Two balls suspended on threads swing side by side. Each moves on its own, but between them is an invisible thread — the attraction of masses. If gravity is quantum, it could bind them into a single whole: nudge one, and the other responds, even without contact.

Previously, it was believed that such a connection could only be observed by dropping particles into free fall, like in a tower where everything falls and weightlessness lasts for seconds. But engineers find this inconvenient: it's hard to keep particles in place and prevent them from hitting the walls. It turns out that a pendulum made of a carbon nanotube (a hundred thousand times thinner than a hair) behaves almost like a free one if the swing is fast. The error from being tethered grows smoothly, like the square of time, and remains tiny, less than one millionth, for short kicks.

The authors tested the calculation using pendulums made of such tubes. The phase, the wave advance that determines whether experimenters see quantum entanglement, barely degrades. The interference visibility (the sharpness of the fringes by which success is judged) remains high. This means that the Bose–Marletto–Vedral protocol for testing quantum gravity can be run not in a space laboratory but on a tabletop with suspended particles.

Thus, the pendulum, Galileo's ancient instrument, becomes a window into the quantum world. Freedom turned out to lie not in the absence of support, but in the speed of motion.