Saturday, May 22, 2021
“One in 10 billion trillion is incredibly small. this implies that other intelligent, technology producing species very likely have evolved before us.”
According to Wikipedia, Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. On November 1, 1961, a number of prominent scientists held a meetup in Green Bank, West Virginia, for a three-day conference. A year before, this place had been the site of the first modern Search for Extraterrestrial Intelligence(SETI) experiment, where famed astronomers Frank Drake and Carl Sagan used the Green Bank telescope to monitor two nearby sun-like stars—Epsilon Eridani and Tau Ceti.
Frank Drake was motivated by this meetup, so were the other scientists, and he (Drake) came up with a heuristic equation to look up for possible extraterrestrial radio signals.
N = R* • fp • ne • fl • fi • fc • L
N is the number of civilizations in our galaxy we could communicate with
R* is the average rate of star formation in our galaxy
fp is the fraction of stars with planetary system
ne is the number of planets that can support life
fl is the number of those planets that will develop life
fi is the number of those planets that will develop intelligent life
fc is the number of civilizations that might develop transmission technologies
L is the amount of time that these civilizations would have to transmit their signals into space.
The purpose of the equation was to give a probabilistic argument in order to frame the discussion on SETI, rather than quantifying the number of intelligent species in our galaxy.
“As I planned the meeting, I realised a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it's going to be to detect extraterrestrial life. And looking at them, it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms."
~ Frank Drake
Although the Drake equation has achieved notable fame and great glory around the world, it has found several criticism as well. A number of variables in the equation are uncertain, and multiplying uncertain variables only increases uncertainty.
"The Drake equation was an extraordinarily useful heuristic at the outset of the modern search for extraterrestrial intelligence in the early 1960s, It guided our first-draft thoughts on the subject. Sixty years on, however, it is a creaky and aging edifice that should be swept away in favor of fresh new thinking."
~ John Gertz
John Gertz analysed all the variables of the Drake equation to determine if they were still useful for placing our bets on the possibility of intelligent life.
The parameter R* is a completely useless parameter since the rate of formation of new stars changes over time and sun like stars have a lower birth rate as compared to others. Also, there is the possibility that ET signals could be extragalactic in origin, and that the number of civilizations is unrelated to the birth of new stars. For these reasons, he suggests that R* should be replaced with “ns”, which denotes the number of candidate stars in the Milky Way that fall within our field of view.
The fraction of stars with planetary systems were largely unknown during the 1960’s. However, in the past two decades, the number of confirmed exoplanets has grown exponentially, thanks in large part to the Kepler Space Telescope. These discoveries suggest that planets are ubiquitous to stars, which makes the parameters largely irrelevant.
Next up is the parameter which includes planets like Earth - that is the number of planets that orbit around their parent star’s habitable zone(HZ). however multiple research have suggested that simply orbiting within a star's HZ is hardly the only consideration. There's also a planet's size, atmosphere, and the presence of water and tectonic activity. Gertz recommends that ne should be replaced by “ntb”, which denotes the total number of bodies (planets, moons, planetoids, etc.) that could support life either on their surfaces or beneath them.
The parameter fl is also hopelessly uncertain because scientists are not sure of how life began here on our planet Earth. There is also no consensus on whether or not life is ubiquitous or rare, owing to the fact that the search for extraterrestrial life is so data-poor.
fi - the fraction of planets supporting intelligent life is quite problematic. Since it depends on the evolutionary pathways and whether or not the factors leading to the emergence of homo sapiens are at all common.
Next parameter fc which considers the attempts made by other civilizations to contact us is problematic for the same nature. This number is highly uncertain since we have had no contact with any other civilization yet.
Last, but certainly not least, there's the tricky parameter of L, the amount of time a technologically dependent civilization will spend attempting to communicate with Earth. Over time, this parameter has come to be identified as the lifespan of civilizations, or how long they can be in an advanced state before succumbing to self-destruction or environmental collapse.
Ultimately, an updated version of the Drake Equation (based on Getz's analysis) would look like this:
N = ns • fp • ntb • fl • fi • fd • L
ns is the number of spots on the sky within our FOVs
fp is the fraction of stars with planets
ntb is the average number of bodies within each that could engender life
fl is the fraction of those that actually do give birth to life.
fi is the fraction of systems with life that evolves technological intelligence
fd is the fraction of technological life that is detectable by any means
L is the duration of detectability
Is it time to update the Drake equation?
See you next Saturday, until then have a great weekend! :)
Cheers!
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