When astronaut Neil Armstrong took that small step on the Moon on 20 July 1969, it was indeed a giant leap for all mankind. After the Apollo 11 lunar explorers’ return to earth, the then American President Richard Nixon went so far as to say, “This is the greatest week in the history of the world since Creation”. This must have sounded like music to the ears of the creationists and their descendants, the intelligent design theorists, in the western world who visualize human life on earth as just a week’s handiwork performed by a super intelligent being. Nature of course has been far less enterprising and taken millions of years to do the job through a long drawn out and complex evolutionary process. Nixon may or may not have used the term ‘creation’ in its biblical sense, but he was not far off the mark if he implied that the event was the greatest since human life itself took firm root on planet earth, whenever this may have been. To celebrate the next such momentous event in history we may have to wait until one of the most tantalizing questions of all time facing human civilization is answered definitively – is there intelligent life elsewhere in the universe? If and when this is answered in the affirmative, an even more momentous event would be the establishment of contact with such intelligent life. It could indeed be a tremendously long wait and very far into the future.
Since time immemorial, mankind has been fascinated by the possibility of intelligent life outside our planet earth. While there has been no credible factual evidence of any kind whatever even up to the present day, writers of science fiction, movie makers and the modern media have given themselves unfettered liberties and let their imaginations run riot. If their claims are to be believed, the earth is crawling with a plethora of uninvited extraterrestrial aliens deposited by UFOs (Unidentified Flying Objects) flying all around us, whose favorite pastime seems to be abducting or at least frightening hapless innocent earthlings! Ufology has become nearly as popular as, but no more scientific than, Astrology.
With the discovery of innumerable stars having physical properties and chemical composition similar to that of our Sun in the last two centuries, wild imagination has given way to meaningful speculation about extraterrestrial life, including intelligent life as prevalent on earth. It makes eminent scientific sense to expect at least a tiny fraction of these stars to have an earth-like planet with similar life forms, including intelligent life.
In the latter half of the twentieth century, scientists decided that the best way to approach the problem would be to scan the skies and ‘listen’ for non-random patterns of electromagnetic emissions such as radio or TV waves in order to detect another possible civilization somewhere else in the universe. This is the essence of the ongoing worldwide SETI (Search for Extraterrestrial Intelligence) effort.
Radio is believed by most scientists to be the best means we have for interstellar communication, considering the vast distances involved. Radio waves, like all electromagnetic radiation, travel at the speed of light – 300,000 kilometers per second. This is the fastest velocity possible, and yet even Proxima Centauri, the closest star to our own Sun, is so far away that light takes approximately four years to make the journey. In contrast to the speed of light, a typical fast spacecraft we have with current technology travels about 15 kilometers per second. At such speeds, it would take a spaceship about 80,000 years to reach our nearest neighbor! In other words, interstellar travel by earthlings is virtually impossible for the foreseeable future even within our own galaxy. We have to look for other, indirect, means to look for evidence of intelligent life elsewhere in our galaxy.
Radio waves are thought to be the optimum band of the electromagnetic spectrum for interstellar communication because they are relatively free of the absorption and noise associated with other areas of the spectrum. Radio, visible light, and the near infrared are the only electromagnetic radiations able to penetrate the earth's atmosphere, and of the three, radio is not as easily absorbed by interstellar gas and dust. In addition, stars are generally ‘quiet’ in the radio frequencies. This makes radio a natural candidate for a ‘beacon’ by an advanced civilization, or for interstellar communication between such civilizations.
In late 1959 and early 1960, the modern Radio-SETI era began when Frank Drake conducted the first such SETI search at approximately the same time that Philip Morrison and Giuseppe Cocconi published a key journal article suggesting this approach.
