If an extraterrestrial civilization civilization lasted less than 100,000 years — the time it takes light to cross the galaxy — then the odds of the signals reaching Earth while the civilization is still broadcasting are vanishingly small. Humans, for example, have been transmitting radio waves for only about 80 years, so our radio waves cover less than 0.001 percent of the Milky Way.
“The signals will be from the civilization as it was,” said Frank Drake, creator of the famous Drake Equation. “It is not a remote possibility — it is a high probability — that signals we receive will be from a “civilization that no longer exists.”
If signals from an alien civilization ever reach Earth, odds are the aliens will already be dead. In an effort to update the 1961 Drake Equation, which estimates the number of detectable, intelligent civilizations in the Milky Way, physicist Claudio Grimaldi and colleagues calculated the area of the galaxy that should be filled with alien signals at a given point in time.
“If the civilization emitted from the other side of the galaxy, when the signal arrives here, the civilization will already be gone,” says physicist Claudio Grimaldi, of the Federal Polytechnical School of Lausanne in Switzerland.
The team, reported Science News and Mercury News, which includeed Frank Drake (now a professor emeritus at the SETI Institute in Mountain View, Calif., and the University of California, Santa Cruz), assumed technologically savvy civilizations are born and die at a constant rate. When a civilization dies out and stops broadcasting, the ghostly signals it had sent continue traveling like concentric ripples on a pond.
Electromagnetic signals (blue circles) from alien civilizations shown in the image above will continue traveling through the Milky Way even after the aliens are gone. The appearance of a doughnut hole represents when a civilization dies out.
Scientists gathered at the SETI Institute in Mountain View, California this past March to chart new approaches to answering the question: are we alone? The conference, titled “Decoding Alien Intelligence”, sought to broaden perspectives and expand the methodologies applied in the effort to detect extraterrestrial technology:
“New tools are available that can enable this approach and help us decipher the evolutionary and probabilistic nature of advanced alien life,” said organizer and SETI Institute Director Nathalie Cabrol. “We can build a new roadmap that is multidisciplinary, that opens the toolbox.”
A recently released update to the Drake Equation – a framework for discussing the probability of intelligent life existing beyond Earth – is receiving a fair bit of media buzz. The Drake equation was developed during the outset of the modern SETI field to act as a framework for the scientific community to discuss the probability of advanced extraterrestrial life. The probabilistic argument was devised by pioneer in the search for extraterrestrial intelligence, Dr. Frank Drake, who participated in the new study.
According to the study, if advanced aliens exist on the furthest edge of the galaxy from us, any signals traveling at the speed of light will not reach us for quite some time. Any signals that do reach our planet will likely be vestiges of a long dead civilization.
“The signals will be from the civilization as it was,” said Drake. “It is not a remote possibility — it is a high probability — that signals we receive will be from a civilization that no longer exists.”
There’s the chance that it’s still alive “but no longer be transmitting,” Drake said. “Or it may have changed in a very big way, such as migrating from the planet to escape its expanding star.”
Senior astronomer at the SETI Institute, Seth Shostak, still sees the value in collecting such a message: “To me, it is like finding a bottle on a beach with a note in it,” said Shostak. “It may be that whoever put the note in is long gone. But at least you know there’s somebody on the other side of the world.”
It’s important to remember that determining the longevity of a potential alien race based on the still-developing example of our own survival has a limited value, as SETI Institute’s Andrew Fraknoi points out:
“Until we know more about our longevity, it is pure guesswork,” he said. “Every year we don’t destroy ourselves, we add one more year to what we know civilizations can do.”
Surprisingly, the team also calculated that the average number of E.T. signals crossing Earth at a given time should equal the number of civilizations currently transmitting — even if the civilizations we hear from aren’t the same ones presently broadcasting. Grimaldi is now working on a paper about what it means that we’ve found none so far.
Image below: A case study of the inhabitants of Easter Island served in part as the basis for a mathematical model showing the ways a technologically advanced population and its planet might develop or collapse together. Rochester astrophysicist Adam Frank and his collaborators created their model to illustrate how civilization-planet systems co-evolve. (University of Rochester illustration / Michael Osadciw)
The Daily Galaxy via SETI Institute and Science News
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