Search for Extraterrestrial Life: The Existence of Non-Human Intelligent Beings in Our Galaxy The possibility of extraterrestrial life has always intrigued philosophers, scientists, theologians and even lay people for centuries. The fascinating question of whether there are other intelligent creatures in space, however, remains unsolved despite technological advancements in science particularly because thus far, there still lacks conclusive evidence. Motivations for the search for non-human life range from scientific and philosophical levels, technical and practical levels, to even the need to eliminate the loneliness of the human race in time and space. Scientists and astronomers remain committed to the search because the answer to this question has profound consequences: it will explain the nature and destiny of intelligent life on the universe, the culmination of evolution in different galaxies and provide more insight on the role of human beings on the universe, as well as what they are capable of accomplishing (Drake, 1988). Lineweaver (2006) also explains that there is also the possibility that extraterrestrial life will provide the human race with important technological and scientific information that might take them numerous resources and hundreds of years to establish.

Notable scientists such as Stephen Hawkins and Carl Sagan adopt the mediocrity principle that posits that intelligence life is likely to exist in other planets because the universe is too huge to only accommodate the human race. The National Aeronautics and Space Administration, NASA (2015) also estimates that there are over 100 million worlds in the Milky Way galaxy that are bound to accommodate complex forms of alien life that are yet to be discovered. Nevertheless, some assert that the possibility that life might exist in other galaxy is not proof that it actually exists, and they conclude that the human race is the only form of intelligent life in the universe. This text seeks to explore the debate on extraterrestrial life further. It starts by reviewing findings and scientific arguments that favor the possibility of other forms of life in the Milky Way galaxy. It goes on to evaluate how life might exist in non-earthlike conditions and the differences believed to exist between simple and intelligent forms of life. It then takes a look at the counterarguments from those who assert that extraterrestrial life is unlikely based on their own scientific hypotheses, and concludes with an answer to the question about the existence of extraterrestrial life in this galaxy.

Scientific arguments favoring the existence of extraterrestrial life

Astrobiology, which is the study of extraterrestrial life, has been able to accomplish numerous milestones since the dawn of space exploration since the 1960s. In 1953, William Whemell, a British philosopher, published his book titled 'Of the Plurality of Worlds: An Essay', which raised issues similar to modern day arguments of life in other planets. He argued that there were other planets that orbited the stars (Aczel, 1998). In 1974, Carl Sagan, an American astronomer and astrobiologist, estimated that more than a million civilizations might exist in the Milky Way galaxy alone and since there are billions of galaxies in the universe, this implied that the number of intelligent alien species was enormous (Ward and Brownlee, 2003). Sagan then assembled messages that could be sent to space to test this theory, through the Voyager Golden Record and the Pioneer Plaque, which were designed such that they could be understood by extraterrestrial beings that may have found them.

Dr, Frank Drake came up with an approach that would estimate the number of civilization that might be in existence in the universe. He came up with the Drake equation, which summarized the main concepts scientists had to consider when assessing the possibility of extraterrestrial life. According to Drake (1988), the equation posits that the number of civilizations in the Milky Way galaxy with which radio communication was possible (N) was the product of; the average rate of star formation necessary for intelligent life (R*); the fraction of these stars that had planetary systems (fp), the number of planets in a particular solar system that could support life (ne); the fraction of planets on which life actually appears (fl); the fraction of planets that could support life when it appears (fi); the fraction of civilizations that were capable of developing technology that can release signs of their existence into space (fc); and the approximate length of time such civilizations could release the detectable signals into space (L). The National Research Council has often emphasized the relevance of the Drake Equation in searching for manifestations...

He then speculated that other chemical bases such as silicon could also support life using the strong anthropic principle that supposes there are many different universes, each having different values of atoms and physical constants that could support life (Hawking, n.d). Evidence that there was still life on earth billions of years ago also suggests that there is a good chance there was spontaneous generation of life in other planets. DNA might have replaced earlier forms of cell organizations such as RNA, which had the potential of reproducing themselves in other form in different locales of the universe. Although Hawking (n.d) states that there exists many other life forms in the galaxy, he asserts that the possibility of this life developing intelligence is low particularly because it took two and a half billion years for human single cells to develop to multi-cells, a necessary precursor to intelligence. Scientists have often argued that the extinction of dinosaurs was caused by a collision of the earth with a small body, more than 60 million years ago. Hawking posits that the existence of intelligence on earth can be attributed to the absence of such a collision in the last 70 million years.
Findings that support the existence of life in the Milky Way galaxy

NASA has been able to inspect planets and moons at close range to investigate the possibility of life. In 1976 NASAs Viking Landers detected chemical signatures in Mars that indicated life may exist in the planet (NASA, 2015). An experiment was conducted where radioactive carbon nutrients were mixed with soil to test for the production of radioactive methane gas. The result was positive, which implied that there was something in the soil that metabolized the nutrients in order to produce the methane gas. However, the test was later declared a false positive because other similar tests that were conducted failed to provide evidence of life. In 1977, a strange pulse of radiation was detected by the Ohio State University Telescope near the constellation Sagittarius, suspected to have been a result of an unexplained astronomical event or a message with powerful transmitters. The signal still baffles scientists and philosophers to date. In 1996, NASA (2015) claims that scientists discovered rocks in Mars that contained mineral magnetite and organic molecules found on a variety of Earth bacteria.

Numerous discoveries in the 21st century continue to fascinate philosophers, theologists and scientists. For instance, in 2001, the infrared signal given off by Europa, Jupiter's moon, was explained by frozen pieces of bacteria, which are a sign of life. In 2002, the University of Texas also established that microbes may be living in Venus, which would explain the limited presence quantities of sulphur dioxide, hydrogen sulphide and carbon monoxide (Kelly, 2012). The University posited that microbes living in the Venusian atmosphere could also explain the carbonyl sulphide they had been found. Traces of sulphur on Europa were also interpreted as a sign of waste products of bacteria colonies by Italian scientists in 2003. NASA (2015) explains that in 2004, astronomers received another suspicious signal from a section between the constellations Aries and Pisces. Although it was probably a natural phenomenon, some astronomers still insist that it was a frequency that transmitted by aliens wishing to be noticed. Of particular excitement were the discoveries of the Kepler 22b, 20f and 20e, Earth sized planets, by NASA's Kepler Space Telescope in 2011 (Kelly, 2012).

Approaches used in the search of live in the Milky Way galaxy

To understand the approaches used in the search of live in the Milky Way galaxy, it is imperative to first establish what scientists, astrobiologists and astronomers look for in their search for life in the Milky Way galaxy. Rosenthal (2011) explains that life on Earth is organic and hence needs water, oxygen and minerals for sustenance. In looking for life on other planets, therefore, scientists look for other chemical elements that sustain human life, or cell fragments that function in a way that would support other forms of life. They examine dust and particulate matter from space hoping to find biological entities made up of oxygen and carbon, the building blocks of life. Other basic elements they search for include hydrogen and nitrogen, which attach themselves to form large molecules that are the building blocks of proteins that make DNA and life. Aczel (1998) also states that scientists try to identify habitable localities in the…