Project OZMA was the first systematic attempt to detect artificial radio signals from nearby stars. Named after the princess in Frank Baum's Wizard of Oz, it was the brainchild of American radio astronomer Frank Drake working at the Green Bank observatory in West Virginia, USA. Drake began preparations for Ozma in 1959, the same year in which the seminal theoretical paper on SETI by Philip Morrison and Guiseppe Cocconi was published in the British journal Nature. These developments, although occurring more or less simultaneously, were quite independent of each other. However, both concluded that the best chance of success would come from searching at a radio frequency of 1,420 MHz (corresponding to a wavelength of 21.1 cm) since the 21-centimeter line of neutral hydrogen in the Galaxy might represent a natural wavelength at which intelligent species would try to communicate. Although, after 150 hours of ‘listening’ from two nearby stars the effort proved futile, it was to be the forerunner for many more, increasingly sophisticated, searches which continue to this day at ever increasing pace.
Project SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) was the first major organized large scale effort, begun in 1979. It underwent further stages of improvement. SERENDIP IV consisted of 40 spectrum analyzers working in parallel to look at 168 million narrow (0.6Hz) radio frequency channels every 1.7 seconds. It was effectively a 200 billion-instructions-per-second supercomputer. The equipment was installed piggyback, without affecting the primary work of the facility in any way, at the 1000-foot non-moving Arecibo National Radio Telescope Observatory – the largest radio telescope in the world – in Puerto Rico, USA, and managed by the University of California at Berkeley. SERENDIP V, the most recent version of the project, began in 2009. It employs a two billion channel digital spectrometer covering 300 MHz of bandwidth.
Most of the SETI programmes in existence today require fast computers that can analyze data received from the telescope in real time. None of these computers look very deeply at the data for weak signals nor do they look for a large class of signal types. This is due to the limitation on the amount of computer power available for data analysis. To probe into the weakest signals, a greatly enhanced amount of computer power is necessary. It would take a monstrous supercomputer to get the job done. SETI programmes cannot afford to build or buy that computing power. There is a trade-off that they can make. Rather than a huge computer to do the job, they could use a smaller computer but take longer to do it. But then there would be lots of data piling up. What if they used a huge number of small computers, all working simultaneously on different parts of the database? Where can the SETI team possibly find thousands of computers they would need to analyze the data continuously streaming from the Arecibo Radio Telescope?
There are already hundreds of thousands of computers that are available for use, owned by individuals and institutions all over the world. Most of these computers sit around most of the time accomplishing absolutely nothing and wasting electricity as well. This is where SETI@home comes into the picture. The SETI@home project harnesses the potential of such computers to get its job done. It has built up a huge network of computers whose services are being volunteered by millions of users all over the world. The user software can be run either exclusively during the idle time of a computer or continuously as an additional task while being used for other purposes as well (multi-tasking). Most serious volunteers prefer the latter.
The SETI data analysis task can be easily broken up into little pieces that can all be worked on separately and in parallel. None of the pieces depends on the other pieces. Of course, there is only a finite amount of sky that can be seen from Arecibo through the fixed telescope. In the last two decades the entire sky as seen from the telescope has been scanned several times.
Breaking up the Data
Data are recorded on high-density tapes at the Arecibo telescope in Puerto Rico and sent to Berkeley. They are then divided into 0.25 MByte chunks (which are called ‘work-units’). These are sent from the SETI@Home server over the Internet to volunteers around the world to analyze. There are nearly 3 million such actively participating volunteers worldwide.
SETI@home looks at a width of 2.5 MHz of data, centered at 1,420 MHz. This is still too broad a spectrum to send to any one volunteer for analysis, so this spectrum space is broken up into 256 pieces, each 10 kHz wide. These 10 kHz pieces are now more manageable in size. The SETI computer sends out about 107 seconds of this 10 kHz data in the form of a ‘work-unit.’
Sending the Data
SETI@home connects to the volunteer’s computer via the Internet when transferring data. This occurs only when the computer has finished analyzing a work-unit and wants to send back the results (and get another work-unit). The data transmission lasts just a few seconds with most common modems and disconnects immediately after all data is transferred.
