A certain kind of obsession only affects those who are already aware of the complexity of seemingly simple things. That type of person is retired Boston University astrophysicist Kenneth Brecher. Like all children at Hanukkah, he spent his childhood spinning dreidels at his neighborhood synagogue, tossing them on tables, and gambling chocolate coins. The spinning top was merely a game for the majority of his life. Nothing more. “I would say I had never mentally connected dreidels with physics — I swear to God,” he once confessed.
When Brecher was researching neutron stars, the incredibly dense remnants of supernovae that rotate hundreds of times per second, that began to change sometime in the late 20th century. He needed a method for his undergraduate students to understand precession, which is the wobble in the axis of a spinning object. Thus, he began constructing model tops. It was intended to be a teaching aid. A brief comparison. It changed completely.
Brecher found that spinning toys are surprisingly difficult to model, as does anyone who studies the physics of spinning tops. Friction, mass distribution, density, and shape all affect spin, and even slight modifications to any one of those factors have unpredictable effects on the dynamics. Two German physicists set out to write a concise summary of top physics in the late 1800s. After fourteen years, they had produced four volumes with a combined page count of one thousand. Even so, they were limited to describing what Brecher refers to as “trivial tops.”
As it happens, the dreidel is not a very good top. In contrast to what you want for stability, its four-sided body tightly packs mass around the central spin axis. Similar to a paper plate stuck halfway down a pencil, a good top distributes weight outward. Conventional dreidels are made to fall. That is the entire purpose of the game. But Brecher wasn’t going to stop there.
He experimented with dozens of 3D-printed versions over the years, changing proportion and shape until he discovered designs that performed odd, amazing feats. Like a hard-boiled egg on a kitchen counter, his PhiTOP has precisely the right geometry to rise from horizontal to vertical while spinning. Presented at the 2021 Bridges Conference, his DeltaCELT is purposefully asymmetrical; if you spin it clockwise, it will automatically stop, rattle, and reverse direction. It has an almost living quality.
It’s difficult to ignore the project’s poetic undertones. In retirement, a man who studied the spin of collapsed stars—objects so dense that a teaspoon weighs a billion tons—perfects the spin of wooden and plastic toys. The same rules apply to physics. Whether you are a four-sided top on a synagogue table or a neutron star, angular momentum is unaffected.
NASA participated as well. Four hundred kilometers above Earth, in December 2023, astronaut Jasmin Moghbeli of the International Space Station spun a dreidel. Through the porthole, the top continued to drift and spin against the backdrop of our planet without being pulled down by gravity. Similar work was done in 1993 by Jeffrey Hoffman, who observed that the dreidel’s behavior completely changed in the absence of gravitational torque. Pure, continuous spin without any nutation or precession.
Hundreds of tops and dreidels, each a tiny experiment in classical dynamics, are now part of Brecher’s collection. A hand-carved wooden globe that is unremarkable to look at but seems to be exquisite to spin is his favorite. He doesn’t refer to them as toys. He refers to them as wonders and scientific curiosities. That seems about right, considering how much trouble they’ve caused physicists over the past 150 years.