The Arecibo Message Explained: Messaging to Extraterrestrial Intelligence at Google Doodle today

There have been several proposals of communications with extra-terrestrial intelligences from the simple conversation with visitors from another planet, to the transmission of signal (optical and later radio) to them.

There may be other worlds besides our planet. Messaging to Extra-Terrestrial Intelligence (METI) is an idea of sending messages to other worlds which is older than Search for Extra-Terrestrial Intelligence (SETI). Attempts of METI have been made by mankind from the Greeks to present day.

The search for extra-terrestrial intelligence (SETI) is field of research that listen for a message transmitted by an intelligent alien civilisation. The first experiment was in 1961 using the National Radio Astronomy Observatory (NRAO) at Green Bank. It was conducted by Frank Drake. Many other experiments were performed since without any result so far. Those experiments are still being performed across the world.

There have been several proposals of communications with extra-terrestrial intelligences from the simple conversation with visitors from another planet, to the transmission of a signal (optical and later radio) to them.

Those proposals follow the knowledge and technology of the time. Before the discovery of the optical telescope, there has been lot of proposals involving the construction of huge structures to be put in the fire so the inhabitant of the Moon or Mars could see them. It was very difficult to imagine transmitting any other form of signal to other planets and being observed easily.

The same rhetoric applies to the radio waves. After the invention of radio by Marconi, proposals involving radio transmission started to appear. At some point in history, any concept using optical signals completely disappeared.

One of the earlier proposal came from Karl Friedrich Gauss. In 1820, he proposed the use of giant triangles, set in fire, in Siberia to communicate with inhabitants of the Moon. The construction would have required a 10-miles wide pine forest in the form of the Pythagorean triangle. Inside the triangle wheat was to have been sown to provide summer contrast with the dark green of the trees. In winter, the green of the trees would contrast strongly with the white of the snow, demonstrating the seasonal change.

He also suggested that large mirrors be constructed and attempts be made to communicate at a time when lunar beings would likely be observing the Earth and when twilight conditions would be such as to permit the mirrors to reflect light from the setting Sun and beam it to the Moon.

The real METI broadcasts started in 1962 with the transmission of a simple message toward Venus. It was a test of the Evpatoria Antenna in Ukraine. The message was simple, only three words (Lenin, Peace, and USSR) transmitted in morse. Then in 1974, a more elaborated message was transmitted from Arecibo toward M13 (a globular cluster at 25,000 light years). Since that time, several of messages have been transmitted using radio telescope.