Throughout the years, the alien has been one of the most popular topics in science fiction movies and books. In fact, a lot of people are getting interested and would like to know if there is really another kind of living creature out there in space. What do they look like? Where are they coming from? Will they come and attack Earth? All these questions are the most frequently asked by the general public. The main question that interests astronomers is whether there is anyone out there in space. Scientists are trying to search for life that may exist elsewhere in the universe by using instruments and different ways to communicate with extraterrestrial life. As no evidence has proven that there is or there isnt, this seems to be a very open question.Some astronomers worked on the above question by attempting to estimate the number of advance technical civilizations in the Milky Way galaxy. They require assigning numerical values to quantities such as the number and age of stars; the abundance of planetary systems and the likelihood of the origin of life within them; the probability of the evolution of intelligent life and the lifetime of technical civilization. Results indicated that there were around a million technical civilizations in our Galaxy alone. This may seem to be such a large number. But there may be as many as 250 billion stars in the Milky Way Galaxy. Even with a million civilizations, less than one star in 250,000 would have a planet inhabited by an advanced civilization. Since we have little idea which stars are likely candidates, we will have to examine a huge number of them. (Sagan, 1979)If there are a million technical civilizations in the Milky Way Galaxy, the average separation between civilizations will be about 300 light years. (Sagan, 1979) If this assumption is correct, the time to communicate back and forward between two civilizations would be 600 years. As we can see it takes a very long tim...
