The PSUSTRT subreddit was originally launched in March 2019 and has steadily amassed devoted fans from far and wide who enjoy sharing their discoveries with everyone online. It currently has nearly 21k members and is home to countless pictures of people and animals who found their lookalikes in the most unexpected places.

The forum encourages and welcomes a variety of posts, including eerily similar portraits found on signs, posters, ads, book covers, works of art, and other surprising locations. As you can see from a brief scroll through this list, the subreddit really knows no bounds. Which makes this an absolutely brilliant place to visit.

When you stumble upon photos of people noticing someone who looks startlingly like them, it seems like finding your double can be a fun surprise. But throughout history, however, it was anything but. In fact, stumbling upon your doppelganger — also written "doppelgaenger" or "doubleganger" — could only mean bad luck and was considered an evil warning by many folklore tales. The word itself comes from the German Doppelgänger, literally meaning "double goer" or "double walker".

It was considered (and still is!) to be a mysterious double of a living person, which led to a great deal of superstition developing around them. According to Stephen Wagner, a paranormal researcher with 30 years of experience, doppelgangers have traditionally been viewed as sinister or even evil entities and seeing one has also been considered an omen of misfortune.

Wagner pointed out many reports of doppelganger sightings are probably nothing more than cases of mistaken identity. However, he added that "such an explanation becomes harder to accept when they are seen by best friends, siblings, and parents who know the real person intimately. It seems hard to believe that they would be fooled by another person who simply resembles the original."

But whether people simply experience a bizarre lookalike phenomenon or encounter a creepy paranormal trying to snatch their life, the question still remains — are doppelgangers real? What are the odds of really meeting someone with the exact same features as yours?

Well, science journalist Zaria Gorvett noted in an article for BBC that everyone has a doppelganger, according to folk wisdom: "Somewhere out there there’s a perfect duplicate of you, with your mother’s eyes, your father’s nose and that annoying mole you’ve always meant to have removed," Gorvett wrote. "We live on a planet of over seven billion people, so surely someone else is bound to have been born with your face? It’s a silly question with serious implications — and the answer is more complicated than you might think."

Unfortunately, the research found that despite all the folklore and scary tales in literature and movies, it is highly unlikely you have a double who looks exactly like you. In 2015, Dr. Teghan Lucas, a forensic anthropologist at The University of New South Wales and Flinders University, Australia, together with professor Maciej Henneberg, published a study where they compared people for eight facial and eight body measurements (ear length and head circumference, for example) to see how alike they really were.

"If we are talking about measurements of the face there is a 1 in a trillion chance that 2 or more people will match one another on 8 measurements of the face," Dr. Lucas said in an interview with How Stuff Works.

But when she looked at the rest of the body, the odds became bleaker: "If we look at measurements of the body, the chance is even lower at 1 in a quintillion based on 8 measurements. This is because these measurements are larger and thus have a larger range which means there is less chance for people to match each other."

So according to these findings, it’s highly unlikely that someone bears a striking resemblance to another person in the true meaning of the word doppelgangers — no matter how many times your mom or best friend swears they saw someone just like you walking down the street the other day. "Two people may look very similar to the naked eye but when you start measuring they will not match each other," Dr. Lucas added.

But as it turns out, there’s still a possibility of stumbling upon someone alike. "A lot of the people we see as doppelgangers are people we don't know very well," Dr. Michael Sheehan, a neurobiologist at Cornell University, explained. "You're a lot more likely to see a doppelganger of an acquaintance than your mom. You know your mom really well. If someone looks similar you can appreciate it," he said and added that you still should be able to quickly spot the differences, in comparison to someone you don't know as well.

"There is only so much genetic diversity to go around," Dr. Sheehan told Live Science. "If you shuffle that deck of cards so many times, at some point, you get the same hand dealt to you twice."

However, that "deck of cards" is incredibly voluminous because there’s a huge number of genes that determine the facial structure, hair, eye and skin color. And they are all highly variable. And even if you’re one of the lucky ones who manage to run into someone who looks eerily similar, there’s a high chance that time and other factors like changing hairstyles will distort your doppelganger promise.

"Growing up one of my younger brothers was like the spitting image of me when I was 3," Dr. Sheehan said and added that time has also done a number on that. "We look similar-ish now, but not the same."