If a person is lost in the desert, they have two options. They can research civilization, or they can make themselves easy to spot by lighting a fire or writing HELP in big letters. For scientists interested in the question of whether intelligent extraterrestrials exist, the options are much the same.
For more than 70 years, astronomers have searched for radio or optical signals from other civilizations in search of extraterrestrial intelligence, called SETI. Most scientists are confident that life exists on many of the 300 million potentially habitable worlds in the Milky Way galaxy. Astronomers also believe there is a good chance that some life forms have evolved intelligence and technology. But no signal from another civilization has ever been detected, a mystery called “The Great Silence”.
While SETI has long been a part of mainstream science, METI, or extraterrestrial intelligence messaging, is less common.
I am an astronomy professor who has written extensively on the search for life in the universe. I also serve on the advisory board of a nonprofit research organization that designs messages to send to extraterrestrial civilizations.
In the coming months, two teams of astronomers will send messages into space in an attempt to communicate with any intelligent extraterrestrials who might be listening.
These efforts are like making a big bonfire in the woods and hoping someone finds you. But some people wonder if it is wise to do so.
The first attempts to contact life off Earth were quixotic messages in a bottle.
In 1972, NASA launched the Pioneer 10 spacecraft to Jupiter bearing a plaque with a line drawing of a man and a woman and symbols to show the origin of the craft. In 1977, NASA continued with the famous Golden Record attached to the Voyager 1 spacecraft.
These spacecraft, along with their twins, Pioneer 11 and Voyager 2, have now all left the solar system. But in the vastness of space, the chances of these or any other physical objects being found are incredibly tiny.
Electromagnetic radiation is a much more effective beacon.
Astronomers transmitted the first radio message designed for extraterrestrial ears from the Arecibo Observatory in Puerto Rico in 1974. The series of 1s and 0s were designed to convey simple information about humanity and biology and a was sent to the globular cluster M13. Since M13 is 25,000 light years away, you shouldn’t hold your breath for an answer.
In addition to these deliberate attempts to send a message to extraterrestrials, wayward signals from television and radio broadcasts have leaked into space for nearly a century. This ever-expanding terrestrial babble bubble has already reached millions of stars. But there’s a big difference between a focused burst of radio waves from a giant telescope and a diffuse leak – the weak signal from a broadcast like i love lucy fades to the buzz of radiation left behind by the Big Bang soon after it left the solar system.