Even after thousands of years of human experience with knots, new research from Johns Hopkins University reveals that most people cannot distinguish between strong and weak knots simply by looking at them – a finding that exposes an unexpected blind spot in our physical intuition.
Published in Open Mind | Estimated reading time: 4 minutes
From shoelaces to power cords, knots are woven into the fabric of our daily lives. Yet when researchers asked people to identify the stronger of two knots, participants consistently failed – even when given rotating views and structural diagrams. This discovery challenges our understanding of how humans perceive and reason about physical objects.
The study originated from an unexpected source: PhD student Sholei Croom’s experience with embroidery. While working on a project, Croom noticed an inability to decipher the complex tangle of threads on the reverse side – despite having created it. This observation led to a formal investigation of how people perceive knot strength.
“People make predictions all the time about how the physics of the world will play out but something about knots didn’t feel intuitive to me,” Croom said. “You don’t need to touch a stack of books to judge its stability. You don’t have to feel a bowling ball to guess how many pins it will knock over. But knots seem to strain our judgement mechanisms in interesting ways.”
The research team, including co-author Chaz Firestone, conducted a straightforward experiment: participants were shown pairs of knots with significantly different strength levels and asked to identify the stronger one. The knots ranged from the reef knot, one of the strongest basic knots known, to the aptly named grief knot, which can unravel with minimal disturbance.
The results were striking. Not only did participants consistently fail to identify the stronger knots, but even when they made correct choices, their reasoning was based on irrelevant visual features rather than the knots’ actual structural properties. Additional aids like rotating views and diagrams failed to improve performance.
The findings suggest that humans may have particular difficulty reasoning about non-rigid objects like string, even with extensive practical experience. The research team speculates that specialists like sailors or survivalists might perform better, though this remains to be tested.
Glossary
- Reef Knot: A fundamental knot known for its exceptional strength and stability, commonly used in sailing and outdoor activities.
- Grief Knot: An unstable knot that appears similar to stronger variants but can easily come undone under tension.
- Intuitive Physics: Our natural ability to understand and predict physical interactions in the environment without formal training.
Test Your Knowledge
What everyday activity did the researchers use as an example of our regular interaction with knots?
Tying shoelaces was mentioned as one of our common interactions with knots, along with neckties and power cords.
What additional visual aid did researchers provide that still didn’t help participants judge knot strength?
Researchers showed videos of the knots rotating slowly, but this didn’t improve participants’ ability to judge knot strength.
How did the researchers discover this blind spot in human perception?
The discovery originated from PhD student Sholei Croom’s experience with embroidery, when they couldn’t interpret their own embroidery knots from the reverse side.
What specific aspect of physical objects makes knot strength particularly difficult to judge?
The non-rigid nature of string makes it harder for people to reason about compared to solid objects, according to the researchers.
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