“Our galaxy may be teeming with technologically active life or populated by a single very long-lived civilization. In either case, we should be incredibly lucky to get a detection one day,” wrote physicist Claudio Grimaldi in an email to The Daily Galaxy about the possibility of there being a fundamental flaw in why we have not received a signal from an advanced alien civilization.
How would we decode such a signal? What if alien species communicate chemically? Will they use the language of math and science, or signaling at 1420 megahertz, which is naturally emitted by hydrogen, the most common element in the universe? What if a message or the technology of its signal is beyond our comprehension?. What if it’s a message from a long extinct civilization?
“Illumination” of Earth by Alien Emission
“The physical significance of the volume fraction of the galaxy occupied by hypothetical artificial EM emissions is indeed no other than the probability of our planet being “illuminated” by at least one EM emission (our planet being illuminated is the necessary prerequisite to get a detection),” continued Grimaldi in the email to The Daily Galaxy. “One interesting property is that, in average, a handful of long-lived signals could cover a fraction of the galaxy comparable to that covered by many short-lived emissions.
“Furthermore,” adds Grimaldi, “if we assume that the signals have been emitted independently of each other, the galactic volume fraction occupied by the emissions allows us to infer an upper bound on the mean number of emissions crossing Earth. It turns out that we need the galaxy being more than half-filled by artificial emissions in order to have, at any time, typically more than one signal impinging upon Earth.”
The human species has been transmitting radio waves for only about 80 years, so our radio waves cover less than 0.001 percent of the Milky Way. Electromagnetic signals (blue circles shown below) from alien civilizations 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.
Surprisingly, 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, reported The Daily Galaxy in 2018 in “First Contact” –May be Ghost Signals from Long-Vanished ET Civilizations.”
In an effort to update the 1961 Drake Equation, which estimates the number of detectable, intelligent civilizations in the Milky Way, Grimaldi and colleagues calculated the area of the galaxy that should be filled with alien signals at a given time.
“If the civilization emitted from the other side of the galaxy, when the signal arrives here, the civilization will already be gone,” says Grimaldi, with the Federal Polytechnical School of Lausanne in Switzerland.
The Dark-Forest Theory
“No civilization,” Liu Cixin, China’s foremost philosopher of first contact and author of the Three Body Problem, told The Atlantic’s Ross Anderson, “should ever announce its presence to the cosmos. Any other civilization that learns of its existence will perceive it as a threat to expand—as all civilizations do, eliminating their competitors until they encounter one with superior technology and are themselves eliminated.”
This grim cosmic outlook, Liu says, is called “dark-forest theory,” because it conceives of every civilization in the universe as a hunter hiding in a moonless woodland, listening for the first rustlings of a rival.
Liu told Ross that “he doubts the dish will find one. In a dark-forest cosmos like the one he imagines, no civilization would ever send a beacon unless it were a ‘death monument,’ a powerful broadcast announcing the sender’s impending extinction. If a civilization were about to be invaded by another, or incinerated by a gamma-ray burst, or killed off by some other natural cause, it might use the last of its energy reserves to beam out a dying cry to the most life-friendly planets in its vicinity.”
Liu told Ross that he’s hesitant to make connections between his books and the real world, but said that his work is influenced by the history of Earth’s civilizations, “especially the encounters between more technologically advanced civilizations and the original settlers of a place.”
Similar to European Invasion of the ‘Middle Kingdom’ of China?
One such encounter occurred during the 19th century, Liu observed, “when the ‘Middle Kingdom’ of China, around which all of Asia had once revolved, looked out to sea and saw the ships of Europe’s seafaring empires, whose ensuing invasion triggered a loss in status for China comparable to the fall of Rome.”
The “appearance of this Other” might be imminent, Liu warns, and that it might result in our extinction. “Perhaps in ten thousand years, the starry sky that humankind gazes upon will remain empty and silent,” he writes in the postscript to one of his books. “But perhaps tomorrow we’ll wake up and find an alien spaceship the size of the Moon parked in orbit.”
The Daily Galaxy, Avi Shporer, Research Scientist, MIT Kavli Institute for Astrophysics and Space Research via The Atlantic and Claudio Grimaldi. Avi was formerly a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL)
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