We have always been fascinated by the idea of alien life in the universe. It was the basis of a huge number of fantastic stories, which were limited only by our imagination. But can there be other civilizations in the vast expanses of space or on other planets and their companions?
Where are all the aliens?
The sun is just one star among the billions of stars in our galaxy. Over the past few years, scientists have discovered thousands of planets around other stars, and we know that most stars have planetary systems. So it is likely that there will be many inhabited planets in the Milky Way galaxy and beyond that galaxy that can sustain a reasonable life. Some of these intelligent civilizations, if there are any, may even have developed interstellar journeys.
Are there other intelligent life forms or are we more likely to find something primitive?
The obvious probability of life outside the solar system, combined with the lack of evidence of the existence of aliens, is called the Fermi paradox. This paradox is named after the physicist Enrico Fermi (the creator of the first nuclear reactor, considered to be one of the fathers of the "atomic bomb"), who first laid out this argument in 1950. This begs the question: where are they all? After all, with the data that we have (and they do not), the chance that the first alien civilization we have encountered will be smarter than we are is 50 percent.
As early as 1961, astronomer Frank Donald Drake tried to rationalize this question by developing an equation that takes into account all the factors relevant to the search for alien civilizations and gives the estimated number of civilizations in the galaxy that have the ability to communicate with us. Drake's equation takes into account such factors as the rate of formation of new stars, how many planets around these new and existing stars are able to support life, the number of possible planets already supporting a reasonable life. And also how many of these civilizations can have technologies that we can detect, and whether they have the ability to come into contact with us and so on.
Some numbers in Drake's equation are guesswork rather than solid facts, so the answer we get is at best an assumption. But it is worth recognizing that this equation is a good tool for attracting interest and igniting discussion on the topic of extraterrestrial life.
Searching for extraterrestrial intelligence
Scientists and radio astronomers around the world are looking for extraterrestrial intelligence on a systematic basis, one of the most famous is the SETI Project, where several international organizations, including the SETI Institute and the SETI League, are using radio telescopes to detect signals that may have been generated by intelligent life.
At one time, interest in the search for aliens was fuelled by the radio signal "Wow", which was the most "sensational" radio signal received from space and registered with the SETI project. It was recorded by Dr. Jerry Eyman on August 15, 1977, on the radio telescope "Big Ear".
In 1995, SETI launched the Project Phoenix, which used three of the world's most powerful radio telescopes: the Green Bank radio telescope in West Virginia, USA; the Aresibo Observatory telescope in Puerto Rico; and the Parkes radio telescope in New South Wales, Australia. Initially, Project Phoenix used the Parkes telescope to search for signals from 202 Sun-like stars at 155 light-years away. By the end of its work, Project Phoenix had scanned a total of 800 nearest (up to 240 light-years) stars for signs of life. The project detected some space noises, but none of them could be attributed to aliens.
Since 1999, anyone can participate in the search for extraterrestrial civilizations using their personal computers. SETI@home is a project implemented through the University of California at Berkeley (link). It uses volunteer computers to analyze radio telescope data and radio signals received by the SETI project.
There is currently excitement about sending human crews to Mars, while missions beyond the red planet are virtually impossible at this stage: the distance and travel time are too long. In fact, all research to detect life outside the Earth must be done using robotic space probes and landing rovers. These tools can provide a wealth of information and are able to explore objects to the boundary of the solar system, and possibly even beyond.
As far as life outside the solar system is concerned, the nearest stars are several light-years away, and even messages transmitted by electromagnetic waves (which propagate at the speed of light) will essentially be a one-way signal. The same applies to stars hundreds of light-years away from us, except that.