The SETI staff keeps track of the work-units in the Berkeley campus of the University of California with a huge database. When the work-units are returned to them, they are merged back into the database and marked ‘done.’ Their computers look for a new work-unit for the volunteers to process and send it out, marking it ‘in progress’ in the database.
What SETI@home looks for
The easiest way to answer this question is to ask what we expect extraterrestrials to send. We expect that they would want to send us a signal in the most efficient manner for them that would allow us to easily detect the message. Now, it turns out that sending a message on many frequencies is not efficient. It takes lots of power. If one concentrates the power of the message into a very narrow frequency range (narrow bandwidth) the signal is easier to weed out from the background noise. This is especially important since we assume that they are so far away that their signal will be extremely weak by the time it gets to us. So, we're not looking for a broadband signal (spread over many frequencies); instead, we are looking for a very specific frequency message. The SETI@home screen saver program that displays the work in progress on the volunteer’s computer monitor acts like tuning a radio set to various channels, and looking at the signal strength meter. If the strength meter goes up, that gets our attention.
Another factor that helps reject local (earth-based and satellite-based) signals is that local sources are more or less constant. They maintain their intensity over time. On the other hand, the Arecibo telescope is fixed in position. So the sky "drifts" past the focus of the telescope. It typically takes about 12 seconds for a target to cross the focus (or ‘target beam’) of the dish. We therefore expect an extraterrestrial signal to get louder and then weaker over a 12 second period. We are looking for this 12 second ‘Gaussian’ signal within the 107 seconds of data. We can also expect the signals to be pulsed since this would be a very efficient means of coding information.
Because of the rotational motion of the planets, both ours and ‘theirs’, there is likely to be a ‘doppler shifting’ or changing frequency, of the signal because of our relative motions. This might cause the signal to rise or fall in frequency slightly over the 12 seconds. These are called ‘chirped’ signals. In summary, we look for ‘chirped’ and ‘pulsed’ signals as indicated in the adjacent graph.
Signals that show a strong power at some particular combination of frequency, bandwidth and chirp are subjected to a test for terrestrial interference. Only if the power rises and then falls over a 12 second period (the time it takes the telescope to pass a spot in the sky) can the signal be tentatively considered extra-terrestrial in nature. Spikes (short radio bursts) above a threshold value, doublets and triplets are also recorded.
Depending on how the telescope was moving when the work unit was recorded, the computer will do between 2.4 trillion and 3.8 trillion mathematical operations (flops or floating point operations) to complete its work. Depending on how powerful the volunteer’s computer is, the time taken for processing one full work unit may range from 3 to 50 hours! These calculations include a fast Fourier transformation of the signal data to yield a frequency spectrum.
The initial software platform, now referred to as "SETI@home Classic", ran from May 1999 to December 2005. This program was only capable of running SETI@home. It was later merged with BOINC (Berkeley Open Infrastructure for Network Computing), which also allows users to contribute to other distributed computing projects at the same time as running SETI@home. The more versatile BOINC platform (called SETI@home II) allows testing for additional types of radio signals. Also, it covers an enhanced bandwidth of 50 MHz over 700 million channels.
Project Phoenix is a complimentary SETI project involving the analysis of patterns in extraterrestrial radio signals. It is run by the independently funded SETI Institute of Mountain View, California, USA. It started work in February 1995 with the Parkes radio telescope located in New South Wales, Australia, the largest telescope in the southern hemisphere. Between September 1996 and April 1998, the Project used the National Radio Astronomy Observatory in Green Bank, West Virginia, USA.
Rather than attempting to scan the whole sky for messages, this Project concentrates on nearby systems that are similar to our own (i.e., those most likely to have planets capable of supporting life). It has concentrated on about 800 stars within a 200 light-year range.
