“Thanks to NASA's Kepler satellite and other searches, we now know that roughly one-fifth of stars have planets in “habitable zones,” where temperatures could support life as we know it. So one of the three big uncertainties has now been constrained.”
Adam Frank, professor of physics and astronomy at the University of Rochester
https://science.nasa.gov/universe/exoplanets/are-we-alone-in-the-universe-revisiting-the-drake-equation/
According to the Wikipedia entry for the Drake Equation, the following values were those used in the original formulation of the Drake Equation (which are also shown above in their corresponding text boxes).
R = 10 • fp = 0.5 • ne = 2.0 • fl = 1.0 • fi = 0.01 • fc = 0.01 • L = 10000
From Wikipedia:
The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
The equation was formulated in 1961 by Frank Drake, not for purposes of quantifying the number of civilizations, but as a way to stimulate scientific dialogue at the first scientific meeting on the search for extraterrestrial intelligence (SETI).[ The equation summarizes the main concepts which scientists must contemplate when considering the question of other radio-communicative life. It is more properly thought of as an approximation than as a serious attempt to determine a precise number.
Criticism related to the Drake equation focuses not on the equation itself, but on the fact that the estimated values for several of its factors are highly conjectural, the combined multiplicative effect being that the uncertainty associated with any derived value is so large that the equation cannot be used to draw firm conclusions.
Note: Some 50 years of SETI have failed to find anything, even though radio telescopes, receiver techniques, and computational abilities have improved significantly since the early 1960s.
Personally, I’m convinced there’s intelligent life out there, but the universe is so unimaginably large that any signals simply haven’t had time to reach us. Their signals are still on the way.
