(N=R* × f p × n e × f l × f i × f c × L).
This was his attempt to estimate the number of other intelligent life forms in the Universe.
His original reason for creating this equation was not only to figure out how many other planets have life, but, also to promote Scientific discussion about extraterrestrial life in the Cosmos.
N= The number of intelligent life forms in the Milky Way Galaxy with advanced technology, who would be able to communicate with us.
(For example, they would have a radio telescope which can send and receive messages to and from other planets far away.)
R= The rate at which new stars form in our Galaxy.
Fp= The fraction of stars with planets.
Ne= Number of planets in each solar system with an environment that could support life.
Fe= Fraction of planets that could support life on which life actually appears.
Fi= The fraction of life-bearing planets that actually have intelligent life.
Fc= The fraction of civilizations that release detectable signs of their existence into space.
L= Length of time such civilizations have been releasing detectable signals into space.
This equation is only a "guesstimate" (Combination of a guess and an estimate) of how many planets in ONLY THE MILKY WAY GALAXY would possibly have intelligent life with whom we could possibly communicate.
The Milky Way is the name of the galaxy in which we live.
Each Scientist that has used this equation has used different numbers. It is just each person's individual guesstimate of how many planets in our galaxy might have intelligent life.
By using different numbers, each Scientist has come up with different answers. Some Scientists have estimated: 1,000 planets. But the most common answers have been around 2 or 3. With Earth being one of them.
Anyway, you take the number that you come up with for the amount of planets in the Milky Way and guess that more than likely, most other galaxies that support life will have approximately the same number of planets with intelligent life.
There are over 1 Trillion galaxies that Scientists have observed in the Universe. However, that to is a guesstimate. Because nobody can count to 1 Trillion.
I would guess that about half of all galaxies don't have any life at all. That leaves 500 Billion galaxies that might have life. Of those, only half of them will have a planet or Two with intelligent life. Leaving us with 250 Billion galaxies. Then, only half of those will be sending detectable signals into space. That is 125 Billion.
Galaxies only contain a small amount of everything that is in the Universe, around One percent (1%)! Everything else is just in open space. This fact was not taken into consideration in the equation. So, there could be Octillions of more planets in open space that are not in a galaxy.
With my figures, each galaxy with intelligent life would have Two planets with life forms who are trying to communicate with us or aliens on other planets. My guess would be about:
125 Billion galaxies times Two planets in each with intelligent life, which equals
250 Billion. Plus all the planets with intelligent life in open space:
1,000,000,000,000,000,000,000,000,000,(Octillion) more planets!
However, we will never know for certain how many other alien life forms are out there.
Radio signals travel at the speed of light: 186,282 Miles per Second. 5.878 Trillion Miles/year.
The nearest star is "Proxima Centauri" is about 4.2 light years away. It is part of the Alpha Centauri star system.
Most other stars are hundreds, thousands or even Millions or Billions of light years away.
Scientists on Earth have been sending signals to other stars and other galaxies for about 60 years as of this writing (August, 2019). That means our signals have only traveled a maximum of 60 light years. They have gone way past Alpha Centauri. But, all radio signals from Earth will take over 2,537,497 Million years to get to our nearest, large galaxy, the Andromeda Galaxy!
More than likely, no intelligent, alien life forms will ever receive our radio signals in your lifetime.
If a signal from Earth takes 1,000 years to get to a planet and someone can interpret it, figure out where it came from and send a signal back in the exact same direction that it came from, their signal will take 1,000 years to get back to Earth.
They can only receive, read the signal and send a signal back IF they have a Radio Telescope or something similar.