The Project searches for radio signals as narrow as 1 Hz between 1,000 and 3,000 MHz, a broader bandwidth compared with the conventional SETI searches.
In March 2004 the Project announced that after checking the 800 stars on its list, it had failed to find any evidence of extraterrestrial signals. This may possibly mean that our solar system is located in a rather ‘quiet’ neighborhood.
In the Radio SETI@home project, the signals are assumed to be transmitted isotropically from the source, with just a tiny fraction of it being intercepted by earth based instruments. The Optical SETI@berkeley project, initiated in 1997, is based on the assumption that a distant civilization might take recourse to sending highly focused pulses deliberately towards our solar system (This implies that it has already identified us as a potential intelligent civilization). Such nanosecond-scale optical (laser) pulses are not known to originate naturally from any astronomical source. The idea of looking for pulses in the optical band of the electromagnetic spectrum was suggested as far back as 1961 by Townes (a co-inventor of the LASER and Physics Nobel laureate) and Schwartz.
The optical pulse search employs a 30-inch automated telescope equipped with a super sensitive photometer system located at a University of California campus near Berkeley.
Advertising our presence
Our attempts to discover ETI should be complimented by efforts to announce our own existence in the solar system to nearby systems that may be harboring extraterrestrial intelligence. The first such attempt was due to Carl Sagan who persuaded NASA to include a plaque specially designed by him as part of the Pioneer deep space probes launched in 1972 and 1973. The plaque shown here carries a coded pictorial message giving some basic information about ourselves and the planet we live in. A much more complex and detailed message was included in the Voyager spacecraft launched in 1977. It was in the form of a golden phonograph record containing sounds and images portraying the diversity of life and culture on earth.
The probability of a space faring civilization discovering and intercepting these messages is so ridiculously small that these efforts can only be viewed as symbolic gestures. A more productive venture would be to send very strong radio signals or laser beams carrying coded information much the same way that we expect other ETIs to communicate with us. This has been done in recent years though not in a very organized and systematic manner. In any case, much of the radio and TV signals generated on the earth have leaked out into interstellar space over the last 60-70 years though the strengths of these signals are far too weak compared to what we ourselves expect from ETIs.
One inherent assumption in any SETI effort is that the communicating civilizations must be sufficiently advanced to have mastered the technology of radio or other electromagnetic wave communications. Obviously, if and when we discover such signals, the farther the location of the source the more technically advanced is the civilization we have to deal with. It will almost certainly be far more advanced than we are on earth. After all, our communicative capabilities are less than a century old. We are only like a new born baby in a cosmic cradle.
The Drake Formula was developed by Frank Drake in 1961 as a way to focus on the factors which determine how many intelligent, communicating civilizations there might be in our galaxy. The formula itself and the best estimates given by Carl Sagan, a SETI pioneer, are given in the appended texts. It is amazing to think that under this estimate our galaxy alone has about ten million advanced technical civilizations! The fundamental question facing humanity is therefore not whether anybody is out there but how to locate them and communicate with them. The ‘search’ aspect of SETI naturally takes precedence over CETI (Communication, and later perhaps contact, with Extra Terrestrial Intelligence).
In the Drake Equation, N* represents the number of stars in the Milky Way for which a reasonable estimate is 400 billion.
fp is the fraction of stars that have planets around them. Thanks to great advances in opto-electronic technology in recent years, quite a number of (large) planets have been discovered. A spate of new discoveries, including earth-like planets, is on the cards in the coming years. Planetary systems appear to be much more common than believed earlier.
ne is the number of planets per star that are capable of sustaining life. In our Solar System this number appears on current evidence to be just one. A more liberal value of two is used in Sagan’s estimate.
fl is the fraction of planets in ne where life evolves. There is no reliable basis for estimating this.
fi is the fraction of fl where intelligent life evolves. fc is the fraction of fi that develops into an advanced communicative civilization. It is very difficult to estimate the two separately. In Sagan’s estimate the product of the two factors is taken to be 0.01.
fL is the fraction of the planet's lifetime during which the communicating civilizations live or survive. This is the toughest of the questions involved in Drake’s equation. If we take Earth as an example, the expected lifetime of our Sun and the Earth is roughly 10 billion years. So far we've been communicating with radio waves for less than 100 years. How long will our civilization survive? Will we destroy ourselves in a short period like some futurologists predict or will we overcome our problems and survive very long? Only the future holds the answer.
