Who is Jineon Baek? The 31-year-old who solved the 60-year moving sofa puzzle without computers

Imagine wrestling a bulky sofa around a right-angled hallway bend, yelling "pivot!" like in that famous ‘Friends’ episode.

This reference clearly helps us relate to sofa shifting problems, where shifting a massive sofa through turns in the house is a big problem, leaving people dragging, tilting, and scratching their heads only to move a ‘sofa’!

But a mathematician seems to have finally given an answer to all the problems!

It all began in the 60s

In 1966, Austrian-Canadian mathematician Leo Moser posed the moving sofa problem: finding the largest rigid 2D shape that could slide and rotate around a sharp 90-degree corner in a 1-meter-wide L-shaped hallway.

Next, John Hammersley's 1968 design came up with an area of roughly 2.2074 square meters, but Joseph Gerver's more complex 1992 shape reached about 2.2195 square meters and stood as the leading candidate for decades.

Computers helped refine ideas over the years, but a definitive answer remained out of reach until Jineon Baek took it on.

Who is Jineon Baek?

Jineon Baek, 31, is a mathematics graduate from POSTECH who has gained global recognition for solving the ‘Moving Sofa Problem’, a geometry puzzle unsolved for nearly 60 years.

He first encountered the puzzle during his military service at South Korea's National Institute for Mathematical Sciences, then spent seven years building a rigorous proof during his PhD at the University of Michigan and his time at the Korea Institute for Advanced Study.

Baek's detailed 119-page paper, posted on arXiv in late 2024, proves Gerver's sofa is optimal; no larger shape can make the turn. He ditched computers entirely and used pure mathematics to reframe the puzzle as "find the absolute biggest possible shape." His proof shows Gerver's wonky sofa design squeezes every bit of space, and nothing larger can make the turn.

Baek did it out of pure human logic

What caught his eye wasn't just how tough it was, but the lack of a solid theoretical base to tackle it.

Instead of turning to computer experiments like others had, he took another approach. Over the next seven years, through his PhD at the University of Michigan and later at the June E. Huh Center for Mathematical Challenges at the Korea Institute for Advanced Study, he put together an airtight proof, one step at a time.

He produced his 119-page proof, uploaded to arXiv at the end of 2024. In it, Baek proves Gerver’s shape truly is the maximum; no bigger rigid form can squeeze around the L-shaped corner.

What is Gerver’s sofa?

Gerver's sofa is a complex, curved 2D shape proposed by mathematician Joseph Gerver in 1992 for the moving sofa problem. With an area of about 2.2195 square units, it's made of three straight lines and 15 precisely calculated arcs, like a wonky old phone handset. For decades, it was the largest known rigid form that could slide and rotate around a unit-wide L-shaped hallway corner, though unproven as maximal until recently.