RECENTLY, mysterious signals from outer space called fast radio bursts (FRBs) made the news. FRBs probably have nothing to do with aliens. In fact, scientists have this rule of thumb when it comes to detecting strange signals from outer space: “It’s never aliens.”
That is not a statement of conviction. Rather, it is a statement of caution and methodology. It is a reminder to exhaust all possible alternative explanation first before concluding that something unlikely is going on, something as unlikely as detecting signals from aliens.
How unlikely is detecting signals from extraterrestrials anyway? Although we might not know the answer to that question, we now have the tool to approach the question in a scientific manner. It’s called the Drake equation, named after scientist Frank Drake, who formulated it in 1961.
When scientists say, “It’s never aliens,” that does not mean they think there are no aliens out there. In fact, if you press any respectable scientist what they think, almost all of them will guess that there probably are aliens out there. The universe is simply so vast and full of possibility for life to arise elsewhere. In our Solar System alone, we are contemplating the possibility of life on Mars; Jupiter’s moons Europa and Ganymede; and Saturn’s moons Enceladus and Titan.
Now if there’s intelligent life out there, what are the chances that we will detect signals coming from them?
That’s where the Drake equation comes in. According to the equation, the number of alien civilizations in our galaxy capable of communicating to us via radio signals is equal to a product of several terms.
The first term is the average number of stars formed per year in our galaxy. That is, how many stars get born per year. We know the answer to this: It’s around 20. If we want to be a little conservative and only consider stars like the Sun—other stars might be too hot or too cold—there are two born per year.
The second term is the fraction of those stars that have planets. When this equation was first formulated, we do not know of any planet outside our Solar System. Now we know thousands. We now think that almost all stars have at least one planet going around them. One estimate is that close to 20 percent of Sun-like stars has a planet about the size of Earth.
The third term is the average number of planets that can support life. We don’t know the answer to this yet. In fact, this problem is a field of intense research.
There are several ways scientists go about attacking this problem. One is to search for Earth-like planets inside the so-called “Goldilocks zone.” This is the region not too close nor too far from the parent star, where it is neither too hot nor too cold. Another way is to try to determine what makes a planet habitable in the first place. Can life exist on Mars? How about in the ice-covered seas of Jupiter’s moon Europa or the methane lakes of Saturn’s moon Titan?
The succeeding terms are even more problematic.
The fourth term is the fraction of habitable planets—say Earth-like planets in the Goldilocks zone—that actually develop life. The thing is, we don’t even know how likely life on Earth is. Are we a very, very lucky fluke, a one-in-a-billion occurrence? In a vast universe, very unlikely things happen all the time. Or are we inevitable? Does life always arise wherever and whenever it can? In other words, is this fraction very close to 0 (life is highly improbable) or very close to 1 (life is almost inevitable), or anywhere in between?
The fifth term is the fraction of planets with life that develop intelligent life. One very big problem with this term is that we haven’t even fully understood our own intelligence, let alone that of hypothetical extraterrestrials.
The sixth term is the fraction of intelligent life that develop civilizations, that in turn develop the technology to communicate via radio signals (the best way to do it).
The last term is the punch line—the length of time such civilizations release radio signals. In our case, we have been sending intentional radio signals into outer space only since 1974.
How long do advanced civilizations usually last? How long will we last?
“Are we alone in the universe?” That is an extremely deep, extremely interesting question. But by asking this out-of-this-world question, we are forced to look at ourselves to ask questions fundamental to our origins, our place in the universe, and our destiny as a species.
That is why searching for extraterrestrial intelligence is one of the most important scientific endeavors. And although it is never aliens, one day, it might finally be.
Pecier Decierdo is resident physicist and astronomer of The Mind Museum.