In 1950, Enrico Fermi and his colleagues had a lunchtime conversation that birthed a paradox. Before arriving at the Fuller Lodge in Los Alamos, the group of scientists had been discussing recent UFO sightings, the speed of light, and a cartoon in which aliens stole New York City trash cans—a normal conversation between friends taking a break from the tough task of developing nuclear weapons. When they sat down to eat, having left the topic of extraterrestrials entirely, Fermi asked the men: “Where are they?”
Well, depending on which friend you ask, he said: “Where are they?” or “Don’t you ever wonder where everybody is?” or “But where is everybody?” They all knew what he meant. There’s a contradiction between the supposed high probability that aliens exist in abundance, and a lack of evidence pointing to an abundance of aliens. Whatever iteration, the question remains the same. If the universe is so big, and life so probable, then why haven’t our intergalactic friends come knocking?
The Search Begins
The first confirmed detection of an exoplanet wasn’t until 1992. Close to three decades on and the number of planets found orbiting around other stars has surpassed four-thousand. The Extrasolar Planets Encyclopedia, run out of the very fancy Observatoire de Paris, celebrated the milestone in March this year. The observatory’s Dr Françoise Roques told the BBC, “The great news is that we shift from a starry sky to a planetary sky…” The observatory beat NASA to the punch, which, as of writing, is sitting at 3,926 confirmed exoplanets.
Though we’ve spotted thousands of planets orbiting stars in our neighbourhood, only a small fraction may be suitable for life as we know it. We have strict guidelines for habitability. The exoplanet needs to be the right distance from the sun so liquid water can exist, it needs to have the right surface so ponds can form, it needs to be the right size, and finally, it’s home star can’t be too big. Too massive, and the star burns too quickly for life to get a leg up. Some stars only last a few million years. It took our microscopic creatures about a billion years to pop into existence.
With nothing else to go on, we’re looking for a small and rocky home as close as possible to ours.
Data from the Kepler Space Observatory suggests there could be more than two billion planets in our galaxy alone capable of harbouring life. But this is a huge extrapolation (approximately the size of two billion planets squashed together to form one gigantic ball of maybe, just maybe). But when you step away from predictions, according to Kepler archives, the number of candidate and confirmed exoplanets in a habitable zone is less than 400. These are just the planets that have found themselves in the right place at the right time. Any number of them could be entirely made up of methane or diamond or some mysterious fog that dissolves everything that ever has or ever will breathe.
Although, who’s to say these planets aren’t capable of supporting life. Life on Earth has a way of adapting to the environment in beautiful, twisted ways. Maybe what we consider a hotbed of fire is just a safe, toasty home for our extraterrestrial neighbours. As Elizabeth Tasker, associate professor at the Japan Aerospace Exploration Agency, told Space.com, “We talk about habitable planets, but the bottom line is, at the moment, we don’t know… Unless we want to risk destroying our chance to find out if the Earth is unique, we need to stop pretending we already know.”
The Drake Equation
So then, let’s use maths to try and predict what we don’t know. The only reason this barely makes sense to me is because I blindly trust anyone who can multiply numbers by other, larger numbers without sweating, so here we go. The Drake Equation aims to determine how many intelligent civilisations are in the Milky Way, or N.
N = R* × fp × ne × fl × fi × fc × L
R* is the rate of star formation
fp is the fraction of stars with planets
ne is the number of planets capable of supporting life
fl is the fraction of habitable planets where life develops
fi is the fraction of planets where intelligent life develops
fc is the fraction of life that send out detectable signals
AND
L is the length of time those creatures send signals out into space
If Frank Drake is correct, multiplying these figures should give us the number of communicating, intelligent civilisations that may exist in the Milky Way. If we are able to come up with figures for each of these values, which is a big task, the number should resemble something close to the truth. But the equation was never supposed to be all-conclusive. It was never going to be solvable. Finding out what fraction of life is sending out signals is impossible, and determining the amount of time they’ve been sending them is equally so. Drake only ever intended the equation to start a conversation about our place in the universe, and it did.
Take a Guess
The equation was written in 1961. Since then it has spat out wildly different results, ranging from the most pessimistic to the most optimistic, depending on how you feel about the presence of alien civilisations in our galaxy. The reason the result differs is that the values slotted into these parameters are shaky themselves. What is the fraction of stars with planets? We’re still counting. How many planets are capable of supporting life? Maybe 15, maybe two billion, maybe none except ours. But for decades we have been using our best estimates to come to varying conclusions.
For example, I found the results of a Drake equation discussion from 1999 in which several groups (aptly named after species from Star Trek) came up with their own results. The most optimistic was just over one thousand civilisations in this galaxy. The most pessimistic result came from the Cardassians: 0.0000000002. That’s nine zeros. As the author of this mysterious, Star Trek-fuelled discussion says, “The pessimistic numbers suggest that on average, there is no such civilisation present in the galaxy. We qualify as one, so this implies that our civilisation is a rare and transient phenomenon.”
A tweaked equation called the Statistical Drake Equation was proposed in 2010, but even the new and improved version came up with numbers between zero and 15,785. A This American Life episode on Fermi’s Paradox throws out numbers between 0.00000000009 (ten zeros) and 156 million. I tracked down a Drake Equation thread on r/askscience which proposed figures of 0.000375 and 10,000 and 4.32, and another which devolved into an argument in record time, before I got distracted by an AMA by Dr Frank Drake himself.
His username is MrDrakeEquation.
He tells the AMA that he believes we can still find solid numbers for most of the variables in the equation, but not all. “We cannot assume that our experience is similar to the experience of other civilisations. So we have to wait until we have actually found other civilisations.” What he’s saying is, we have to find alien civilisations before we can determine whether we’re alone or not. And that’s all the equation really tells us. We’re alone, or we’re not. When someone’s seven-year-old asks if Drake believes extraterrestrial life is out there he responds, “Yes I am very confident it exists and in great abundance. Right now we just have to find it. :)”
Are We Alone?
Since Enrico Fermi asked his friends one of the biggest questions we come up against, many people have tried to find a solution to the paradox. Maybe interstellar travel is too difficult. Maybe there is life, but no intelligent life. Or maybe they’re so smart, we aren’t worth the time of day. Or maybe—maybe they’re wary of approaching a civilisation which has so far been left untouched by the intergalactic opera no doubt raging around us. A sadder theory: maybe civilisations aren’t capable of sustaining themselves long enough to advance that far into the stars. And in that case, Fermi—the creator of the first nuclear reactor, the “architect of the atomic bomb”—may have answered his own question. Frank Drake suggested the price of interstellar travel might just be too high. Aliens have budgets too. There are many good and bad answers as to why our alien friends haven’t reached out. Nonetheless, it’s a question we continue to ask.
Flower & Beast 