Why Scientists Started Sending Messages to Aliens Instead of Just Listening

For sixty years, scientists have listened for signs of intelligent life beyond Earth. A parallel effort goes the other way: instead of waiting for a signal, it sends one. Universe Today has begun a series on the history of that practice, known as Messaging Extraterrestrial Intelligence, or METI, and the first installment explains where the idea came from.

The short version, according to Universe Today: METI grew out of the same puzzle that drives the search for alien signals, the lack of any evidence that life exists elsewhere, and for decades the same people worked on both.

The question behind it all

Universe Today describes what it calls the “Great Silence”: humans have studied the sky for as long as they have recorded it, yet have found no sign of life beyond Earth. The outlet notes that the puzzle is often called Fermi’s Paradox, though it argues the label is a misnomer, since the idea was neither Fermi’s alone nor truly a paradox.

The argument rests on the scale of the cosmos. Universe Today cites estimates that the observable universe spans 96 billion light-years, that it holds more than 2 trillion galaxies, and that it began about 14 billion years ago with the Big Bang. Galaxies range from dwarfs with 1,000 to several billion stars up to giants with as many as 100 trillion. The chemical ingredients of life, such as carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, appear to be abundant everywhere.

How the thinking developed

• 1950: During a lunchtime conversation at Los Alamos National Laboratory about UFO sightings, physicist Enrico Fermi asked where everybody was. He and his colleagues reasoned that if interstellar travel were feasible and desirable, Earth should already have been visited several times.
• 1960: Cornell astrophysicist Frank Drake led the first search for extraterrestrial intelligence, known as Project Ozma.
• 1975 to 1982: In a series of papers, physicists Michael Hart and Frank Tipler argued that the puzzle could be resolved only if extraterrestrial life does not exist. That view became known as the Hart-Tipler Conjecture.
• 2005: The term “Active SETI” appeared to describe sending messages into space meant for extraterrestrial recipients.
• 2006: Russian scientist Alexander Zaitsev coined the term Messaging Extraterrestrial Intelligence to separate sending from searching.

Many scientists, Carl Sagan among them, pushed back on the Hart-Tipler reasoning. They argued that there are countless possible reasons humans have not yet heard from anyone, with “yet” the key word. In the phrase Sagan and William Newman made well known, absence of evidence is not evidence of absence.

Listening and sending were once one project

Universe Today says early researchers did not distinguish between the two approaches and pursued both at once. Drake, who ran Project Ozma, was also central to what the outlet calls the first true METI project, the Arecibo Message, roughly fourteen years later. Sagan, a leading figure in early SETI work, later teamed with Drake on the Arecibo Message, the Pioneer Plaques and the Voyager Golden Records.

Zaitsev’s 2006 proposal framed the divide as a Hamlet-like choice: “To send or not to send?” In his view, SETI deals with searching for messages from aliens, while METI deals with creating messages to them. He wrote that SETI scientists can address only a narrow question, whether transmitting to attract attention makes sense for the sake of finding something, while METI pursues the broader aim of overcoming the Great Silence.

Why it matters

The history shows that sending a message to space is not a fringe offshoot of the hunt for alien life. It grew from the same question and the same researchers. It also explains why the field has its own name: Zaitsev proposed one precisely because listening and transmitting raise different questions, and the debate over whether to send at all depends on that distinction.

For readers following the search for life elsewhere, the series offers context for later debates. This first part covers the early ideas and experiments, and Universe Today has said it will continue the history in further installments.

Around Prague, based on reporting by Universe Today