In many other places of the Cosmos there must be life. It is a matter of mathematical probability. It is difficult to think that we are alone or that we are the first. For the first time in history, the human being has the necessary technology to seek life beyond Earth. But, in the vastness of the Cosmos, finding life is like looking for a needle in a haystack.
The main tool for the search for extraterrestrial life is radio astronomy. The powerful radio telescopes track the space in search of electromagnetic and radio signals, which do not have their explanation in natural astrophysical phenomena. They receive a lot of signals every day, but have not yet found anything out of the ordinary.
Radio astronomy is also the means of sending messages to space. In 1974, a message was sent from the Arecibo Observatory in Puerto Rico to the globular cluster M13, 25,000 light years away from Earth. Even if we got an answer, it would take more than 50,000 years to arrive. In 1999, another message was sent from Ukraine, the Encounter 2001 ("Encounter 2001", referring to the 2001 film Space Odyssey). This time, to a nearby area of the galaxy, rich in stars similar to our Sun.
The SETI project is, since the 70s, the program for the search for extraterrestrial life. It corresponds to the English acronym Search for Extraterrestrial Intelligence. NASA sponsored the project since its inception. But, after more than twenty years without results, at the beginning of the 90s it interrupted the financing.
The SETI did not give up and looked for new formulas to continue its work. One is the SETI @ Home. It is a computer program that anyone can download from home. Through it, SETI uses the power of personal computers of 5 million users, to process the received signals. Since 1993, SETI depends on private and amateur sponsors.
In some areas of the Solar System, simple forms of life are sought, with a biochemistry similar to ours. Apart from Mars, some moons like Europe or Enceladus are the main candidates. Outside our Solar System, the search focuses on exoplanets, planets with Earth-like conditions.
At the moment, there is only silence, and many scientists begin to be skeptical. Others are even more pessimistic. Stephen Hawking believes that, before sending information about us and our planet into space, we should know who we sent it to. Inside the galactic disk the stars are much more abundant and older than ours. If there is life, it will take us a lot of advantage. What will be their intentions towards us if they find us? Better ask ourselves, what would we do if we discovered a life much less evolved than ours?
Hawking believes that, if he ever finds extraterrestrial life, he is more likely to resemble Alien than ET. Many others share the same opinion. Arthur Clarke said: "There are only two possibilities, whether we are alone or not. And I don't know which of the two is more frightening."
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