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The terms of the Drake Equation are defined as follow:

• N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable (which means that communication might be possible via radio signals).
• R_* = The rate of formation of stars suitable for the development of intelligent life (number per year).
• f_p = The fraction of those stars with planetary systems.
• n_e = The number of planets, per solar system, with an environment suitable for life.
• f_l = The fraction of suitable planets on which life actually appears.
• f_i = The fraction of life bearing planets on which intelligent life emerges.
• f_c = The fraction of civilizations that develop a technology that produces detectable signs of their existence.
• L = The average length of time such civilizations produce such signs in years.

The result means the number of civilizations in our galaxy with which communication might be possible, Source: Fandom.com Drake Equation

Perhaps the most important term in the Drake equation is L, the lifetime of a civilization. How long do civilizations capable of communication last? To estimate how many civilizations there are in the Galaxy at any given time, we must know how long they last. Once lit, how long does the candle of civilization (on average) burn? Consider our own civilization, one with a recorded history of no more than 5,500 years and that has been highly technological for less than a century. Planets and stars have long life spans, but we have only a little.

So what is the average life span of a civilization? A thousand, five thousand, ten thousand, a million years? Even if, over time, there have been many, many civilizations in our Galaxy, how many are there now? Traveling to the location of another civilization in the Galaxy is a highly impractical proposition. In the best-case scenario, civilizations in the Galaxy are hundreds of lightyears apart, and getting even to the nearest star would take us (using current technology) tens of thousands of years. The civilization might be long gone by the time we got there.

The Drake equation is a mathematical formula for the probability of finding life or advanced civilizations in the universe. Source: the University of Rochester and Nasa Exoplanet Exploration

As you can see on the image above, Adam Frank and Woodruff Sullivan offered a new equation to address a slightly different question: What is the number of advanced civilizations likely to have developed over the history of the observable universe? This equation draws on Drake’s but eliminates the need for L which, as we discussed above is very difficult to determinate.

Their argument hinges upon the recent discovery of how many planets exist and how many of those lie in what scientists call the ‘habitable zone’ – planets in which liquid water, and therefore life, could exist. This allows Frank and Sullivan to define a number they call Nast. Nast is the product of N*, the total number of stars; fp, the fraction of those stars that form planets; and np, the average number of those planets in the habitable zones of their stars.

They then set out what they call the ‘Archaeological-form’ of the Drake equation, which defines A as the ‘number of technological species that have ever formed over the history of the observable Universe.’ Their equation, A=Nast*fbt, describes A as the product of Nast – the number of habitable planets in a given volume of the Universe – multiplied by fbt – the likelihood of a technological species arising on one of these planets. The volume considered could be, for example, the entire Universe, or just our Galaxy.

So are aliens real? Are UFOs real or are we alone in the universe?

If civilizations last for many millions of years, then our own Galaxy could be teeming not only with life but also with civilizations. If L is rather small (hundreds or thousands of years), then the Galaxy may be a lonely place indeed. Civilizations, like candles, may be lit frequently, but if they do not burn for very long, only a few others will be burning with us. Back to the main questions, it’s very hard to be answered exactly but if we are using a Drake Formula with optimistic numbers we can believe that we are not alone.

As a closing thought, we’d quote from the film Contact (1997), which is a must-see for everyone who is interested in Extraterrestrial Life: “There are four hundred billion stars out there, just in our galaxy alone. If only one out of a million of those had planets, and just of out of a million of those had life, and just one out of a million of those had intelligent life; there would be literally millions of civilizations out there.” – Eleanor Arroway (Jodie Foster)