.g. distance to source). | ||
| The Search For Extraterrestrial Intelligence (SETI).ppt | |||
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The Search For Extraterrestrial Intelligence (SETI)
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«The green movement» - Management of each such branch in which head there is a chief executive, carries out national board. "Green" movement in the world. One of the largest victories гринписовцев in the given campaign can name refusal of flooding of an oil platform brent spar as it contained many toxic substances.
«The english-speaking countries» - Scotland. USA. Australia. The English-speaking countries. Great Britain. Disneyland.
«Языковые лагеря» - Языковые лагеря. Языковые лагеря в России и за рубежом. Распорядок дня. Москва. Knowledge control. Тематические вечеринки. English lessons. E-Camp explore Europe. Елочки. Workshops. Искра.
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