The true value of the Drake formula is not so much in the answer itself as in the questions that are thrown up when attempting to come up with an answer. Obviously there is a tremendous amount of guess work involved when estimating the variables. However, as Astronomy, Biology, and other sciences and technology march on, the answers to these questions will emerge with continually greater reliability.
Scale of the SETI@home effort
The SETI@Home project that has been running for about eleven years now has had over 5 million voluntary contributors, with about a third of them involved actively for much of this period. Incidentally, I have been contributing significantly as a volunteer (see certificate appended) to this and other BOINC managed distributed computing projects and is among the top 6% of the SETI@home contributors worldwide (top 2% from India) since the year 2000. Billions of work units have been processed, analyzed and studied. Over 5 million years of actual computing time has been invested in the effort, most of it coming from the volunteers all over the world. It has already become the largest distributed computing project in history.
[Cobblestone (named after Jeff Cobb of SETI@home) is BOINC's unit of credit and is 1/200 day of CPU time on a reference computer that does 1,000 FLOPS based on the Whetstone benchmark]
Among the billions of work units processed so far only about 3000 have proved to be of potential interest. The rest of them have been found to be of terrestrial or natural origin. No ‘signature’ has yet been detected of any extra terrestrial intelligence. However, scientists recognize that a much greater effort needs to be mounted and run for several more decades before any definitive indicator can emerge.
Hunt for Exoplanets
It is just 15 years since the first extrasolar planet was discovered around an ordinary star in our galaxy. More than 450 exoplanets have been identified since then and the number has been growing rapidly. Understandably, most of the early discoveries were of giant Jupiter like planets. However, with major improvements in earth-based detection techniques and the NASA Kepler spacecraft launched last year specifically for such a purpose, multiple planet systems and even earth sized planets are being added to the exoplanet population. Preliminary findings indicate that one of them is inside the ‘goldilocks’ (potentially habitable) zone around its parent star. With earth like physical conditions, particularly a ‘tolerable’ temperature range, likely to prevail, such planets are the most likely candidates for the existence of advanced life forms. If their number grows at the expected rate, Carl Sagan’s estimate for ne in the Drake Equation, which has been considered by some as too optimistic, may not really be so.
The coming years are poised for some tremendously exciting discoveries that may strengthen our expectations of ETI elsewhere in our galaxy, though not necessarily in our near neighborhood.
The question of ETI belongs at present to the realm of speculation/belief, but based on sound scientific foundation. It is also based on the realization that the Laws of Science are truly universal, at both macroscopic and microscopic levels.
Evolution of life on Earth may be accidental (due to coincidence of a number of individually improbable events), but this ‘accident’ must have been replicated on a large number of planets in the cosmos. From a philosophical, psychological and practical point of view it would be the height of egotism and stupidity, a throwback to the pre-Copernican geocentric era, to assume that we are alone in the vast universe. As Carl Sagan has pointed out, such loneliness would be of a most profoundly disturbing character. In the deepest sense, the search for ETI would be a search for ourselves.
SETI involves finding powerful new ways to distinguish a genuine alien transmission from the vast earthly and cosmic background noise. It is like locating a needle in the cosmic haystack. Many decades of sustained and systematic efforts are called for before the search leads us anywhere. As of now, despite years of intense effort under SETI@home and other projects, we have not been able to find any definitive evidence of extra terrestrial intelligence. However, absence of evidence does not amount to evidence of absence.