If there is anything that has caught the imagination of scientists, astronomers and ordinary people alike,  it is the possibility of existence of extraterrestrial intelligence(ETI). Human race is fascinated by the idea that we are not alone in this universe. Scientists believe that if we are there, someone else should also be there. JB. Burnell, who discovered first radio pulsars, recently said , 'we are going to get signs of life elsewhere, maybe even intelligent life, within the next century'. 
  Search for Extraterrestrial Intelligence (SETI) is the collective name for the activities people undertake to search for intelligent extraterrestrial life. Let us discuss why we should believe that there is extraterrestrial life and what are the evidences that point the finger towards possibility of ETI.

     It will be apt to start the discussion with Wow Signal! It is the best potential evidence of communication from extraterrestrials. The story goes back to 15th August 1977, USA. A researcher Dr Jerry Ehman spotted a signal at Big Ear Observatory at Ohio. As he spotted and circled the pattern on the paper log, he wrote on the paper, 'wow'. Since then,  it is known as Wow signal. Signal came from direction of constellation Sagittarius, lasted 72 seconds at frequency of about 1420.456 MHz and looked like it could be a message. This was in accordance with the theory proposed by P. Morrison and G. Cocconi in 1960s that ETI might try to contact others using radio signals (as it travel long distances and require little energy to generate) and they would pick a message that other intelligent species might understand so they might send a message mimicking hydrogen because it is the most abundant element in universe and emits a frequency of 1420 MHz. Scientists are yet to prove that it was a message from universe.

    Pulsars when first detected in 1967 by J.B. Burnell,  were thought to be a signal from ETI. They were dubbed as Little Green Men(LGM) in reference to extra terrestrial life. Scientific community has now accepted the 'lighthouse model' that pulsar is a superdense highly magnetized rotating neutrons that emit a beam of electromagnetic radiation which are visible only when the beam of emission is pointing towards earth (like a lighthouse). Some astronomers still believe that some pulsars are ETI beacons through which ETI is trying to communicate with us. 

Drake Equation was given by Frank Drake in 1961 to estimate number of extraterrestrial civilizations in Milky Way galaxy. This equation is closely related to Fermi Paradox (contradiction between estimates of high probability of existence of extraterrestrials and lack of evidence for such civilization) and Great Filter (some process must be acting as a filter to reduce the extraterrestrial civilizations). Drake suggested that large number of extraterrestrial civilizations would form but they tend to disappear quickly. Drake's equation has been criticized on the basis that several terms in the equation are based on conjecture and it cannot be used to draw firm conclusions. 

A hypothesis known as Zoo hypothesis suggest that ETI exists and they are aware of us but they do not try to contact Earth to allow for its normal development and evolution.

Another theory is based on hallucinogenic fungi. Hallucinogenic mushrooms are dispersed as spores and are capable of travelling great distances. Fungi form Fifth Kingdom of life. They are neither plant, animal, protozoa or microbes. Consumption of hallucinogenic fungi produces a different kind of perceptual state in human brain. Psychedelic professor Terence Mckenna suggested that these hallucinatory states might be a form of extraterrestrial contact. He suggested that such spores could have been seeded to Earth in remote past by alien intelligences to alter human brain perception so that it may receive messages transmitted to us. So, according to him, psychedelic experiences are a form of coded alien message though we have to decode it to understand. He also speculated that human owe their unique cognitive abilities to psilocybin (a mushroom derived substance with neurochemical effects). It is also suggested that fungi itself is intelligent and therefore ETI is living right amongst us!

About 50 tons of red particles showered (blood coloured rain) in Kerala, India in 2001. G. Louis, a physicist at Mahatma Gandhi University suggested that mysterious showers contain spores from outer space. He isolated a strange thick walled cell like structure. Many later experiments suggested a strange finding that particles lack DNA still it reproduces, even in water heated to 600 degrees.

ALH 84001 meteorite
   ALH 84001 is a meteorite found in Antarctica by US scientists in 1984. It is one of the four meteorites that are thought to be from Mars. According to a theory it was broken from Mars due to impacts of meteorites on surface of Mars 4 billion years ago and was thrown out of Martian surface by another meteorite impact 15 million years ago and it reached Earth 13,000 years ago. Analysis of the meteorite revealed remains of bacteria like life forms. This announcement caused controversy, several tests were performed on meteorite and amino acids and PAH (polycyclic aromatic hydrocarbons) were found. The debate whether the remains of life forms had their origin on Mars or were due to contamination with Antarctic ice is still going on.

Another rather interesting evidence of ETI are the UFO (Unidentified Flying Objects) sightings. Many incidences of UFO sightings has been noted. We will discuss some interesting and important evidences of UFO sights. 

In 1896-97, an unidentified mysterious light moving at thirty miles per hour was seen by hundreds of people in California. By the end of the year, hundreds of reports of its movement came from all across the Pacific coast. Though it is dismissed by skeptics as media driven mass hysteria but it is hard to dismiss thousands of reports of sightings as merely a media driven event.
 In 1947, Matt Brazell, a farmer of New Mexico City, USA discovered a debris field with scattered metallic strips near his farm. Military authorities wondered if it is due to crashed flying saucer shaped disks (UFO). However they ended the story claiming that it was due to crashed weather balloons. However in late seventies, an army officer who was sent to pick up the stuff claimed that it was extraterrestrial and sparked a controversy that is yet to die.

    Out of many alien abduction cases, Travis Walton abduction case is worth a mention. On November 5 1975 in Arizona, USA, Walton was clearing trees on a government contract along with six other members of the crew. As they began their way back home after the day, they saw a luminous flattened disc like object. As Walton went close to the object to get a closer look, a blue beam from the object hit him. Other six man ran away from the object in their truck but when they came to search for Walton a little later, he was gone! Walton returned after 5 days of his disappearance. Though initially he could not recall anything about what happened during those  5 days. Later he recalled  few things like he was in a table in a strange room, there were three horrible looking creatures looking at him and that he was subjected to various medical procedures during his stay in UFO. Various theories has been proposed to explain Walton abduction but none is satisfactory. 

On 19th September 1976 in Tehran (Iran), a UFO was spotted in the sky and many jet fighter were sent after it was picked by several radar stations. When jet fighters drew too close to the craft, it rendered all their electronic equipment inoperable and weapon system of a jet failed completely and caught fire. 

             We can see that there are a lot of evidences and theories that suggest that ETI exists. Our own existence is the biggest evidence for the existence of extraterrestrial life because given the mind boggling vastness of universe, it is highly unlikely that Earth is the only planet that sustains life. Then there is Multiple Universe theory (though not proven) that suggest that there are multiple universes which are connected by black holes. Some suggest that these multiple universes may be similar which means that we may have an Earth in each of those universes! 
Some scientists are exploring the idea of sending signals into the space for they believe ETI might catch the signal and we might get a reply. Other scientists suggest that sending a signal to extraterrestrials is not such a good idea for they may be hostile to us and may also possess a much superior technology. 

 Recently NASA's Kepler telescope identified a planet named Kepler 22b which is in the habitable zone of a Sun like star in the constellation Cygnus. It is 600 light years away from Earth. 
  There is no reason to believe that  there can be no other life form in the universe just because we don't have a concrete evidence. Carl Sagan once stated, 'absence of evidence is not evidence of absence'. Though presently we are not sure about their existence, we are likely to know about it in future, sooner or later!  



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