The Drake Equation
This is a simple equation created
by astronomer Frank Drake
in 1961. It can be used to guesstimate the number of advanced
civilisations in our galaxy which are sending out radio
N = R* × fp × ne × fl ×
fi × fc × L
N = The number of advanced civilizations in the Milky Way Galaxy.
R* = The rate of
formation of suitable stars
The rate of formation of stars
with a large enough "habitable zone" and long enough lifetime to be suitable for
the development of intelligent life.
Estimates from Hubble Space Telescope observations: 20 per year
fp = The fraction of
those stars with planets
The fraction of Sun-like stars with planets
is currently unknown, but evidence indicates that planetary systems may be
common for stars like the Sun. Visit the Extrasolar Planets
Estimated to be half of all star systems (0.5)
ne = The number of
"earths" per planetary system
All stars have a habitable zone where a planet
would be at the right temperature to allow liquid water to flow, essential for life as we
Assume this to be 1
fl = The fraction of
those planets where life develops
Although a planet orbits
in the habitable zone of a suitable star, other factors are
necessary for life to arise.
Let's assume this to be 0.5
The fraction of
life sites where intelligence develops
on Earth took billions of years to develop. On other life-bearing
planets this may take a different amount of time, if at all.
This is more likely to occurr, given enough time. Let's assume 0.75
fc = The fraction of
planets where technology develops
The fraction of
planets with intelligent life that develop the ability to
broadcast information about their existence deep into space.
We can assume at least 0.5
The "Lifetime" of communicating
The length of time such civilizations release
detectable signals into space.
Hmmmmm, let's say 2000 years.
Using the above values, we arrive at a figure of 3,750
advanced civilisations in our Galaxy!
It is statistically incredible that humanity is alone in the universe.