Earth

Extra-Terrestrial Intelligence

In order to communicate with the other worlds, it requires that both sides should be highly evolved to an advanced technological stage. In 1961, Frank Drake (Figure 09-19a), now President of the SETI (Search for Extra-Terrestrial Intelligence) Institute, proposed a formula for estimating the existence of communicating Intelligent Life elsewhere in our galaxy. This is known as The Drake Equation, which states that N = R x Fp x Ne x Fl x Fi x Fc x L where

Figure 09-19a Frank Drake [view large image]

		the Milky Way that are currently broadcasting detectable signals. These chosen numbers are the lower limits and worse case scenarios. For example, a techno-logical civilization could last for 1000 years or more, dramatically increasing the value of N. Figure 09-19b depicts the parameters of the Drake equation in a pictorial form. The diagram in Figure 09-19c illustrates the stringent requirements in limiting the number of communicating civilization into a small fraction of the number of stars in the Milky Way.
Figure 09-19b Drake Parameters [view large image]	Figure 09-19c Drake Diagram

The Allen telescope array (Figure 09-19d) began operations in 2007 with just 42 antennas (out of the proposed 350 dishes). It fell victim to the budget cut in 2008. The project managed to limp along for a few years until 22 April 2011 when the SETI Institute and the University of California (at Berkeley) were forced to terminate funding of the $2.5 million annual operating costs. In spite of public misunderstanding about the usefulness of searching for ET, smaller and cheaper SETI searches are still running around the world. Some are seeking alien radio beacons, others are looking for the flicker of interstellar communication lasers.

Figure 09-19d Allen Telescope Array

There are projects looking at specific stars that seem likely to host Earth-like planets; others are doing a less sensitive but broader scan of the entire sky in the hope of catching signals of a type not yet conceived.

Thanks to the 2300 individual donations (including contribution from Jodie Foster of the 1997 movie Contact) for a total of $206,000 in early August 2011, the Allen Telescope Array may be able to hang on to its dear life if the USAF accepts the offer of using the facility to track space debris around the Earth. This is just one facet to reveal a once great power in decline. Other scientific projects such as the JWST (replacement for the HST) are also in danger of cancellation. The "debt ceiling" debacle threatens more cuts in funding things of science.

Figure 09-19e Small Scale SETI Projects

In the summer of 2004, a flurry of reports in the media indicate that radio signals (at 1420 megahertz = the hyperfine transition frequency of the hydrogen atom) have been detected three times from a point between the constellations Pisces and Aries. The transmission is very weak and shifting rapidly in frequency. It is pointed out that such drifting of frequency is too rapid to be produced by the rotation of planet and three occasions of detection is not statistically significant. The signals could be generated by a previously unknown astronomical phenomenon, or it could be something much more mundane, maybe an artefact of the telescope itself.

Figure 09-19f Search for ET [view large image]

Followings are some suggestions related to the puzzle of "where are they?"


1. It could be that primitive life may be common in the universe, but intelligent life is exceeding rare. We may be the very few that have advanced to a state where travelling in space is a possibility.
2. Another theory suggests that many plantets harbouring technologically advanced extraterrestrials exist, but space travel has fundamental limitations or inhereent dangers that we have not yet experienced. In this case, everybody is staying near home.
3. An alternate explanation about advanced extraterrestrials claims that they don't want to interfere with our development or they just don't have interest in us.
4. The absence of radio contact may be related to the fact that artificial signals are inherently weak. It is very difficult to detect. If we have ever received anomalous signal from outer space, we still have to uncover the nature of its origin.

There are three criteria to determine the intelligence of a signal:


• A narrow-band radio signal - One of the main criteria in SETI is to look for a narrow-band radio signal of the order of 1 hz, because nature cannot produce such kind of signal as shown in Figure 09-20. It has to come from an artificial source. An anomalous signal simliar to that in Figure 09-20 has actually been intercepted by SETI. Although this strange signal was never

			positively identified, astronomers have found many attributes characteristic of a more mundane and ultimately terrestrial origin. In this case, a leading possibility is that the signal originates from an unusual modulation between a GPS satellite and an unidentified Earth-based source. Many unusual signals from space remain unidentified. No signal has yet been strong enough or run long
Figure 09-20 ET Signal [view large image]	Figure 09-21 Zipf Plot [view large image]	Figure 09-22 Entropy Order	enough to be unambiguously identified as originating from an extraterrestrial intelligence.

• Optical SETI (OSETI) programs must detect a laser signal against the glare of ET's star. The best way for a laser to outshine a star is to do so very quickly, in a very short pulse lasting less than a billionth of a second. OSETI programs thus measure the light from a star in nanosecond intervals looking for a slight, brief excess of photons that could originate from a powerful pulsed laser.


