Scientists have been long fascinated by the idea of another intelligent civilization emerging from another planet in the cosmos. In hopes to estimate the number of stars that can have intelligent species capable of communicating with us, radio astronomer Frank Drake devised an equation in 1961 that can estimate the odds of us making contact with extraterrestrial life by calculating the product of increasingly restrictive series of fractional values.

According to Search for Extraterrestrial Intelligence, the Drake Equation is usually written as:

N = R* • fp • ne • fl • fi • fc • L

In which,

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 length of time such civilizations release detectable signals into space.

In a recent study, researchers from the University of Rochester and University of Washington tinker with the equation a bit to negate three uncertainties that can be found in the equation.

The first uncertainty, the number of planets per solar system that are in "habitable zones" are constrained thanks to NASA's Kepler satellite and other planetary satellites that discovered roughly one-fifth of stars have planets suitable for life.

For the second uncertainty, how long civilizations might survive, researchers expanded the question "how many civilizations may exist now?" to "Are we the only technological species that has ever arisen?" By doing so, the researchers eliminated the uncertainty regarding the longevity of civilizations, but instead shifted the focus to how often does life evolve to an advanced state in the history of the universe.

The researchers then constrained the third uncertainty, calculating the probability for advanced life to evolve on habitable planets by again flipping the question. They calculated the odds against intelligent life occurring, instead of guessing the probability of advanced life developing, in order for humanity to be the only advanced civilization in the entire history of the observable universe.

By using this approach, researchers can calculate how unlikely advanced life must be if there has never been another example among the universe's ten billion trillion stars, or even among our own Milky Way galaxy's hundred billion.