Drake Equation in the Search for Intelligent Life in the Universe

In the search for intelligent life in the universe, scientists have attempted to calculate the number of potential civilizations in our own Milky Way Galaxy that are capable of sending some sort of signal that we, on Earth, may be able to detect. In 1961, Dr. Frank Drake (currently on the board of Search for Extraterrestrial Intelligence, SETI) created a simple equation to calculate this number. The Drake Equation is usually written:
N = R* • fp • ne • fl • fi • fc • L
Where,
N = The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.
R* =The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = The lifetimes of civilizations capable of communication.
This equation does not have a unique solution, because several of the variables are not exactly known.  Astronomers are able to estimate several of these variable fairly accurately, but about half of these variables must be estimated with little more than an educated guess to get a reasonable solution.
By substituting reasonable estimates for all the above variables Frank Drake solved this equation and came up with 10,000 possible intelligent civilizations in the our own Milky Way Galaxy, that are capable of communications with other worlds out of a possible 100,000 billion possible planets.

So why has there not been verification of any communication with these 10,000 possible civilizations?
It is possible that time is a bigger factor than anticipated. The length of time (window) that our civilization is capable of inter-stellar communication is extremely small. While our civilization capable of inter-stellar communication (radio waves) is only a few decades old, the age of the entire universe is almost 13 billion years old. It is quite possible that there were numerous civilizations that have lived and have been destroyed before our world even existed.
So what are the odds that there are any technological civilizations actively sending out signals and listening for signals during the same period of time? It is unclear if this is taken into account in the above equation (perhaps it is included in the last variable).  The longer the lifetime of civilizations, the greater are the chances that civilizations will overlap enough for communication to take place.

Our civilization is extremely young and yet we have developed the technology to destroy ourselves several times over. Perhaps other civilizations have lived and died after developing this same technology. Perhaps there are civilizations in existence today that have not destroyed themselves. These are the ones we are looking for and hopefully our civilization will last long enough to discover them.
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Maddalena Environmental Inc.
Al Maddalena