• The Zipf Plot - Once an ET signal is detected, then the hunt for patterns will begin. The Zipf Plot counts the number of times different element of a language (such as letters, words, or characters) appearing in a text and logarithmically plots the frequency of occurrence of these elements in descending order. The resulting slope would have a gradient of "-1" (see Figure 09-21) for English, Chinese as well as most other languages and dolphin whistles. A "-1" slope is a sign of optimized communications: it is more efficient because elements that occur frequently (such as "a" and "the" in English) are coded to be shorter than those that are used less often. For an entirely random string of letters that contained no encoded information, the slope would be flat, or zero, because every letter occurs equally often. If Morse code is analysed one dot or dash at a time, the line on the Zipf plot is almost flat. At first glance, this would not seem like a promising signal. But if the dots and dashes are taken two at a time, the slope goes up. When dots and dashes are examined in groups of four, the slope approaches "-1".


• Entropy Order - This is a concept from the information theory developed by Claude Shannon to measure the complexity of a communication system. Zero-order entropy measures the diversity of the communicative repertoire - how many different types of elements (letters, words, whistles and so forth) make up the signal. In written English, for example, everything can be represented by 27 characters - 26 letters and a space. The entropy value is the logarithmic value (base 2) of the number of elements. The higher entropy levels, second order and up, relate to the notion of "conditional probabilities": the probability of predicting the next element in the series. If, for instance, you know the first and second words of a phrase, the third-order entropy tells you (in logarithmic form) the odds of guessing the third word correctly. Analyses of English and Russian suggest that these languages show evidence of 8^th or 9^th-order Shannon entropy. Figure 09-22 shows some examples, which relate more complex communications with higher entropy values and higher entropy orders.

There are ten strange signals detected from 2001 to 2014 by the Parkes radio telescope in Australia as reported in a "2015 New Scientist article". The signals are in the form of short duration radio wave lasting for a few milliseconds but with a rather large bandwidth. Components with different wavelength in these radio bursts are spatially separated as they travel through the interstellar medium. The dispersion in wavelength is found to be in an integer multiplication of 187.5 for all the ten measurements (see Figure 09-23a). This is the opposite of ET signaling criterion as shown in Figure 09-20. Nevertheless, these curious signals have generated considerable interests. The short time duration implies that the source cannot be larger then hundreds of kilometers; and the energy output could be enormous depending on the distance of the source from Earth. It could be a new kind of astronomical object, or may involve a new kind of physics, or originated from an unknown human technology. Failing with such kind of explanations, the source could ultimately be attributed to Extra-Terrestrial Intelligence.

Figure 09-23a Strange Signals [view large image]

According to the Optical Dispersion formula, these data points are the manifestions of either the spread of wavelength or variation of optical path length in integer steps.

In all the great oceans of emptiness, stars of type G are the best candidates to look for life - these are stars like the sun. They are of moderate, but comfortable brightness and remain stable for about 10 billion years - sufficient time for complex life forms to evolve. Tau Ceti is such a G-type, sunlike star, devoid of stellar companions and close enough for detailed studies. It was the first object searched for ET radio signals. Though Tau Ceti has about half the sun's luminosity, its habitable zone still comprises about one third AU - this is wide enough that a terran planet may have formed there. But we know from other stars that giant gas planets are common, and they are often very close to their parent star. So if Tau Ceti happens to have a system of planets, a gas giant may orbit within the habitable zone, leaving no space for an additional terrestrial planet. But this giant planet may have moons, possibly

Figure 09-23b Tau Ceti [view large image]

of Earth's size, where life may get a start. Climate on such a large moon of Tau Ceti's giant planet would not be substantially different from our own.

The Pioneers-10 space probe was launched on March 1972. In an attempt to contact "advanced civilizations", a plaque bearing engraving such as shown in Figure 09-24 was attached inside. The plaque depicts: an "average" man and an "average" woman standing before an outline of the spacecraft. a diagram showing the hyperfine transition of neutral hydrogen (spin flip of the electrons). a map locating the position of the Sun relative to 14 pulsars and the center of the Galaxy. some symbols representing the binary equivalent of decimal 8. all the planets in the Solar System with distance to the Sun in binary digits. The probe is now about 10 billion km from Earth and is flying toward the red star Aldebaran in the constellation Taurus. It will reach the

Figure 09-24 Pioneers-10 Plaque [view large image]

destination in 2 million years. So far no "alien" or "advanced civilization" has yet seen the plaque. The last signal was received on January 22, 2003.

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