Alien Civilizations Sending Messages to Earth Will Die Out Before the Signal Reaches Us, Say Astronomers

Is there anybody out there? No one knows. And according to a new study, if we ever do receive a signal that intelligent alien life existed somewhere across the galaxy, those aliens would probably be long dead by the time their message reached us.

That assessment is the conclusion of an unpublished study posted on arXiv. The study expands on the current mathematical model used to consider the search for extraterrestrial intelligence, or SETI. That model, known as the Drake equation, was created by astronomer and astrophysicist Frank Drake in 1961 to estimate the number of planets in the galaxy that might harbor extraterrestrial intelligence.

"A lot of literature has been devoted to estimating the different probability factors appearing in the Drake equation to guess the number of currently broadcasting civilizations in the Galaxy," Claudio Grimaldi, a scientist at the École Polytechnique Fédérale de Lausanne and lead author on the paper told Newsweek in an email.

Our Milky Way galaxy, with the clusters of stars that scientists studied above and below its disk. T.Mueller/NASA/JPL-Caltech

The new study considered several factors contributing to the likelihood of receiving a message and the age of any civilization that would be sending it. Like ours, that distant civilization could use radio signals to transmit messages. These signals travel quickly, at 300,000 kilometers, or roughly 186,000 miles, per second.

But these signals must cover a lot of ground—or space, rather—before they could hit another habitable planet with intelligent life on it. Our galaxy alone spans 100,000 light years across. Humans have been sending radio signals for 80 years, but the first radio waves ever sent could only have traveled a maximum of 0.001 percent of the galaxy, Science News reports.

On top of that distance, however, is another consideration: civilizations don't last forever. In their new calculation, the researchers, which included Frank Drake, assumed that each civilization might last a maximum of 100,000 years. That means that if that civilization was sending radio signals for its entire lifetime, it would have reached 1,250 times as far a distance as Earth's radio waves have reached. But that's still only 1.25 percent of the galaxy.

If alien races were to send a signal, those waves would disperse and ripple through the galaxy, making spots of mixed "ghost signals." If they reached us at all, the signals would take well over 100,000 years to arrive on Earth.

That means that by the time we receive any radiation that might have come from an alien race, that race would be long dead. There's another somewhat depressing corollary here that the researchers point out: Any signals that we send into space would not reach another form of intelligent life, if it exists, until humanity was long been extinct.

This article has been updated with a quote from the lead author on the study.