The Actual Algebra of Finding Your Soul Mate
Breaking down the mathematical odds of winning at SoulMateRoulette.
By Maria Popova
It’s been argued that the secret of lasting love is giving up the myth of “the one” — and yet the notion of a perfect soul mate is irresistibly alluring to most of us. We go after it with remarkable ambition and even try to calculate the odds of finding that special someone, that invaluable human mirror who will “tear apart your ego a little bit, show you your obstacles and addictions, break your heart open so new light can get in.” But in a world of seven billion, how likely is it, really, that each of us will find that mythic other?
That’s precisely what NASA-roboticist-turned-comic-creator Randall Munroe explores in a chapter of What If?: Serious Scientific Answers to Absurd Hypothetical Questions (public library | IndieBound), the altogether fantastic book based on his ever-delightful and inexhaustibly original blog xkcd.
Munroe answers a reader’s seemingly simple, strangely unsettling question: “What if everyone actually had only one soul mate, a random person somewhere in the world?” Acknowledging that this proposition is problematic — “a nightmare,” he approaches the premise that each of us has “one randomly-assigned perfect soul mate” with a scientist’s vital balance of skepticism and openness, and a side of a cartoonist’s snark:
We’ll assume your soul mate is set at birth. You know nothing about who or where they are, but — as in the romantic cliché — you’ll recognize each other the moment your eyes meet.
Right away, this raises a few questions. For starters, is your soul mate even still alive? A hundred billion or so humans have ever lived, but only seven billion are alive now (which gives the human condition a 93% mortality rate). If we’re all paired up at random, 90% of our soul mates are long dead.
If this weren’t disheartening enough, Munroe assures us that things get worse when we account for the arrow of time:
A simple argument shows we can’t just limit ourselves to past humans; we have to include an unknown number of future humans as well. See, if it’s possible for your soul mate to be in the distant past, then it also has to be possible for soul mates to be in the distant future. After all, your soul mate’s soul mate is.
To make matters somewhat less messy, Munroe assumes that your soul mate is your contemporary and, with an unnecessarily judgmental remark how this would “keep things from getting creepy,” that your age difference is only a few years. With these parameters, each of us is left with a pool of about half a billion potential matches. Even so, the math remains murky — Munroe explains:
What about gender and sexual orientation? And culture? And language? We could keep using demographics to try to break things down further, but we’d be drifting away from the idea of a random soul mate. In our scenario, you don’t know anything about who your soul mate will be until you look into their eyes. Everybody has only one orientation — toward their soul mate.
Returning to the mythic requirement of identification via eye contact, he delineates the infinitesimal odds of finding your soul mate:
The number of strangers we make eye contact with each day is hard to estimate. It can vary from almost none (shut-ins or people in small towns) to many thousands (a police officer in Times Square). Let’s suppose you lock eyes with an average of a few dozen new strangers each day. (I’m pretty introverted, so for me that’s definitely a generous estimate.) If 10 percent of them are close to your age, that’s around 50,000 people in a lifetime. Given that you have 500,000,000 potential soul mates, it means you’ll only find true love in one lifetime out of 10,000.
Here, Munroe veers into a science-fictional scenario reminiscent of Malcolm Cowley’s 1930 prediction for the future of love, envisioning an artificial platform for maximizing eye contact exposure — a webcam-based system akin to ChatRoulette, which he dubs “SoulMateRoulette”:
If everyone used the system for eight hours a day, seven days a week, and if it takes you a couple seconds to decide if someone’s your soul mate, this system could — in theory — match everyone up with their soul mates in a few decades.
In the real world, many people have trouble finding any time at all for romance — few could devote two decades to it. So maybe only rich kids would be able to afford to sit around on SoulMateRoulette. Unfortunately for the proverbial 1%, most of their soul mates are to be found in the other 99%. If only 1% of people use the service, then 1% of that 1% would find their match through this system — one in ten thousand.
After further exploring this scenario to its most outrageous extremes, Munroe arrives at a strikingly familiar outcome:
Given all the stress and pressure, some people would fake it. They’d want to join the club, so they’d get together with another lonely person and stage a fake soul mate encounter. They’d marry, hide their relationship problems, and struggle to present a happy face to their friends and family.
His conclusion, however, contrasts the hopelessness of the soul mate theory with the hopefulness that keeps our hearts alive with a sense of possibility, that immutable optimism that helps us go on living and loving:
A world of random soul mates would be a lonely one. Let’s hope that’s not what we live in.
Perhaps John Steinbeck put it best: “If it is right, it happens… Nothing good gets away.
In the remainder of What If?, Munroe brings his signature blend of science, snark, and sensitivity to such mysteries as how lightning picks its targets, whether vigorously stirring a cup of tea can bring it to a boil, and what it would actually be like to travel in a time machine. Complement it with scientists’ answers to little kids’ questions about life and an illustrated tour of today’s greatest scientific mysteries.
UPDATE: For an even more comprehensive look, see English mathematician Hannah Fry’s The Mathematics of Love.
Published September 2, 2014