At just 31, this Korean genius cracks a math riddle unsolved for 60 years

Move over, Ross Geller. There’s a new couch hero in town, but instead of yelling “Pivot!” in a stairwell, he’s outmaneuvering one of geometry’s most stubborn riddles—with nothing but his wits and a passion for pure math.

The Mobile Sofa Problem: Not as Cozy as It Sounds

If you thought mathematics was above discussing sofas, think again. For nearly sixty years, the mobile sofa problem has had the world’s sharpest minds scratching their heads. The riddle, posed in 1966 by Austro-Canadian mathematician Leo Moser, sounds deceptively simple: imagine trying to squeeze a rigid sofa around a right-angled corridor (an L-shaped hallway) exactly one meter wide. Easy for cartoon characters, not so much for math. The challenge is to determine the largest possible shape that can slip through without the help of a sledgehammer—or an angry landlord.

This question, simple enough for a child to grasp, has lingered in math textbooks, captivating professors and students across the globe. For decades, mathematicians chipped away at possible solutions, much like sculptors patiently coaxing a statue from marble. The progress? Slow, but steady.

• In 1968, British mathematician John Hammersley suggested a sofa shape of about 2.2074 square meters.
• In 1992, Rutgers University’s Joseph Gerver significantly improved it, devising a curved figure with an area of 2.2195 square meters.
• No one has improved on Gerver’s result since. Yet, no one had managed to prove that a larger sofa was impossible—until now.

Baek Jin-eon: A New Hope for a Classic Puzzle

Enter Baek Jin-eon, a 31-year-old mathematician who cracked the mobile sofa conundrum where generations had failed. Baek first encountered the problem during his mandatory military service, working as a researcher at the National Institute for Mathematical Sciences. Something about the puzzle nagged at him. There was no clean theoretical framework—no sturdy foundation to build on. Just a seemingly silly, unsolvable question floating, conceptually weightless, in the math universe.

This lack of structure became Baek’s obsession. For seven years, he chased the answer. He worked on it through his PhD at the University of Michigan, then as a postdoctoral researcher at Yonsei University in South Korea. Driven not by computers but by the elegance of logic itself, Baek refused to take the digital shortcut many predecessors used. There would be no computer simulations, no brute-force calculations—just pure, rigorous reasoning and a mind with very little patience for unsolved mysteries.

And after years of relentless pursuit? At 29, Baek solved the riddle, proving what no one had before: Gerver’s sofa really is as big as it gets—a mathematical limit that cannot be bested. His demonstration filled 119 densely written pages. If your sofa manual looks daunting, try a math treatise at this density.

Recognition and Legacy: Not Just a Math Victory

Baek published his results on arXiv in late 2024; the paper is now being reviewed by the Annals of Mathematics, one of the field’s most prestigious journals. The feat didn’t go unnoticed: Scientific American named Baek’s work one of the ten greatest mathematical breakthroughs of 2025. With characteristic humor, they compared the achievement to the famous Friends scene in which Ross Geller yells “Pivot!”—only this time, the solution took 119 pages instead of a frenzied shout.

But what drives a person to wrestle with such a puzzle for years? Meeting Baek, you find someone who’s dreamed of mathematics since childhood. “When I learned in third or fourth grade that you could study mathematics as a profession, it became my dream,” he says. Even when his family struggled financially, Baek refused to let go. “Even if I did something else, I don’t think I could abandon the beauty of mathematics.” His research process has an almost artistic resonance: “You keep hope, then crush it, and move forward gathering ideas from the ashes,” he told the Korean Institute for Advanced Study. “By nature, I’m more of a dreamer. For me, mathematical research is a repetition of dreams and awakenings.”

Today, as an associate researcher at the June E Huh Center for Mathematical Challenges, Baek regards his success not as an end point, but as a seed. “It takes time for a problem to gain its context,” he comments, ever the philosopher among mathematicians.

What Comes After the Sofa?

With the mobile sofa now marked as “mission accomplished” in the math universe, Baek isn’t putting his feet up just yet. He’s moving on to new optimization problems and the challenges of combinatorial geometry. The world of mathematics may have one less sofa stuck in the hallway, but as Baek knows, there are a thousand more puzzles waiting in the wings.

So the next time you struggle to move furniture, take comfort in this: somewhere, a mathematician is proving not just how to pivot, but why there are limits to how massive your sofa can actually be.