Quote:The Drake equation states that:The old results are
where:
N = the number of civilizations in our galaxy with which communication might be possible;
and
R* = the average rate of star formation per year in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fℓ = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time such civilizations release detectable signals into space.[3]
Quote: * R* = 10/year (10 stars formed per year, on the average over the life of the galaxy)But the new results are:
* fp = 0.5 (half of all stars formed will have planets)
* ne = 2 (stars with planets will have 2 planets capable of developing life)
* fl = 1 (100% of these planets will develop life)
* fi = 0.01 (1% of which will be intelligent life)
* fc = 0.01 (1% of which will be able to communicate)
* L = 10,000 years (which will last 10,000 years).
Drake's values give N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000 = 10.
Quote:Current estimates (see below):So we are not alone if the illusive deities of chaos and luck are not mean to us
R* = 7/year, fp = 0.5, ne = 2, fl = 0.33, fi = 0.01, fc = 0.01, and L = 10,000 years
N = 7 × 0.5 × 2 × 0.33 × 0.01 × 0.01 × 10,000 = 2.31 (so two communicative civilizations exist in our galaxy at any given time, on average, plus two hundred more that are not trying to communicate).
But a pessimist might equally well believe that suitable planets are rare, life seldom becomes intelligent, and intelligent civilizations do not last very long:
R* = 10/year, fp = 0.5, ne = 0.01, fl = 0.13, fi = 0.001, fc = 0.01, and L = 1000 years
N = 10 × 0.5 × 0.01 × 0.13 × 0.001 × 0.01 × 1000 = 0.000065 (we are almost surely alone in our galaxy).
Alternatively, making some more optimistic assumptions, assuming that planets are common, life always arises when planets are favorable, 10% of civilizations become willing and able to communicate, and then spread through their local star systems for 100,000 years (a very short period in geologic time):
R* = 20/year, fp = 0.5, ne = 2, fl = 1, fi = 0.1, fc = 0.1, and L = 100,000 years
N = 20 × 0.5 × 2 × 1 × 0.1 × 0.1 × 100,000 = 20,000 (there's quite a few civilizations, although the closest one would still be about 1500 light years away).