Do you know: How scientists try to find alien civilization?
In the last fifty years, evidence has steadily mounted that the components and conditions we believe necessary for life are common and perhaps ubiquitous in our galaxy. Planets beyond our solar system, while once relegated to the domain of speculation, are now known to be common and numerous. Nevertheless, no evidence exists for the presence of life outside of the Earth. However, on our own planet, life is known to have arisen early and flourished. And while the propensity for the evolution of intelligence from basic forms of life is not currently well understood, it appears that intelligence has imparted a strong evolutionary advantage to our own species. The possibility that life has arisen elsewhere, and perhaps evolved intelligence, is plausible and warrants scientific inquiry.
Referring NASA’s Kepler mission there are roughly one trillion planets in our Milky Way galaxy; three times more planets than stars. Billions of these planets are Earth-sized and in the "habitable" or so-called "Goldilocks" zone - not too distant from their host star (too cold), and not too close to their star (too hot). And there are billions of other galaxies outside our Milky Way galaxy - plenty of places where life could emerge and evolve. There may even be primitive extraterrestrial life in our own solar system, perhaps on a moon of Jupiter or Saturn. Europa, one of Jupiter's moons, is thought to have a liquid water ocean beneath its icy surface, perhaps a good environment for life as we know it.
Scientists send signals between planetary systems. Sending interstellar messages are potentially much easier than interstellar travel, being possible with technologies and equipment which are currently available. However, the distances from earth to other potentially inhabited systems introduce prohibitive delays, assuming the limitations of the speed of light. Even an immediate reply to radio communications sent to stars tens of thousands of light-years away would take many human generations to arrive.
The SETI project has for the past several decades been conducting a search for signals being transmitted by extraterrestrial life located outside the Solar System, primarily in the radio frequencies of the electromagnetic spectrum. Special attention has been given to the Water Hole, the frequency of one of neutral hydrogen's absorption lines, due to the low background noise at this frequency and its symbolic association with the basis for what is likely to be the most common system of biochemistry (see Alternative biochemistry). The regular radio pulses emitted by pulsars were briefly thought to be potential intelligent signals; the first pulsar to be discovered was originally designated "LGM-1", for "Little Green Men." They were quickly determined to be of natural origin, however. Several attempts have been made to transmit signals to other stars as well. (See "Realized projects" at Active SETI.)
One of the earliest and most famous was the 1974 radio message sent from the largest radio telescope in the world, the Arecibo Observatory in Puerto Rico. An extremely simple message was aimed at a globular cluster of stars known as M13 in the Milky Way Galaxy and at a distance of 30,000 light-years from the Solar System. These efforts have been more symbolic than anything else, however. Further, a possible answer needs double the travel time, i.e. tens of years (near stars) or 60,000 years.