Why We Rely on Judging the Strength of Knots

Despite how often we deal with knots—in shoelaces, in our wired ears, in wrapping gifts during the holidays—they can give us more trouble than we think.

Two researchers from Johns Hopkins University have shown that people always have a surprisingly difficult time wrapping their minds in knots. Their findings, detailed in a September 23 study published in the journal Open Mindthey suggest that knots may represent a new “blind spot” in our physical thinking.

The inspiration for the research came from embroidery. One day, Sholei Croom, a PhD student in the lab of Chaz Firestone—the two of whom co-authored the study—was investigating her embroidery behind a design and couldn’t make sense of how to handle the tangle of embroidery floss, even though it was her work. Instead of reacting the way most of us would (by giving up or reaching for a pair of scissors), he suspected that knots could reveal a strange gap in exact physics: what we expect from the world around us just by looking at things.

“People make predictions all the time about how the physics of the world will work but something about knots just didn’t sit well with me,” Croom said in a university statement. “You don’t need to touch a bunch of books to judge their stability. You don’t have to feel the bowling ball to guess how many pins will roll. But knots seem to strain our judgments in interesting ways. “

Croom and Firestone’s research conducted was simple. It involved four identical knots of varying strength, from the strongest (the reef knot) to the weakest (the grief knot). The researchers asked the participants to look at one pair of knots at a time, and guess which one was the strongest.

The participants failed spectacularly. They were then given videos of each knot rotating slowly, and they failed this time, too. A third iteration of the experiment presented participants with diagrams of knot formation next to each knot—but that didn’t seem to help, either. The few times participants guessed correctly, they did so for the wrong reasons. The researchers concluded that most people cannot tell the difference between a weak and a strong knot by sight.

“People are really bad about this,” Firestone said. “Mankind has been using knots for thousands of years. They’re not that complicated—they’re just strings attached. Yet you can show people real pictures of knots and ask them any decision about how the knot will behave and they have no idea.”

However, the participants were not experts, and Croom speculated that people with more knowledge of knots—such as sailors or mountain climbers—might perform better. However, he suggested that it might be harder for people to understand soft things like string or rope compared to hard ones.

“We can’t get a basic sense of the internal structure of a knot just by looking at it,” added Croom. “It’s a good example of how many open questions remain in our ability to think about space.”

So the next time you have to show a child how to tie their shoes for the umpteenth time, remember to have a little compassion—chances are you don’t know your way around knots much better than they do.