It’s a question that has haunted and enticed humans for hundreds of thousands of years — are we alone in the universe?

We aren’t able to know for sure unless we one day meet life from another planet, but that hasn’t stopped scientists from giving their best guesses over the years.

One way of doing this is through something called the Drake Equation, invented by Frank Drake in 1961. Drake created this equation to serve as a framework for calculating the possibility of extraterrestrial life, according to a National Aeronautic and Space Administration article.

The formula is a patchwork of data-driven variables and educated guesses. It estimates how many detectable civilizations are in our very own Milky Way galaxy, represented by “N,” which simply means how many species are likely currently transmitting signals like radio out into space. So let’s take a look at the equation:

This looks like a lot, but let’s take it step by step. The first three terms, R*, f_p and n_e, represent the rate at which stars are created in the Milky Way, the fraction of stars with planets and the number of planets per system that are habitable for life, respectively.

The product of those terms gives us the amount of habitable planets in our galaxy. Research from the world’s space programs has given us relatively precise estimates for this first group, so I’ll plug in values that the University of Texas at Austin deems an average estimate.

These values would be R* = 10 stars per year, f_p = 0.5 (half) of stars have systems of planets and n_e = 0.89 planets suitable for life per solar system on average.

The fourth term, f_l, is the fraction of habitable planets on which life actually does develop. This is where the formula enters guessing territory, which makes it not very air-tight, but much more fun for people like you and me to play around with.

It’s unclear how common it is for random molecules to become basic life forms, and I would wager that it’s not too likely by random chance. So in this case I will go with a pessimistic value: 0.01, or 1 percent of hospitable planets developing life.

Next, we have f_i — the fraction of those planets with life where intelligent life emerges, which I think is very high. Intelligence has proven to be such an evolutionary advantage for humans, with our species quickly becoming dominant on our planet, so if animal-like life appears, intelligence would thrive on those planets too. But a lot of life might not make the jump from plant-types to animals, so I would place f_i at 0.6, which means 60 percent of planets that have life would produce intelligent life.

The following term, f_c, is the chance that those intelligent life forms invent a way to transmit signals like radio out into space which I think is likely, for one main reason.

Humans are our only sample of intelligent life (so far), and the Smithsonian Institute reports that Homo Sapiens have been around for about 300,000 years. That’s very little time on a cosmic scale, and we’ve already developed radio transmission capabilities. This leads me to think that most intelligent life will discover some interstellar communication, so I put f_c at 0.8, or 80 percent.

Now, last but not least, we have L, which represents how many years intelligent life forms remain detectable, or continue transmitting. The species would probably keep transmitting signals until they go extinct, leading this term to have some of the widest possible variation in the equation, but we can still speculate.

Again, our own species is the only point of reference we have. A Public Broadcasting Service article explains that radio became widespread around the early 1920s, so humans have been ‘detectable’ for almost 100 years now, but when will we stop transmitting? We’ve been around for a while, so I think the human race certainly has at least 400 years to go. This makes a total of 500 years of detectability to other life forms.

When we plug those values in we get… 10 • 0.5 • 0.89 • 0.01 • 0.6 • 0.8 • 500 = 11 intelligent, communicable civilizations in the Milky Way!

While I used a few optimistic numbers and a few pessimistic ones, this was overall a pretty rosy projection. Do you think humans are unique in the universe? Or do you think we’re just one of hundreds of civilizations? Plug in your own numbers and find out!