How many extraterrestrial intelligent civilizations are out there and when will one of them send us a message?
The answers, according to a paper published in The Astrophysical Journal are 42,777 and sometime in the next 2,000 years. It’s a decent explanation for the Fermi Paradox, which asks why we still haven’t received any messages from other civilizations despite there being a high probability of them existing.
It estimates the number of possible CETIs—communicating extraterrestrial intelligent civilizations—within our Milky Way galaxy. It also looks at how probable it is that one of them could contact us and when.There are, of course, some huge unknowns behind these seemingly very precise estimates that if known would make a massive difference to the results:
- The probability of life appearing on rocky planets and eventually evolving into a civilization advanced enough to contact another.
- At what stage of their host star’s evolution such advanced civilizations would be born.
So the figure of 42,777—which has an error rate of a few hundred each side—is on the optimistic side. It’s based on an estimate that only 0.1% of civilizations could become advanced enough to contact another. This is where the Great Filter comes in.
It also takes into account the idea that any civilization would need to survive for about three million years, give or take, to reach that point.
Even if a message is ever sent to us from an advanced civilization elsewhere in the Milky Way the question remains as to whether humans can survive long enough to receive it. The authors suggest that we will need to wait as little as 2,000 years to receive one alien signal.
That’s the optimistic calculations. The authors’ pessimistic estimates are for just 0.001% of civilizations–about 111—to become advanced enough to contact another. The upshot of that would be that humans would need to wait for 400,000 years to receive a message.
“The minimum value (0.001%) we take may also be overestimated,” write the authors, Wenjie Song and He Gao at Beijing Normal University’s Department of Astronomy. “If so, the number of CETIs would become even lower, and the opportunities for communication between CETIs would become extremely small.”
The only message ever received on Earth that could have come from an extraterrestrial intelligence is the Wow! Signal, which was received in 1977 at the Big Ear radio telescope, Ohio. It was heard for 72 seconds—the maximum possible at the time—and was never repeated.
The source of that signal remains unknown though a recent paper found only one Sun-like star (called 2MASS 19281982- 2640123) in a sample of 66 in the region of the night sky that Wow! came from. It’s 18,000 light-years away.
In 2012 a paper estimated that the closest civilization to the solar system could be 1,933 light years away. So let’s send a reply? Sure—and why not, considering the chances of an advanced alien civilization being malicious are really low—though there is one problem. Any radio or laser transmission will travel at the speed of light, so would take 1,800 years to get there.
The authors note that astronomers did send the “Arecibo message” to the Great Hercules Globular Cluster (M13) in 1974 using the now collapse Arecibo radio telescope. However, it wasn’t much good. “If there are indeed CETIs in M13, their detection ability needs to be 21 orders of magnitude higher than ours to detect our signal,” write the authors. “Conversely, if they transmit a similar signal, we need to improve the detection ability by 21 orders of magnitude to detect it.”
Space is big—really big—and even in-galaxy messaging is completely impractical. Even if we’re not alone it’s doubtful we’ll ever find out.But that doesn’t stop us looking for Earth-like exoplanets around 2MASS 19281982- 2640123.Wishing you clear skies and wide eyes.
Here’s a good sign for alien hunters: More than 300 million worlds with similar conditions to Earth are scattered throughout the Milky Way galaxy. A new analysis concludes that roughly half of the galaxy’s sunlike stars host rocky worlds in habitable zones where liquid water could pool or flow over the planets’ surfaces.
“This is the science result we’ve all been waiting for,” says Natalie Batalha, an astronomer with the University of California, Santa Cruz, who worked on the new study.
The finding, which has been accepted for publication in the Astronomical Journal, pins down a crucial number in the Drake Equation. Devised by my father Frank Drake in 1961, the equation sets up a framework for calculating the number of detectable civilizations in the Milky Way. Now the first few variables in the formula—including the rate of sunlike star formation, the fraction of those stars with planets, and the number of habitable worlds per stellar system—are known.
The number of sunlike stars with worlds similar to Earth “could have been one in a thousand, or one in a million—nobody really knew,” says Seth Shostak, an astronomer at the Search for Extraterrestrial Intelligence (SETI) Institute who was not involved with the new study.
Astronomers estimated the number of these planets using data from NASA’s planet-hunting Kepler spacecraft. For nine years, Kepler stared at the stars and watched for the brief twinkles produced when orbiting planets blot out a portion of their star’s light. By the end of its mission in 2018, Kepler had spotted some 2,800 exoplanets—many of them nothing like the worlds orbiting our sun.
But Kepler’s primary goal was always to determine how common planets like Earth are. The calculation required help from the European Space Agency’s Gaia spacecraft, which monitors stars across the galaxy. With Gaia’s observations in hand, scientists were finally able to determine that the Milky Way is populated by hundreds of millions of Earth-size planets orbiting sunlike stars—and that the nearest one is probably within 20 light-years of the solar system…..
- As Ranks of Goldilocks Planets Grow, Astronomers Consider What’s Next”. The New York Times.
- Scientists in US are urged to seek contact with aliens”
- “How many alien civilizations are out there? A new galactic survey holds a clue”
- Ruminations on other worlds”
- Winston Churchill’s essay on alien life foundWinston Churchill Wrote of Alien Life in a Lost Essay”.
- Other Worlds, Other Universes
- Stephen Hawking’s universe: the cosmos explained
- Chemical Evolution and the Origin of Life
- Much-Discussed Views That Go Way Back – Avi Loeb Ponders the Early Universe, Nature and Life”
- Panspermia: A Promising Field of Research
- The privileged planet: how our place in the cosmos is designed for discovery.
- Life’s Building Blocks May Have Formed in Dust Around Young Sun”.
- New Estimate for Alien Earths: 2 Billion in Our Galaxy Alone
- Ten potentially habitable exoplanets now”
- Far-Off Planets Like the Earth Dot the Galaxy”
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