Astronomers Adam Frank and Woodruff Sullivan, at the University of
Rochester and the University of Washington respectively, published a paper in the May issue of the journal Astrobiology
exploring what they call the “cosmic archaeological question”: “How
often in the history of the Universe has evolution ever led to a
technological species, whether short- or long-lived?”
Frank summed up their conclusion in an op-ed for the New York Times,
published June 10: “While we do not know if any advanced
extraterrestrial civilizations currently exist in our galaxy, we now
have enough information to conclude that they almost certainly existed
at some point in cosmic history.”
We now have enough information to conclude that they almost certainly existed at some point in cosmic history.
, University of Rochester
The astronomers came to this conclusion by reworking the famous Drake
equation from a different perspective, also adding up-to-date
information. The equation was originally formulated by astronomer Frank Drake in 1961 to calculate the odds of contact with alien life.
Drake studied radio astronomy at Harvard and held various posts in
the field, including at NASA’s Jet Propulsion Laboratory. He included in
his equation various factors, such as the rate of formation of stars
suitable for the development of intelligent life and the number of
planets in each solar system with an environment suitable for life (See
the image below if you want to see Drake’s entire equation).
Improvements in astronomical observation technology have greatly
boosted our knowledge of exoplanets. In April, the Kepler spacecraft
team announced the discovery 1,284 planets outside our solar system.
Frank wrote in his op-ed: “Three of
the seven terms in Drake’s equation are now known. We know the number of
stars born each year. We know that the percentage of stars hosting
planets is about 100. And we also know that about 20 to 25 percent of
those planets are in the right place for life to form. This puts us in a
position, for the first time, to say something definitive about
extraterrestrial civilizations.”
By looking at the probability of an alien civilization having ever
existed, instead of currently existing, Frank and Sullivan also
bypassed the time-constraints built into Drake’s factors.
“This left us with only three unknown factors, which we combined into
one ‘biotechnical’ probability: the likelihood of the creation of life,
intelligent life, and technological capacity,” Frank wrote. He
concluded: “The odds that we are not the
first technological civilization are actually high. Specifically,
unless the probability for evolving a civilization on a habitable-zone
planet is less than one in 10 billion trillion, then we are not the
first.”
In 2013, mathematicians at the University of Edinburgh made a similar statement about the probability of alien cultures having sent probes to Earth.
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