The spin of a particle seems to detach and move without a body—a strange experimental observation that’s stirring up debate

With their recent preprint paper, Aharonov and Popescu, together with physicist Daniel Collins of the University of Bristol, have now described how a particle’s spin can move completely independently of the particle itself—without employing a weak measurement. In their new experimental setup, a particle is located in the left half of an elongated two-part cylinder that is sealed at the outer edges. Because of a highly reflective wall in the middle, the particle has a vanishingly small probability of tunneling through to the right-hand side of the cylinder. In their paper, the researchers provide a proof that even if the particle remains in the left-hand area in almost all cases, it should still be possible to measure a transfer of the particle’s spin at the right-hand outer wall.

“It’s amazing, isn’t it?” Collins says. “You think the particle has a spin and the spin should stay with the particle. But the spin crosses the box without the particle.”

This approach would address several of the critical concerns raised thus far. The physicists don’t need weak measurements. Nor do they need to group their experimental results to draw temporal conclusions.